CFA Piling vs. Rotary Bored Piling


CFA (Continuous Flight Auger) piles are quick to install and they offer an efficient solution for more lightly-loaded structures.

Using our CFA rigs, we can offer the best and most cost-effective solution for our clients’ projects across the UK. Our knowledge and expertise, as well as our experienced site team and on-board technology, means that we can monitor quality and performance real-time.

CFA technology offers the ideal solution for projects in urban locations because it eliminates vibration and disturbance to adjacent structures, and it reduces noise emissions.

Continuous CFA piles are suitable for most soil conditions and construction projects. They are the best and most effective solution when piling is required close to existing buildings, or in built-up areas because this piling approach is virtually vibration free, and it has low noise levels.

CFA Drilling technique: Continuous flight auger piles are constructed rotating an auger string into the ground by injecting concrete under a minimum pressure through the hollow stem of the auger. The soil is replaced with concrete in one continuous movement as the auger is withdrawn. After the pile head is cleared of debris, steel reinforcement is plunged into the pile concrete.

The technique requires no additional ground support, such as casing or drilling fluids, because the bore is self-supporting as the auger is rotated into the ground and the concrete supports the bore after extraction.

Ground conditions: CFA piling is amenable to a broad range of ground conditions from medium dense sands and gravels through to stiff clays and even low grade rock. The technique is not recommended in very soft clays or silts or in very loose sands or gravels.


Advantages of CFA Piling:

  • High production rates mean that piles are commercially attractive
  • Broad range of auger sizes (300mm to 1200mm diameter) means that the most economical use of construction materials is possible
  • Depths of up to 25m means that CFA piling is effective for low to mid-range loading thus suitable for most commercial and residential projects
  • Low noise emissions
  • Virtually vibration free

Sectors: residential, commercial (multi-storey), urban locations




Rotary Bored Piling is carried out by our Large Diameter Piling (LDP) rigs which offer higher power (torque) than our CFA rigs so they are more agile and able to overcome underground obstructions.

When constructing rotary bored piles we have the ability to quickly change coring or digging tools and auger type to best suit soil conditions. We can also install plunge columns in the pile to facilitate top-down construction. Compared with other piling techniques LDP can offer larger load capacities and be installed to far greater depths.

Drilling technique: Rotary bored piles are constructed by rotating a casing into the ground to support poor or granular ground and then removing the pile bore using an auger, bucket or coring unit attached to a telescopic Kelly bar. Once the bore is fully cleaned out to design depth, the pile concrete is tremied into the bore and the casing is extracted leaving a finished pile. Typically, pile reinforcement is cast into the pile during concreting.

Ground conditions: Rotary piling can be employed in almost all ground conditions from soft ground supported by temporary casing through to high grade very strong rock cored in to open-hole techniques.


Advantages of Rotary Bore Piling:

  • Amenable to almost all ground conditions including rock drilling
  • Depths achievable up to 60m with casing and tool diameters up to 1.8m means that very high capacity loads can be achieved
  • Minimal ground disturbance and vibration – resulting risk to adjacent structures and property is limited
  • Simple and efficient installation process
  • Ability to construct sockets into underlying rock
  • Larger diameters feasible
  • Can extend to greater depths when compared with any other piling technique

Sectors: commercial (tower), civils, marine




Types Of Concrete And Their Strengths

Finding the right type of concrete for your project is essential for getting the best results. Here at EasyMix Concrete we design and supply a huge range of concrete strengths and grades to ensure the ideal solution for any project or application.

Concrete Mixes

Most concrete mix designs use the same type of raw materials: cement, water and aggregate (usually sand and stone), in different ratios. Some types of concrete have additional materials added to give specialist qualities, such as:

  • Fibres – enhanced strength
  • Plasticisers – free flowing, better workability
  • Retarding agents – reduce rate of setting
  • Accelerating chemicals – increase rate of setting
  • Corrosion inhibitors – reduce corrosion of steel rebars 

Have a look through our glossary of concrete types to make sure you get the right concrete for your project. If you’re not sure, or would like to discuss you requirements, simply give the team at EasyMix a call. Even if we can’t supply the exact type of concrete you require, we’ll be more than happy to discuss your project, recommend alternatives and ensure you get the right materials for the best results.

Glossary of Commercial Concrete Types

C7/8 / GEN 0

C7 & 8 concrete mix, Gen 0 concrete or wet lean mix concrete, is commonly used in both commercial and domestic projects for a huge range of general applications, such as kerb bedding, haunching and backing, domestic foundations and blinding.

Ideal for: Cavity filling, kerbing, domestic foundations & haunching.

C10 / GEN 1

C10 concrete, or Gen 1 concrete is an extremely versatile mix used throughout the construction industry for general and housing applications. This includes un-reinforced strip, trench fill and and agricultural applications.

It can also be used for drainage works and blinding house floors, as well as pad foundations and non-structural mass concrete in non-aggressive ground conditions.

Ideal for: Foundations for steps, trench fill, floor blinding & drainage works.

C15 / GEN 2

C15 concrete or Gen 2 concrete is suitable for house floors with no embedded metal. It also provides the ideal material for flooring when no permanent finish or floor covering will be installed, such as carpet or tile.

Ideal for: Foundations for small walls, sheds & conservatories. Paving for steps and paths.

C20 / GEN 3

C20 concrete mix and Gen 3 concrete is commonly used for lightweight domestic applications and foundations, such as driveways and garage, shed & workshop bases. It can also be used to construct internal floor slabs so long as they contain no embedded metal.

Ideal for: Foundations for large walls, garages, houses & extensions. Paving for patios. Reinforced bases & oversites for conservatories, garages, sheds, greenhouses.

C25 / ST 2

C25 standardised mix concrete or ST2 Concrete is widely versatile and used in numerous commercial and domestic projects. It is commonly used for footings and foundations, including mass concrete fill, trench fill and reinforced fill, as well as general groundworks. It can also be used for kerbing, infilling around manholes and small bases for external furniture, such as patios.

Ideal for: Foundations and reinforced bases for houses & extensions. Trench fill, kerbing & patios.

C30 / PAV1 / ST 3

C30 concrete, PAV1 concrete and ST 3 concrete are the most common types of concrete used for pavement construction.

It is also ideal for lighter use external applications, such as slabbing, as well as outdoor paved areas such as stables, driveways, walkways, patios and garages.

PAV 1 mixes have an air entrainment additive to create standard sized air bubbles in the concrete. This helps to protect the surface from freeze-thaw cycles, making it especially useful for outdoor paving.

Ideal for: Paving external kennels and reinforced hard standings. Reinforced bases for workshops and unreinforced bases for houses & extensions.

C35 / PAV2

C35 concrete and PAV2 concrete is a heavy-duty use concrete. It offers high quality similar to PAV1, but is much more substantial making it suitable for commercial and industrial use. Common applications include raft foundations, piling and external slabbing and pacing that will be subject to the constant loading and scraping imposed by industrial vehicles and machinery.

PAV 2 mixes have an air entrainment additive to create standard sized air bubbles in the concrete. This helps to protect the surface from freeze-thaw cycles, making it especially useful for outdoor paving.

Ideal for: Reinforced bases for commercial buildings and agricultural light storage areas.


C40 concrete is a strong commercial grade concrete mix most commonly used in the construction of structural and support beams, footings and foundations, roadworks, and in agricultural use.

Ideal for: Foundations for septic tanks, paving HGV parks and agricultural yards.


hot and cold rolledCustomers often ask us about the differences between hot rolled steel and cold rolled steel. There are some fundamental differences between these two types of metal. These differences relate to the ways these metals are processed at the mill, and not the product specification or grade.

Hot Rolled

Hot rolling is a mill process which involves rolling the steel at a high temperature (typically at a temperature over 1700° F), which is above the steel’s recrystallization temperature. When steel is above the recrystallization temperature, it can be shaped and formed easily, and the steel can be made in much larger sizes. Hot rolled steel is typically cheaper than cold rolled steel due to the fact that it is often manufactured without any delays in the process, and therefore the reheating of the steel is not required (as it is with cold rolled). When the steel cools off it will shrink slightly thus giving less control on the size and shape of the finished product when compared to cold rolled.

Uses: Hot rolled products like hot rolled steel bars are used in the welding and construction trades to make railroad tracks and I-beams, for example. Hot rolled steel is used in situations where precise shapes and tolerances are not required.

Cold Rolled

Cold rolled steel is essentially hot rolled steel that has had further processing. The steel is processed further in cold reduction mills, where the material is cooled (at room temperature) followed by annealing and/or tempers rolling. This process will produce steel with closer dimensional tolerances and a wider range of surface finishes. The term Cold Rolled is mistakenly used on all products, when actually the product name refers to the rolling of flat rolled sheet and coil products.

When referring to bar products, the term used is “cold finishing”, which usually consists of cold drawing and/or turning, grinding and polishing. This process results in higher yield points and has four main advantages:

  • Cold drawing increases the yield and tensile strengths, often eliminating further costly thermal treatments.
  • Turning gets rid of surface imperfections.
  • Grinding narrows the original size tolerance range.
  • Polishing improves surface finish.

All cold products provide a superior surface finish, and are superior in tolerance, concentricity, and straightness when compared to hot rolled.

Cold finished bars are typically harder to work with than hot rolled due to the increased carbon content. However, this cannot be said about cold rolled sheet and hot rolled sheet. With these two products, the cold rolled product has low carbon content and it is typically annealed, making it softer than hot rolled sheet.

Uses: Any project where tolerances, surface condition, concentricity, and straightness are the major factors.

The difference between civil engineering and structural engineering

Civil and structural engineering are two engineering disciplines. The engineering disciplines deal with designing, evaluation, preservation and construction of elements. The difference between civil engineering and structural engineering is tricky. This is because the task of discerning the two disciplines would be difficult before understanding the concepts behind each of the careers.

Civil engineering

This is one of the oldest engineering disciplines. Its history dates back to the ancient times when people began building shelters for themselves. The engineering discipline is offered in the universities and the field of specialization includes: roads, water treatment, canals and dams.

Civil engineering is offered in the university has a four year full time course. After graduation, civil engineers join subdisciplines of civil engineering.Therefore, it is very rare to find a course referred to as masters in civil engineering. The disciplines of civil engineering includes: Geotechnical engineering, transportation engineering, structural engineering and environmental engineering.

Structural engineering

Structural engineering deals with the designing, Analysis, building and maintenance of resisting or load bearing structures. Examples of those structures are: bridges, skyscrapers and dams. This is an engineering field which is offered in the universities as a subject under civil engineering and as a specialization which results in master’s degree or PhD.

What is the difference between civil engineering and structural engineering?

Even though both engineering disciplines belong to the same field, they vary in several aspects. One of the differences is that civil engineering focuses on design elements while structural engineering is more concern on inspecting the materials used for construction. The structural engineers are the one who are supposed to ensure that the materials used for construction can support the design of the structure.

Another difference between the two engineering courses is that civil engineering is offered as the first degree while structural engineering is offered as the 2nd or 3rd degree in engineering. A civil engineer is expected to perform the duties of a structural engineer. However, the vise versa is not true. In fact, structural engineering is a subject which is under civil engineering and it is also offered as masters or doctorate degree.

In conclusion, the two degree courses are very crucial when it comes to design and construction jobs. As a result, the engineering firms provide both civil and structural engineering services to its clients. Therefore, both engineering courses are significant in any of the construction or development projects.If you need to pursue any of the careers, it is important that you understand the differences mentioned above.

Drained vs Undrained Loadings in Geotechnical Engineering

One thing that takes a while for the budding geotechs to digest is the difference between undrained and drained parameters, and when to use what. Actually, it is simple and is common sense. When a saturated clay is loaded, it will not let the water out immediately (i.e. remains undrained) and that is when most of the failures occur. In the short-term, the clay can be treated as an undrained homogeneous material where we will not separate the grains and water. Here, we carry out the undrained analysis in terms of total stresses, using undrained shear strength cu (phi = 0).

In the long term (after some months or years), the clay will drain out some water until the excess pore water pressure is fully dissipated and the pore water pressure is in equilibrium with the in situ conditions. Now, it is prudent to carry out an effective stress analysis using c’ and phi’, where we separate the stresses acting on the pore water (pore water pressure) and the grains (effective stresses).

Undrained analysis is often much easier to carry out, inexpensive to get the design parameters, and is necessary to assess the short-term stability which can be more critical than the long term stability. For undrained loading, the failure envelope in terms of total stresses is horizontal and hence we only need one parameter, undrained cohesion cu (phi = 0). Undrained cohesion can be derived from an unconfined compression test, UU triaxial, vane shear test (lab or field) or simply using a pocket penetrometer. Drained analysis needs c’ and phi’ which are derived from more expensive consolidated drained or undrained triaxial tests or in situ tests (and estimated using correlations). They are necessary when working with effective stresses. We generally charge A$1500-A$2000 for a CD or CU triaxial test on three specimens at different confining pressures, while an unconfined compression test costs less than A$100.

Granular soils drain very quickly, and hence they are always treated as drained and analysed in terms of effective stresses using phi’ (c’=0). For normally consolidated clays c’ = 0. Even for other clays (compacted or overconsolidated), c’ is not very large and is in the order of 0-25 kPa. Danish code suggests that c’ can be taken as 0.1 cu.

In summary, short-term analysis is carried out in terms of total stresses, using undrained shear strength parameters cu and phi = 0. Long-term analysis is carried out in terms of effective stresses, using drained shear strength parameters c’ and phi’.



第一部分 获取优质土地,产品定位精准






































第二部分 做好前期策划,实现快速开工








































3、提前邀请当地政府官员参与开工典礼,并沟通当地主流媒体发布,扩大品牌及项目影响力, 摘牌后即通过户外广告牌、新闻宣传进行品牌导入。


第三部分 聚焦展示区域,确保完美开盘


























































第四部分 过程管控到位,主体质量合格

















(6)推行约谈和督办制度:约谈是由集团召集相关项目和施工单位领导进行面谈,指出存在的质量问题,要求制订整改方案和计划,按期完成整改。督办是由集团工程管理中心派专人驻点项目,协助区域和项目解决对极少数施工队伍质量管理的老大难问题;对个别极端不配合的施工单位, 坚决进行清退,避免后期交楼风险。
















第五部分 重视精装策划,打造精品货量
































































第六部分 注重细节完善,实现完美交楼


















































(1)项目集中交付后1个月内,区域客户关系管理部负责收集汇总客户交付评价及居住体验评价等信息,提交产品及服务质量分析报告;(2)对整体交付区域影响客户生活、设计及施工缺陷能够得到有效评估和整改,减少客户重点问题的投诉升级,减少客户生活中的不便,改善园区服务品质,提升客户满意度。  碧桂园”拿地即开工”的背后,到底是什么东西在”作怪”?

Evolution of Building Elements

1 Foundations

Late 19th century

In 1875, the Public Health Act was introduced. It required urban authorities to make byelaws for new streets, to ensure structural stability of houses and prevent fires, and to provide for the drainage of buildings and the provision of air space around buildings. Three years later the Building Act of 1878 provided more detail with regard to house foundations and wall types. The Local Government Board, itself established in 1871, issued the first Model Bye-laws in 1877/78 (‘by’ or ‘bye’ is old Danish and means local).  With regard to foundations, the bye-laws stated that walls should have stepped footings (twice the width of the wall) and implied that concrete (9″ thick – 225mm) should be placed under the footings unless the sub-soil be gravel or rock (‘solid ground’). Text books of the time suggested that Portland cement made the best concrete although hydraulic lime was the next best thing. Common lime (hydrated lime) was seen as a much inferior product. A mix of approximately of 1:1:4 or 1:1.5:5 was recommended, cement:sand:stone. It is not clear how many local authorities adopted these bye-laws outside London; many produced their own – often less onerous than the Model ones.

The drawing below shows a section of a proposed house (Bristol 1898). You an see the main walls have brick footings with concrete below.

The London County Council was created in 1889, and sponsored the London Building Act of 1894 which amended the rules relating to foundations and the thickness of external and party walls. This seems like a backward step – they no longer mention concrete footings, instead relying just on brick ones. A writer at the time noted, “the bye-law on the whole is a wise one, as concrete is so easily scamped, but there are many cases in which concrete alone would be more economical and more stable”.

Part of the requirements for external walls and footings from The London Building Act 1984 is shown below. By today’s standards the foundations seem very shallow; in fact many text books from the time suggest that foundations should never be less than 12 inches (300mm) deep and often much more. These standards were generally higher than those adopted by provincial towns and cities.

Many local authorities were slow in adopting Model Bye-laws; even where they did, building control was fairly lax. This meant that the nature and quality of foundations varied considerably. The graphics below show typical foundations at the end of the 1800s. The depths varied according to circumstances but generally they were shallower than their modern counterparts.

The drawing below dates from 1903 and shows a section through a planned house. The foundations look quite shallow (and there are no brick footings). Whether or not this was just a drawing convention of the time we do not know; presumably the depth of the actual foundation would depend on specific circumstances.

Reinforced foundations were not unknown. G Lister Sutcliffe states, “..frequently the metal is in the form of steel rails….or twisted wires…  embedded in the concrete.  A stronger foundation can be obtained in less depth than when concrete alone is used”.

Between the Wars

During the 1920s and 30s foundations remained much the same. Text books from the 1930s suggest that in clay soils foundations should be 3 feet deep (900mm) – guidance in fact not much different from today.  London Building Acts and Model Bye-laws introduced a number of minor amendments (see below). The examples below were suitable for houses with foundations in firm clay or coarse sand.

Note that the 1939 bye-laws still permitted brick footings and also mentioned the option of rafts and piles.

The foundation below was built in the early 1930s.  It’s about 500mm wide, 200mm thick and probably 400mm, or so, deep.

Post 1945

In the late 1940s and throughout the 1950s most new houses were built with strip foundations. Raft foundations were also popular, particularly under system-built properties or over areas of fill. A typical raft comprised a concrete slab 6″ to 9″ thick (150mm to 225mm), suitably reinforced. A few foundations were piled – short bored piling systems became common during the early 1960s. The piles were typically 6′ to 12′ long (1.8 to 3.6m), not normally reinforced but with a reinforced ground beam over the top, cast on some form of compressible material (ash or clinker).

The Model Bylaws were replaced by National Building Regulations in 1965. These Regulations were applied generally throughout England and Wales, with the exception of the Inner London Boroughs (the area of the former London County Council) where the London Building Acts continued to prevail. Various amendments and revisions to these Building Regulations were issued increasing the scope and areas covered by Building Regulations. This continued until the Building Act 1984 finally consolidated Building Regulations under one piece of legislation. This resulted in the introduction of the Building Regulations 1985 that came into operation in November 1985.

The Building Regulations contain ‘deemed to satisfy’ provisions for strip foundations. For modest loads and on certain types of ground acceptable strip foundation widths are given – see the Building Regulation section for the table itself.  Outside these boundaries, for example a 4 storey building on soft clay, the foundation has to be specifically designed.

Raft foundations and piled foundations do not have any ‘deemed to satisfy provisions’ and always need to be designed.  Today, rafts are comparatively rare except in former mining areas. Piling has become very common for four main reasons; it’s much cheaper than it used to be, smaller, lighter piling rigs are now available, shoring traditional trenches is expensive, and brownfield sites are often not suitable for strip foundations.

There is much more information on piling in the Foundations section of this web site.

2 External walls

Early Brickwork

During the 1700s there were a number of improvements in brick making. Blended clays, better moulding techniques and more even firing gave greater consistency in brick shape and size. Fashion dictated brick colour: the reds and purples popular in the late 1600s gave way to softer brown colours in the 1730s. By 1800 the production of yellow London stocks provided a brick colour not that much different from natural stone. The repeal of the brick tax in 1850 gave the brick industry a new impetus. Improved mixing and moulding machines, together with better firing techniques, allowed brick production to reach new heights. Bricks were now available in a range of colours, shapes and strengths that would have been unimaginable a 100 years earlier. Better quarrying techniques allowed extraction of the deeper clays which produce very strong, dense bricks; vital for civil engineering works such as canals, viaducts sewers and bridges.

Brick bonding

By the end of the 19th century most houses had walls of at least one-brick thickness. Houses over three storeys often had thicker walls, usually reducing in thickness at each upper-floor level. The brickwork itself (at least the brickwork on view) was generally laid to a very high standard. Most houses were built in Flemish bond although rear walls or walls hidden by render were often laid in Garden wall bond (usually English).


Stone was often used for prestigious buildings or in areas where it naturally occurred. In upland areas (the north and west) stone was often the obvious choice for building because it was readily available (and prior to the railways these were often areas where bricks were expensive). There are 3 groups of stone; igneous, sedimentary and metamorphic. The sedimentary group, which includes limestone and sandstone, accounts for most of the stone used for building in the UK.

Rubble walling is found in a variety of styles. At its cheapest it comprises rough stonework, built as two outer leaves and bound together with copious amounts of lime mortar. More expensive work comprised squared rubble possibly set against a brick backing. In most situations a stone wall has to be thicker than a brick one. So, whereas a 1 brick thick wall (215mm or so) might be fine for a two or three storey house, a stone wall is likely to be 325mm or even more. Most rubble walls were pointed flush or slightly recessed. The ribbon pointing so often seen nowadays is not traditional, neither is it particularly durable.

Stonework which is dressed and/or finely cut is often referred to as dimensioned stone. Sometimes it’s referred to as freestone. This means it can be worked (cut, shaped and smoothed) with a chisel and a saw in any direction. It has a fine grain and is free from obvious laminations and pronounced bedding planes. In the 18th century whole cities were built (some rebuilt) in stone. It was not cost effective to build the whole of the wall in freestone and a backing material of rubble or brickwork can nearly always be found. In some houses only the front elevation would be built in freestone, the sides and back being constructed of rubble or brick. To bond the two halves of the wall together, ‘through’ or bonding stones were used.

Where the freestone is laid with very fine joints, almost invisible from more than few feet away, the work is knows as ashlar. In some parts of the country the stones were cut with a taper to make the joints easier to form. Wedges made from bits of timber or even oyster shells were often pushed into the back to provide stability as the mortar set. These buildings were built with lime mortar which hardened very slowly. Hydraulic limes were not unknown but they were less common and more expensive. In addition they often set too quickly resulting in high waste on site.


Lime mortars were common until the 1930s, in some parts of the UK, even later. Limestone or chalk was burnt with coal to form Quicklime. The burnt lime is known as lump lime. The Quicklime was then slaked with water and then mixed with fine aggregates (nowadays sand) to form mortar. It could take many months for a lime plaster to fully set. Then process is known as carbonation. Some limes have a hydraulic set (a bit like a weak cement). This could be induced by adding pozzolans which contain silica. Another option was to use a lime which naturally contains silicas (usually a proportion of clay). A hydraulic ‘set’ is quicker and stronger than carbonation. Some of the very strong hydraulic limes are not dissimilar to modern cement; made of course, from chalk and clay.

During the 1930s and 1940s cement mortars gradually replaced lime ones. Lime was often added to the mix to improve its working and qualities and durability. More detail can be found lower down the page.


In the early 1900s period joints were usually finished flush or slightly recessed.  Where very good quality bricks were used the joints were often only 8mm, or even less. This, together with the use of brick dust in the mortar, meant that the mortar had very little affect on a building’s appearance. Working-class housing was usually pointed in a lime mortar which included local industrial waste products as fine aggregate. Perhaps ash was the most common. The photos below show three examples of good quality 19th century brickwork.

Tuck pointing was usually reserved for the best quality work. Tuck pointing is basically in two parts, a bedding mortar often containing aggregates to match the colour of the bricks or stonework, and a thin ribbon of lime pointing to finish the joint. From a distance a wall that is tuck pointed appears to be finely jointed.  Examples of tuck pointing can be found under the Walls section of this web site.

Cavity walls

In the latter part of the 19th century a number of houses were built with cavity walls. It was not, however, until the 1920s that this became the accepted form of construction. Cavity walls were cheaper to build than their solid wall counterparts. In addition they offer improved thermal insulation and better weather protection. Most walls comprised two half-brick leaves with a 50mm cavity. The two halves of the wall were tied at regular intervals with steel or wrought iron wall ties. The external leaf of brickwork was laid in facing bricks, the internal leaf in commons. A few early cavity walls had an external leaf one brick thick and, in some early forms of construction, the DPC ran right across the cavity.

DPCs (to prevent rising damp) were in common use by the early 1900s. They could be made from lead, pitch, asphalt and slate. Not until the mid 1920s did vertical DPCs become a standard detail around openings.

1930s to 1960s

During this period cavity walls changed little. Mortars gradually became cement-based rather than lime-based because the faster setting mortar meant faster construction. Blockwork became a common material for the inner leaf of cavity walls – the blocks were usually made with an aggregate of stone or industrial waste (clinker and breeze were common). A few houses, usually Modernist-style houses with a rendered finish, were built with walls of solid blockwork (i.e. non cavity).

Note that during the 1950s and early 1960s several thousand houses were built in non-traditional construction. These were often constructed using precast frames or panels; in some cases insitu panels. Some systems were based on timber. For more information go to the System Building section of the web site.

1970s to 1980s

In the 1970s insulation standards slowly improved. A maximum ‘U’ value of 1.70 was introduced in 1972 (a measure of a the wall’s ability to transmit heat – explained further in the Walls section). Achieving this standard was relatively easy; a brick external leaf, a 50mm cavity, and a dense block inner leaf finished with 13mm lightweight plaster, just made the 1.7 threshold. In 1980 the maximum U value dropped to 1; this required lightweight blockwork in the inner leaf. From this period to the present day most lightweight blocks have been made from aerated concrete. They were (and still are) made from cement, lime, sand, pulverised fuel ash and aluminium powder.  Once these materials are mixed with hot water the aluminium powder reacts with the lime to form millions of tiny pockets of hydrogen.  However, there are several other materials for blockwork which have enjoyed brief popularity. These include concrete blocks faced with insulation, hollow blocks containing polystyrene granules and blocks made from pumice or no-fines concrete.

Modern cavity walls

In the 1990s the maximum U value dropped to 0.45; this normally required a very thick lightweight inner leaf or cavity insulation. There are three common options, most of which require lightweight or aerated blocks in the inner leaf. These are:

  • a clear cavity with an insulated dry lining
  • insulation boards which partially fill the cavity
  • insulation batts which fill the cavity.

It is still possible to build solid walls – but this is impractical using brick. Only aerated concrete will give acceptable levels of insulation.

At the time of writing (2006), U values have to less than 0.3 so a modern cavity wall has a ‘U’ value some 5 or 6 times better than its 1920s counterpart. In the above examples slightly thicker insulation will give a U value of 0.30. In modern construction cavity widths have increased well beyond the 50mm common 80 years ago. A 50mm clear gap is required if board insulation is used. This commonly requires a cavity 90mm wide.

Wall Ties

Wall ties are now mostly stainless steel. There are various patterns; the washer shown below is to hold insulation boards in position against the inner leaf. These particular ties are all made by Ancon.

Modern mortars

Modern mortars are made from cement and sand. Hydrated lime (i.e. bagged lime) is often introduced into the mix to give it a more plastic feel and to make it more ‘workable’.  Lime also improves the mortar’s ability to cope with thermal and moisture movement. In recent years the use of pre-mixed mortars has become common. These are delivered to site in sealed containers, ready for use. They usually contain a retarder so they remain usable for 36 – 48 hours or so. At the end of this period they develop their strength in the same way as normal mortars.

The face of the joint may be finished in a number of ways – the three most common are shown below. Tooled joints (where the mortar is pressed against the brickwork) offer the best weather protection because the tooling smoothes and compresses the joint.

This is a copy of an older ‘hand out’ on evolution – you may find it useful.The images are pre-publication proofs from ‘House Inspector’.

3 Ground Floors

Early Timber Floors

Most houses at the end of the Victorian period (1900) were built with suspended ground floors. There were exceptions to this. Many houses had ground floors constructed with stone or clay flags; basements too were covered with flags.  These were laid on a bed of ashes or directly onto compacted earth. Houses without basements usually had a scullery at the back of the house, often in a rear extension. Most sculleries had solid floors – they were used for washing and were likely to stay wet for long periods. The scullery floor was often 6 inches or so (150mm) below the main house floor in case of leaks or flooding. Some of these solid floors were made from concrete.

A typical suspended timber floor from about 1900 comprises a series of joists supported by external and internal loadbearing walls and covered with floorboards.  Deep joists were expensive (they still are) and to reduce joist size there were usually intermediate supports known as sleeper walls. These are small walls in rough stone or brickwork built directly on the ground or on small foundations. In practice, ground-floor joists are often half the depth of those used in upper floors where, of course, such intermediate support is not possible.

The joists are typically 100mm x 50mm and are usually at 400mm centres or so (16inches). To ventilate the sub-floor void terra cotta or cast iron air bricks were built-in to the external walls. In practice ventilation was not always effective, partly because there were not enough vents and partly because these houses were terraced. This meant that there were only two external walls. In addition, the sleeper walls were not always honeycombed (i.e. with ventilation gaps); this impeded cross ventilation.

Towards end of the Victorian period DPCs, often formed in brittle materials such as slate, were becoming common (but by no means universal). These helped protect the joist ends from rising damp.

In practice such floors often give rise to expensive maintenance problems due to poor design and varying standards of workmanship. They were generally badly ventilated, often prone to flooding (the ground level under the floor was often lower than the ground outside), and the joist ends are always at risk because they are normally only protected by a half-brick thickness of wall.

Some houses had concrete floors in the hallways, or maybe just in the lobby by the front door. These were usually covered with decorative tiles laid in mortar on a concrete slab (left).

The 1920s

During the first 20 years of the century suspended timber floors changed. A number of improvements were introduced, mostly damp related. In the graphic below note that the entire floor is separated from the substructure by the DPCs. In addition, the bare earth is covered with a concrete slab (often referred to as an ‘oversite’) which is at, or above, external ground level to prevent the build up of water.  The slab also prevents growth of vegetation. The floor joists are supported by honeycombed sleeper walls, through which air can pass easily, and the joists do not touch the external wall. Because most of these houses were detached or semi-detached, rather than terraced, the underfloor void is relatively easy to ventilate.

Ground bearing concrete floors – 1950s

Concrete ground floors were not unknown in the 1930s but they became more common in the 1950s because of the post War restrictions on imported timber (restrictions lasted for nearly 10 years). The floor is basically a bed of concrete, supported by the ground directly beneath it, and quite independent of the surrounding walls.

A typical floor from the 1950s might comprise a layer of hardcore (stone or broken brick), a concrete slab probably 100 to 125mm thick and the floor finish. This is often timber to disguise the nature of the floor, or, in cheaper construction, thermoplastic tiles laid in bitumen adhesive. Some floors, by no means all, contained damp proof membranes, usually liquid based.

In many houses the only barrier to rising damp was the bitumen bedding material under the wood blocks or thermoplastic tiles. Thermoplastic tiles were first produced in the UK just after the Second World War. The tiles were made from a mixture of resin binders, mineral fillers, asbestos and pigments. Most were 9 inches square (225mm). Early tiles were quite brittle. Asbestos vinyl tiles were introduced in the mid 1950s; they were made in much the same way but they were more flexible.

Ground bearing concrete floors – 1960s to 1990s

From the mid 1960s to the mid 1990s a typical concrete floor comprised a layer of hardcore, a polythene damp proof membrane laid on a thin bed of sand (to prevent puncturing), and a floor screed.

Hardcores varied in quality – many have since proved to be totally unsuitable. In the mid 1960s polythene damp proof membranes were introduced and became an accepted form of damp proofing.  This barrier was usually laid below the concrete slab. DPMs on top of the slab, i.e. sandwiched under the screed, were also common and usually in liquid form, e.g. hot bitumen, or cold bitumen in solution.  Liquid DPMs gave the best protection but were more expensive. The concrete slab was usually 100 to 125mm thick. In certain situations, i.e. where the ground was uneven or where there were soft spots below the slab, it might be reinforced with a mesh.

The floor screed provided a smooth finish suitable for carpets or tiling. It was laid towards the completion of the building prior to hanging the doors and fixing the skirtings. It was (and is) is a mixture of cement and course sand (typically one part cement to three or four parts sand) mixed with the minimum amount of water and laid to a thickness of 38-50mm. A few floors had a DPM formed in 20mm asphalt. This could be trowelled to a level finish and precluded the need for a separate screed.

Modern Concrete floors

Since the mid 1990s the Building Regulations have required insulation in ground floors.  A variety of manufacturers produce a range of rigid insulation boards which can be laid above or below the slab. Some of the boards have a closed-cell structure and are impervious to both water and vapour.  They can therefore be laid under the DPM (the DPM is still necessary to prevent moisture rising between the board joints and penetrating the slab). Where boards are laid under the DPM blinding is not always necessary. Typical construction is shown below.

Chipboard flooring

In modern construction chipboard floating floors have become a common alternative to a sand/cement screed. Chipboard and strand board are both very sensitive to moisture and a vapour control layer is normally required under the boarding to prevent drying construction water (i.e. in the concrete) affecting the floor. This membrane is in addition to the DPM below the slab. The tongued & grooved boarding has glued joints and normally sits on a resilient layer of insulation; a perimeter gap of 10mm or so allows for moisture and thermal expansion. This gap is covered by the skirting.

Suspended concrete floors

In certain conditions the use of a ground bearing slab is not suitable. In these situations it is common to find a suspended concrete floor.  In fact, nowadays, many developers prefer to use suspended concrete floors in all situations because of the perceived risks of ground bearing floors. Until the 1970s these floors were often constructed from insitu concrete but they were slow to construct and very expensive. Nowadays, the floors are usually made from a series of inverted ‘T’ beams, 150-200mm thick, with a concrete block infill. The two most popular finishes are screed or particle board, both laid on insulation.

Nowadays the Building regulations require that the underfloor space is vented; before 2004 it was only necessary to ventilate the space if the ground was not well drained or if there was a risk of gas build-up. DPMs are not required as long as minimum recommended gaps between floor soffits and sub-soil are maintained.

Modern timber floors

In modern construction timber floors are, once again, becoming popular. The construction is similar to that of 70 years ago although there are a few differences:

  • joists will be supported on hangers rather than built into the walls.
  • timbers are nowadays usually treated against rot and insect attack.
  • rules for ventilation are more onerous than in the past.
  • most floors will be finished with chipboard and floors will be insulated.

This is a copy of an older ‘hand out’ on evolution – you may find it useful. It includes two pages on upper floors. The images are pre-publication proofs from ‘House Inspector’.

4 Upper Floors


The upper floor of a modern house is not that much different from its 1800 counterpart. In other words it comprises a series of timber joists (there are modern alternatives) covered with some form of floor boarding. Nowadays we always expect to find a ceiling although, 150 years ago, the joist soffit was often left open in working-class housing. In modern construction the size and spacing of the joists are subject to the Building Regulations. Before 1965 they were mostly controlled by Model Bye-Laws or accepted building practice.

Note that this brief introduction does not include the construction of floors between flats. Information on this can be found under the Floors section of this web site.

Late 19th century

At the end of the 19th century a typical well-built terraced house would have an upper floor constructed from 8″ by 2″ (200 x 50mm) softwood floor joists fixed at 12″ to 16″ centres (300 to 400)mm. The joists were usually built in to the walls although occasionally wrought iron or brick corbels were used. Corbels were expensive but did ensure that joists on party walls did not penetrate the brickwork (better sound and fire protection) and that joists on external walls were protected by the full thickness of the wall (less chance of rot).

The floor was normally covered with square-edged softwood boards and finished with a lath and plaster ceiling – usually 3 coats of lime plaster. The direction of the joists can either be party wall to party wall, or front to back. The joists were trimmed around fireplaces and stair openings as shown in the graphic.  A half-barrel vault supported the hearth. Note that more information on fireplace construction can be found in the Heating section of this web site.

Larger properties may have had double floors, in other words a floor with a primary timber (or steel) beam running at right angles to the joists and supporting them mid span. An advantage of a double floor is that it keeps the floor depth to a minimum and provides all four walls with lateral restraint. Larger, more prestigious, properties sometimes had various types of tongued and grooved boards rather than square edged ones. These are shown further down the page.


In the 1930s the construction was much the same. Contemporary text books show a number of alternative methods of supporting the joists to suit a Model Bye-law of the time which required that no timber could be built within a half brick of the centre of a party wall. The bye-law also specified that all joists should rest upon a wall plate or steel bearing bar (to spread the load across the wall). In practice these bye-laws were often not adopted by local authorities or just ignored.  Text books also suggested that joist ends should be tarred or creosoted where they were built into walls.

‘Specification’ from 1931 provides some general guidance on the construction of upper floors (interestingly enough it does not mention the bye-law requirements). Single floors were normally thought to be acceptable for floor spans up to 16 feet; above that double floors were recommended.

Herringbone strutting was normally recommend at 6 feet intervals (1.8 metres). Unlike Victorian and Edwardian floors the hearth support was often in the form of insitu concrete reinforced with mesh rather than a half barrel vault.

1950s and 1960s

In the post War period timber imports were strictly controlled. Although some system-built houses had floors made from steel joists  most houses had fairly traditional upper floors, often with centres ‘stretched’ and joist sizes reduced, to save timber. In addition strutting was often omitted. Floor coverings were usually tongued and grooved softwood. Boarded ceilings replaced lath and plaster – fibre board, asbestos board and plasterboard (often small sheets – i.e. plasterboard lath) were all common. Joists were built-in or supported on hangers.

By the 1960s timber rationing was over and floor timbers reverted to pre-War sizes. The 1965 Building Regulations introduced tables for sizing floor joists and these remain much the same to this day. During the 1960s plasterboard became virtually the only material used for ceilings. The boarding was normally 10mm or 12.5mm thick (3/8inch or 1/2inch) with an artex or gypsum plaster finish.

Modern floors

The construction of modern upper floors is shown below. They differ from 1950s floors in three main ways: strapping is now required to restrain the external walls, joist hangers are almost obligatory (to prevent air leakage), and floor boards have largely been replaced by chipboard or strand board. Modern ceilings are still nearly always formed in plasterboard.  Nowadays plasterboard lath is rare; the construction usually consists of large sheets of 15mm plasterboard, screwed to joists or to resilient bars, and then taped and painted.

In recent years the use of metal web joists and ‘I’ joists has become more common. In principle these are no different from traditional ‘cut’ joists. One advantage is that they are capable of increased spans. The use of metal web joists also precludes the need for potentially damaging joist notching.


In flats the floors separate dwellings and, therefore, must provide good fire protection and resistance to the passage of impact and airborne sound. The methods of construction shown above are not suitable. Modern options and a brief historical overview can be found in the Floors section of this web site.

5 Roof Structure


During the 19th century the construction of domestic roofs changed little. In the late 1800s timbers were cut by machine rather than by hand, and fixings in the forms of nails, screws and bolts were cheaper and more readily available, but the nature of the structure was much the same as it had been 100 years earlier.


A typical roof comprised a series of sloping timbers known as rafters fixed, at the top to a ridge board, and at the bottom to a wall plate. Ceiling joists supported the ceiling and acted as a tie to the rafters – to stop the rafter feet from spreading. A binder running at right angles to the ceiling joists could be added to help prevent deflection in the joists. In some houses the binder was connected to the ridge by a hanger, again to prevent deflection.

This type of construction could be adapted for larger roofs. The roof shown on the right is the same in principle although there is an additional timber known as a purlin which prevents the rafters from sagging mid span.   The purlin is supported by the gable-end walls (party walls in mid-terraced houses) and is sometimes strutted from an internal loadbearing wall (and sometimes the gable walls) to a provide additional support.

The feet of the rafters were designed to provide a roof overhang or to finish flush with the wall. A fascia board at the feet of the rafters finished off the roof and supported the cast iron or, in a few cases, timber guttering.

Some very large houses with big rooms did not have an internal loadbearing wall in an appropriate position. Other ways had to be found of supporting the purlins mid span. King and Queen post trusses could be used in this instance. These were also widely used in factories and warehouses where large uninterrupted spaces were required.

Nearly all the roofs built before 1940 would have been based on the closed couple or purlin design. Sometimes the style was adapted slightly. A hipped roof (below) is a different shape but the arrangement of the timbers is much the same. Larger examples had strutted purlins; larger examples still, had trusses – usually one full truss spanning front to back, and a half truss supporting the end (hip) purlin.

Post War Years

During the War 500,000 homes were damaged or destroyed. In the post War period there was a massive building programme not just to rebuild these damaged homes but also to continue the slum clearance work of the 1930s. But, at the same time, there was a chronic (it lasted for nearly 10 years) shortage of materials. In an attempt to avoid economic disaster the government placed strict limits on the import of materials. Timber was in short supply and new techniques had to be found. At ground floor level timber was saved by building floors in concrete. This was not a practical solution for roofs (apart from a few flat roofs in system-built houses) so techniques were developed which would reduce the amount of timber used in a roof. The TRADA truss is basically a lightweight version of the trusses shown above. They did away with the need for internal loadbearing walls upstairs and allowed for smaller section rafters – often at slightly wider centres. They were common during the 1950s.

Trussed rafters

The TRADA truss was relatively short lived.Most modern roofs are constructed from trussed rafters; they have been popular since the 1960s. The most common pattern is the Fink or ‘W’ truss designed for symmetrical double-pitch roofs although there are a variety of shapes suitable for most roof designs.  The trussed rafters are prefabricated and delivered to site ready for lifting onto the supporting walls, although occasionally you will find the entire roof structure assembled on the ground and lifted into place by crane.

The timbers, which are typically 80 x 40mm in section, are butt-jointed and held together by special plates (first introduced to the UK in the mid 1960s) which are pressed into position by machine.  Nowadays the timber are normally pre-treated to guard against rot and insect attack.

Trussed rafters offer several advantages when compared to traditional roofing methods.

  • No internal support is required from loadbearing partitions.
  • Spans of up to about 12 metres can easily be achieved.
  • They offer vary fast construction.
  • Skilled labour is not required.
  • They are relatively cheap.
  • They can be designed with very shallow pitches.

Perhaps their major disadvantage is that use of the roof space for storage (when using normal trusses) is severely limited due to the nature of the timbers. When the trusses are in position additional timbers (braces) need to be added to produce a strong, rigid roof structure. These are explained elsewhere on this web site.

New ‘cut’ or traditional roofs are sometimes still found but they tend to be one-off dwellings often with living accommodation in the roof space.

Modern trussed rafters and traditional roofs are both supported on softwood wall plates bedded in mortar on the inner leaf of the cavity wall. It’s normal practice to strap the roofs to the blockwork inner leaf to prevent them lifting or moving in high winds. Modern roofs are normally ventilated to help minimise condensation. This is usually done by installing air vents at the eaves. There are other methods and these are explained elsewhere on this web site.

This is a copy of an older ‘hand out’ on evolution – you may find it useful. The images are pre-publication proofs from ‘House Inspector’.

6 Windows

Early windows were usually fixed lights or side-hung casements. All the examples below are mid to late 17th century. The timber window on the far left is part of a timber framed house built in Bristol’s dock area. The second example shows a stone building (c1690) with timber window frames glazed with diamond shaped leaded glass (small panes of glass were much cheaper than large sheets). A hinged, wrought iron casement has been fitted into the right hand section of window. The window on the right has a fixed light directly glazed into the stonework and a hinged iron casement.

In the late 17th century sash windows were introduced to Britain. These windows were usually still formed in small panes because of the limitations of glass technology. The timber sections were quite thick and the window was set flush with the face of the brick or stonework (left hand photo – about 1710). The windows were controlled with lead (later iron) weights which counter-balanced the weight of the sashes. During the Georgian period the glazing bars became thinner and thinner and, at the same time, the windows were set in rebates which hid the box frames. In houses with thick walls the inner reveals often contained shutters (centre photo – about 1800). From the late 18th century onwards it became fashionable (for the wealthy at least) to have full length windows on the first floor leading onto a wrought and cast iron balcony.

Windows are visually important architectural elements. For example windows were integral to the architectural philosophy of the Georgian era, where their proportions were closely defined in relation to the dictates of symmetry. During the Georgian era window tax was introduced. This was levied on the number of windows in a house and goes some way towards explaining why some windows from this era were blocked up. In the middle of the 19th century this tax was dropped. This change was accompanied by increasing concern with daylight and ventilation, which the Victorians associated with good health. Consequently there was a move towards stipulating minimum window sizes. Towards the end of the Victorian period improvements in glass technology precluded the need for glazing bars altogether.

In the 1920s top hung and side hung casements became popular. The example on the left is from about 1920 and is a crude example of Queen Anne revival sash windows; they were popular during the Edwardian period and were characterised by having a small-paned top sash over a single paned bottom sash – white paint was de rigeur. The right-hand example is from the mid 1930s; casement windows with top hung leaded top-lights (often glazed with stained glass).

Metal windows, introduced in the very late 19th century, were very common until the 1970s. Early windows were plain mild steel; from the 1930s they were mostly galvanised. As houses became better insulated and less well ventilated their shortcomings became more obvious – the cold inner face of the frames resulted in condensation.

In the post war period high rise housing required new approaches to window styles. Traditional sash windows could not possibly withstand the turbulence and exposure at high levels, and casement windows would be impossible to clean. A common form of window was the horizontal pivot window. These could be made from galvanised metal, timber or aluminium and could be cleaned from the inside.

Aluminium windows (below left) became very popular during the 1970s but, in recent years, have almost completely been eclipsed by plastic. Aluminium windows, like galvanised metal, are good conductors of heat and condensation is always likely to be a problem. In the 1970s a policy of rehabilitating older properties replaced slum clearance and high rise construction. In many cases budgets were not adequate and houses, originally refurbished for 30 years or so, required substantial extra investment after less than 10 years. One example of cost cutting was the louvre window (below right). These were cheap to make, just requiring a simple softwood frame, but were draughty, provided inadequate ventilation in the Summer, and could not readily be used as a means of escape. Other rehab and new houses were fitted with ‘standard’ timber windows. There were hundreds of styles (below middle). These windows were cheap but mostly made from poor quality timber.

Nowadays, windows are usually made from imported softwoods and hardwoods, or from plastic. There are literally hundreds of styles to choose from. The public has become accustomed to renewing windows, almost as fashion accessories, and often well in advance of their likely life. Because of this, replacement windows has become a very big, but in some cases completely unnecessary, business. The design of windows and the choice of material used may be controlled by planning authorities in conservation areas. Plastic replacement windows are a focus for concern in such areas because they affect character and appearance. Even outside conservation areas the replacement of wooden sash windows will have a significant visual affect on say a street of Victorian terraced houses (below right). The windows on the far right are mock Georgian; the glazing bars are sandwiched between the double glazing.

Bearing Capacity Technical Guidance

Bearing capacity of soil is the value of the average contact pressure between the foundation and the soil which will produce shear failure in the soil. Ultimate bearing capacity is the theoretical maximum pressure which can be supported without failure. Allowable bearing capacity is what is used in geotechnical design, and is the ultimate bearing capacity divided by a factor of safety.

Theoretical (Ultimate) and allowable bearing capacity can be assessed for the following:

  • Shallow Foundations
    • strip footings
    • square footings
    • circular footings
  • Deep foundations
    • end bearing
    • skin friction

For comprehensive examples of bearing capacity problems see:

  • Bearing Capacity Examples

Allowable Bearing Capacity

Qa   =    Qu                                 Qa = Allowable bearing capacity  (kN/m2) or (lb/ft2)


Qu = ultimate bearing capacity (kN/m2) or (lb/ft2)                *See below for theory
F.S. = Factor of Safety

Ultimate Bearing Capacity for Shallow Foundations

Terzaghi Ultimate Bearing Capacity Theory


Qu = c Nc + g D Nq + 0.5 g B Ng
= Ultimate bearing capacity equation for shallow strip footings, (kN/m2) (lb/ft2)

Qu = 1.3 c Nc + g D Nq + 0.4 g B Ng
= Ultimate bearing capacity equation for shallow square footings, (kN/m2) (lb/ft2)

Qu = 1.3 c Nc + g D Nq + 0.3 g B Ng
= Ultimate bearing capacity equation for shallow circular footings, (kN/m2) (lb/ft2)


c = Cohesion of soil (kN/m2) (lb/ft2),
g = effective unit weight of soil (kN/m3) (lb/ft3),  *see note below
D = depth of footing (m) (ft),
B = width of footing (m) (ft),
Nc=cotf(Nq – 1),                                             *see typical bearing capacity factors
Nq=e2(3p/4-f/2)tanf / [2 cos2(45+f/2)],         *see typical bearing capacity factors
N g=(1/2) tanf(kp /cos2 f – 1),                         *see typical bearing capacity factors
e = Napier’s constant = 2.718…,
kp = passive pressure coefficient, and
f = angle of internal friction (degrees).

Effective unit weight, g, is the unit weight of the soil for soils above the water table and capillary rise. For saturated soils, the effective unit weight is the unit weight of water, gw, 9.81 kN/m3 (62.4 lb/ft3), subtracted from the saturated unit weight of soil. Find more information in the foundations section.

Meyerhof Bearing Capacity Theory Based on Standard Penetration Test Values

Qu = 31.417(NB + ND)      (kN/m2)                        (metric)

Qu =   NB    +   ND            (tons/ft2)                       (standard)
10           10

For footing widths of 1.2 meters (4 feet) or less

Qa =   11,970N               (kN/m2)                        (metric)

Qa =   1.25N                   (tons/ft2)                       (standard)

For footing widths of 3 meters (10 feet) or more

Qa =   9,576N                 (kN/m2)                        (metric)

Qa =   N                          (tons/ft2)                       (standard)

N = N value derived from Standard Penetration Test (SPT)
D = depth of footing (m) (ft), and
B = width of footing (m) (ft).

Note:  All Meyerhof equations are for foundations bearing on clean sands. The first equation is for ultimate bearing capacity, while the second two are factored within the equation in order to provide an allowable bearing capacity. Linear interpolation can be performed for footing widths between 1.2 meters (4 feet) and 3 meters (10 feet). Meyerhof equations are based on limiting total settlement to 25 cm (1 inch), and differential settlement to 19 cm (3/4 inch).


Ultimate Bearing Capacity for Deep Foundations (Pile)

Qult = Qp + Qf


Qult = Ultimate bearing capacity of pile, kN (lb)
Qp = Theoretical bearing capacity for tip of foundation, or end bearing, kN (lb)
Qf = Theoretical bearing capacity due to shaft friction, or adhesion between foundation shaft and soil, kN (lb)


End Bearing (Tip) Capacity of Pile Foundation

Qp = Apqp


Qp = Theoretical bearing capacity for tip of foundation, or end bearing, kN (lb)
Ap = Effective area of the tip of the pile, m2 (ft2)
For a circular closed end pile or circular plugged pile; Ap = p(B/2)2 m2 (ft2)
qp = gDNq
= Theoretical unit tip-bearing capacity for cohesionless and silt soils, kN/m2 (lb/ft2)
qp = 9c
= Theoretical unit tip-bearing capacity for cohesive soils, kN/m2 (lb/ft2)
g = effective unit weight of soil, kN/m3 (lb/ft3),                                *See notes below
D = Effective depth of pile, m (ft), where D < Dc,
Nq = Bearing capacity factor for piles,
c = cohesion of soil, kN/m2 (lb/ft2),
B = diameter of pile, m (ft), and
Dc = critical depth for piles in loose silts or sands m (ft).
Dc = 10B, for loose silts and sands
         Dc = 15B, for medium dense silts and sands
         Dc = 20B, for dense silts and sands


Skin (Shaft) Friction Capacity of Pile Foundation

Qf = Afqf       for one homogeneous layer of soil

Qf = pSqfL    for multi-layers of soil


Qf = Theoretical bearing capacity due to shaft friction, or adhesion between foundation shaft and soil, kN (lb)
Af = pL; Effective surface area of the pile shaft, m2 (ft2)
qf = ks tan d = Theoretical unit friction capacity for cohesionless soils, kN/m2 (lb/ft2)
qf = cA + ks tan d = Theoretical unit friction capacity for silts, kN/m2 (lb/ft2)
qf = aSu = Theoretical unit friction capacity for cohesive soils, kN/m2 (lb/ft2)
p = perimeter of pile cross-section, m (ft)
for a circular pile; p = 2p(B/2)
for a square pile; p = 4B
L = Effective length of pile, m (ft)                                              *See Notes below
a = 1 – 0.1(Suc)2 = adhesion factor, kN/m2 (ksf), where Suc < 48 kN/m2 (1 ksf)
a =    1    [0.9 + 0.3(Suc – 1)] kN/m2, (ksf) where Suc > 48 kN/m2, (1 ksf)
Suc = 2c = Unconfined compressive strength , kN/m2 (lb/ft2)
cA = adhesion
= c for rough concrete, rusty steel, corrugated metal
0.8c < cA < c for smooth concrete
0.5c < cA < 0.9c for clean steel
c = cohesion of soil, kN/m2 (lb/ft2)
d = external friction angle of soil and wall contact (deg)
f = angle of internal friction (deg)
s = gD = effective overburden pressure, kN/m2, (lb/ft2)
k = lateral earth pressure coefficient for piles
g = effective unit weight of soil, kN/m3 (lb/ft3)                    *See notes below
B = diameter or width of pile, m (ft)
D = Effective depth of pile, m (ft), where D < Dc
Dc = critical depth for piles in loose silts or sands m (ft).
Dc = 10B, for loose silts and sands
         Dc = 15B, for medium dense silts and sands
         Dc = 20B, for dense silts and sands
S = summation of differing soil layers (i.e. a1 + a2 + …. + an)
Notes: Determining effective length requires engineering judgment. The effective length can be the pile depth minus any disturbed surface soils, soft/ loose soils, or seasonal variation. The effective length may also be the length of a pile segment within a single soil layer of a multi layered soil. Effective unit weight, g, is the unit weight of the soil for soils above the water table and capillary rise. For saturated soils, the effective unit weight is the unit weight of water, gw, 9.81 kN/m3 (62.4 lb/ft3), subtracted from the saturated unit weight of soil.


Meyerhof Method for Determining  qp and qf in Sand

Theoretical unit tip-bearing capacity for driven piles in sand, when  D  > 10:
     qp = 4Nc  tons/ft2                      standard

Theoretical unit tip-bearing capacity for drilled piles in sand:

     qp = 1.2Nc  tons/ft2                   standard

Theoretical unit friction-bearing capacity for driven piles in sand:

     qf =  N   tons/ft2                         standard

Theoretical unit friction-bearing capacity for drilled piles in sand:

     qf =  N   tons/ft2                         standard


D = pile embedment depth, ft
B = pile diameter, ft
Nc = Cn(N)
Cn = 0.77 log  20  

N = N-Value from SPT test
s = gD = effective overburden stress at pile embedment depth,  tons/ft2
= (g – gw)D = effective stress if below water table,  tons/ft2
g = effective unit weight of soil,  tons/ft3
gw = 0.0312 tons/ft3 = unit weight of water

Examples for determining allowable bearing capacity

Example #1: Determine allowable bearing capacity and width for a shallow strip footing on cohesionless silty sand and gravel soil. Loose soils were encountered in the upper 0.6 m (2 feet) of building subgrade. Footing must withstand a 144 kN/m2 (3000 lb/ft2) building pressure.


  • bearing pressure from building = 144 kN/m2 (3000 lbs/ft2)
  • unit weight of soil, g = 21 kN/m3 (132 lbs/ft3)  *from soil testing, see typical g values
  • Cohesion, c = 0                                               *from soil testing, see typical c values
  • angle of Internal Friction, f = 32 degrees         *from soil testing, see typical f values
  • footing depth, D = 0.6 m (2 ft)                         *because loose soils in upper soil strata



Try a minimal footing width, B = 0.3 m (B = 1 foot).

Use a factor of safety, F.S = 3. Three is typical for this type of application. See factor of safety for more information.

Determine bearing capacity factors Ng, Nc and Nq. See typical bearing capacity factors relating to the soils’ angle of internal friction.

  • Ng = 22
  • Nc = 35.5
  • Nq = 23.2

Solve for ultimate bearing capacity,

Qu = c Nc + g D Nq + 0.5 g B Ng                                *strip footing eq.

Qu = 0(35.5) + 21 kN/m3(0.6m)(23.2) + 0.5(21 kN/m3)(0.3 m)(22)                 metric
Qu = 362 kN/m2

Qu = 0(35.5) + 132lbs/ft3(2ft)(23.2) + 0.5(132lbs/ft3)(1ft)(22)                          standard
Qu = 7577 lbs/ft2

Solve for allowable bearing capacity,

Qa =   Qu    

Qa =  362 kN/m2  = 121 kN/m2                                          not o.k.                 metric
Qa =  7577lbs/ft2  = 2526 lbs/ft2                                          not o.k.                 standard 

Since Qa < required 144 kN/m2 (3000 lbs/ft2) bearing pressure, increase footing width, B or foundation depth, D to increase bearing capacity.

Try footing width, B = 0.61 m (B = 2 ft).

Qu = 0 + 21 kN/m3(0.61 m)(23.2) + 0.5(21 kN/m3)(0.61 m)(22)                      metric
Qu = 438 kN/m2

Qu = 0 + 132 lbs/ft3(2 ft)(23.2) + 0.5(132 lbs/ft3)(2 ft)(22)                                standard
Qu = 9029 lbs/ft2


Qa =   438 kN/m2   = 146 kN/m2          Qa > 144 kN/m2            o.k.                   metric

Qa =   9029 lbs/ft2 = 3010 lbs/ft2           Qa > 3000 lbs/ft2           o.k.                  standard


Footing shall be 0.61 meters (2 feet) wide at a depth of 0.61 meters (2 feet) below ground surface.Many engineers neglect the depth factor (i.e. D Nq = 0) for shallow foundations. This inherently increases the factor of safety. Some site conditions that may negatively effect the depth factor are foundations established at depths equal to or less than 0.3 meters (1 feet) below the ground surface, placement of foundations on fill, and disturbed/ fill soils located above or to the sides of foundations.




Example #2: Determine allowable bearing capacity of a shallow, 0.3 meter (12-inch) square isolated footing bearing on saturated cohesive soil. The frost penetration depth is 0.61 meter (2 feet). Structural parameters require the foundation to withstand 4.4 kN (1000 lbs) of force on a 0.3 meter (12-inch) square column.


  • bearing pressure from building column = 4.4 kN/ (0.3 m x 0.3 m) = 48.9 kN/m2
  • bearing pressure from building column = 1000 lbs/ (1 ft x 1 ft) = 1000 lbs/ft2
  • unit weight of saturated soil, gsat= 20.3 kN/m3 (129 lbs/ft3)            *see typical g values
  • unit weight of water, gw= 9.81 kN/m3 (62.4 lbs/ft3)                        *constant
  • Cohesion, c = 21.1 kN/m2 (440 lbs/ft2)                *from soil testing, see typical c values
  • angle of Internal Friction, f = 0 degrees                *from soil testing, see typical f values
  • footing width, B = 0.3 m (1 ft)



Try a footing depth, D = 0.61 meters (2 feet), because foundation should be below frost depth.

Use a factor of safety, F.S = 3. See factor of safety for more information.

Determine bearing capacity factors Ng, Nc and Nq. See typical bearing capacity factors relating to the soils’ angle of internal friction.

  • Ng = 0
  • Nc = 5.7
  • Nq = 1

Solve for ultimate bearing capacity,

Qu = 1.3c Nc + g D Nq + 0.4 g B Ng                                  *square footing eq.

Qu =1.3(21.1kN/m2)5.7+(20.3kN/m3-9.81kN/m3)(0.61m)1+0.4(20.3kN/m3-9.81kN/m3)(0.3m)0
Qu = 163 kN/m2                                                                                       metric

Qu = 1.3(440lbs/ft2)(5.7) + (129lbs/ft3 – 62.4lbs/ft3)(2ft)(1) + 0.4(129lbs/ft3 – 62.4lbs/ft3)(1ft)(0)
Qu = 3394 lbs/ft2                                                                                      standard

Solve for allowable bearing capacity,

Qa =   Qu    

Qa =   163 kN/m2   = 54 kN/m2             Qa > 48.9 kN/m2         o.k.          metric
Qa =    3394lbs/ft2   = 1130 lbs/ft2         Qa > 1000 lbs/ft2         o.k.          standard


The 0.3 meter (12-inch) isolated square footing shall be 0.61 meters (2 feet) below the ground surface. Other considerations may be required for foundations bearing on moisture sensitive clays, especially for lightly loaded structures such as in this example. Sensitive clays could expand and contract, which could cause structural damage. Clay used as bearing soils may require mitigation such as heavier loads, subgrade removal and replacement below the foundation, or moisture control within the subgrade.




Example #3: Determine allowable bearing capacity and width for a foundation using the Meyerhof Method. Soils consist of poorly graded sand. Footing must withstand a 144 kN/m2(1.5 tons/ft2) building pressure.


  • bearing pressure from building = 144 kN/m2 (1.5 tons/ft2)
  • N Value, N = 10 at 0.3 m (1 ft) depth                          *from SPT soil testing
  • N Value, N = 36 at 0.61 m (2 ft) depth                        *from SPT soil testing
  • N Value, N = 50 at 1.5 m (5 ft) depth                          *from SPT soil testing


Try a minimal footing width, B = 0.3 m (B = 1 foot) at a depth, D = 0.61 meter (2 feet). Footings for single family residences are typically 0.3m (1 ft) to 0.61m (2ft) wide. This depth was selected because soil density greatly increases (i.e. higher N-value) at a depth of 0.61 m (2 ft).

Use a factor of safety, F.S = 3. Three is typical for this type of application. See factor of safety for more information.

Solve for ultimate bearing capacity

Qu = 31.417(NB + ND)      (kN/m2)                          (metric)

Qu =   NB    +   ND            (tons/ft2)                         (standard)
10           10

Qu = 31.417(36(0.3m) + 36(0.61m)) = 1029 kN/m2    (metric)

Qu =   36(1 ft)   +   36(2 ft)   = 10.8 tons/ft2                 (standard)
10                10

Solve for allowable bearing capacity,

Qa =   Qu    

Qa =  1029 kN/m2  = 343 kN/m2    Qa > 144 kN/m2      o.k.    (metric)
Qa =  10.8 tons/ft2  = 3.6 tons/ft2     Qa > 1.5 tons/ft2      o.k.    (standard) 


Footing shall be 0.3 meters (1 feet) wide at a depth of 0.61 meters (2 feet) below the ground surface. A footing width of only 0.3 m (1 ft) is most likely insufficient for the structural engineer when designing the footing with the building pressure in this problem.




Example #4: Determine allowable bearing capacity and diameter of a single driven pile. Pile must withstand a 66.7 kN (15 kips) vertical load.


  • vertical column load = 66.7 kN (15 kips or 15,000 lb)
  • homogeneous soils in upper 15.2 m (50 ft); silty soil
    • unit weight, g = 19.6 kN/m3 (125 lbs/ft3) *from soil testing, see typical g values
    • cohesion, c = 47.9 kN/m2 (1000 lb/ft2)   *from soil testing, see typical c values
    • angle of internal friction, f = 30 degrees   *from soil testing, see typical f values
  • Pile Information
    • driven
    • steel
    • plugged end



Try a pile depth, D = 1.5 meters (5 feet)
Try pile diameter, B = 0.61 m (2 ft)

Use a factor of safety, F.S = 3. Smaller factors of safety are sometimes used if piles are load tested, or the engineer has sufficient experience with the regional soils.

Determine ultimate end bearing of pile,

Qp = Apqp
Ap = p(B/2)2 = p(0.61m/2)2 = 0.292 m2                                      metric
Ap = p(B/2)2 = p(2ft/2)2 = 3.14 ft2                                                        standard

qp = gDNq

g = 19.6 kN/m3 (125 lbs/ft3); given soil unit weight
f = 30 degrees; given soil angle of internal friction
B = 0.61 m (2 ft); trial pile width
D = 1.5 m (5 ft); trial depth, may need to increase or decrease depending on capacity
check to see if D < Dc
       Dc = 15B = 9.2 m (30 ft); critical depth for medium dense silts.
If D > Dc, then use Dc
Nq = 25; Meyerhof bearing capacity factor for driven piles, based on f

qp = 19.6 kN/m3(1.5 m)25 = 735 kN/m2                                    metric
qp = 125 lb/ft3(5 ft)25 = 15,625 lb/ft2                                          standard
Qp = Apqp = (0.292 m2)(735 kN/m2) = 214.6 kN                     metric
Qp = Apqp = (3.14 ft2)(15,625 lb/ft2) = 49,063 lb                      standard


Determine ultimate friction capacity of pile,

Qf = Afqf

Af = pL

p = 2p(0.61m/2) = 1.92 m                                                            metric
p = 2p(2 ft/2) = 6.28 ft                                                                 standard
L = D = 1.5 m (5 ft); length and depth used interchangeably. check Dc as above

Af = 1.92 m(1.5 m) = 2.88 m2                                                      metric   
Af = 6.28 ft(5 ft) = 31.4 ft2                                                           standard

qf = cA + ks tan d = cA + kgD tan d

k = 0.5; lateral earth pressure coefficient for piles, value chosen from Broms low density steel
g = 19.6 kN/m3 (125 lb/ft3); given effective soil unit weight. If water table, then g – gw
D = L = 1.5 m (5 ft); pile length. Check to see if D < Dc
Dc = 15B = 9.2 m (30 ft); critical depth for medium dense silts. If D > Dc, then use Dc
d = 20 deg; external friction angle, equation chosen from Broms steel piles
B = 0.61 m (2 ft); selected pile diameter
cA = 0.5c; for clean steel. See adhesion in pile theories above.
= 24 kN/m2 (500 lb/ft2)

qf = 24 kN/m2 + 0.5(19.6 kN/m3)(1.5m)tan 20 = 29.4 kN/m2      metric
qf = 500 lb/ft2 + 0.5(125 lb/ft3)(5ft)tan 20 = 614 lb/ft2                  standard

Qf = Afqf = 2.88 m2(29.4 kN/m2) = 84.7 kN                               metric
Qf = Afqf = 31.4 ft2(614 lb/ft2) = 19,280 lb                                  standard


Determine ultimate pile capacity,

Qult = Qp + Qf

Qult = 214.6 kN + 84.7 kN = 299.3 kN                                       metric
Qult = 49,063 lb + 19,280 lb = 68,343 lb                                      standard


Solve for allowable bearing capacity,

Qa =  Qult     

Qa   299.3 kN    = 99.8 kN;  Qa > applied load (66.7 kN)     o.k.     metric
Qa   68,343 lbs    = 22,781 lbs  Qa > applied load (15 kips)   o.k.     standard



A 0.61 m (2 ft) steel pile shall be plugged and driven 1.5 m (5 feet) below the ground surface. Many engineers neglect the skin friction within the upper 1 to 5 feet of subgrade due to seasonal variations or soil disturbance. Seasonal variations may include freeze/ thaw or effects from water. The end bearing alone (neglect skin friction) is sufficient for this case. Typical methods for increasing the pile capacity are increasing the pile diameter or increasing the embedment depth of the pile.



Example #5: Determine allowable bearing capacity and diameter of a single driven pile. Pile must withstand a 66.7 kN (15 kips) vertical load.


  • vertical column load = 66.7 kN (15 kips or 15,000 lb)
  • upper 1.5 m (5 ft) of soil is a medium dense gravelly sand
    • unit weight, g = 19.6 kN/m3 (125 lbs/ft3) *from soil testing, see typical g values
    • cohesion, c = 0                                        *from soil testing, see typical c values
    • angle of internal friction, f = 30 degrees   *from soil testing, see typical f values
  • soils below 1.5 m (5 ft) of soil is a stiff silty clay
    • unit weight, g = 18.9 kN/m3 (120 lbs/ft3)
    • cohesion, c = 47.9 kN/m2 (1000 lb/ft2)
    • angle of internal friction, f = 0 degrees
  • Pile Information
    • driven
    • wood
    • closed end



Try a pile depth, D = 2.4 meters (8 feet)
Try pile diameter, B = 0.61 m (2 ft)

Use a factor of safety, F.S = 3. Smaller factors of safety are sometimes used if piles are load tested, or the engineer has sufficient experience with the regional soils.

Determine ultimate end bearing of pile,

Qp = Apqp
Ap = p(B/2)2 = p(0.61m/2)2 = 0.292 m2                                      metric
Ap = p(B/2)2 = p(2ft/2)2 = 3.14 ft2                                                        standard
qp = 9c = 9(47.9 kN/m2) = 431.1 kN/m2                                     metric
qp = 9c = 9(1000 lb/ft2) = 9000 lb/ft2                                           standard
Qp = Apqp = (0.292 m2)(431.1 kN/m2) = 125.9 kN                    metric
Qp = Apqp = (3.14 ft2)(9000 lb/ft2) = 28,260 lb                           standard


Determine ultimate friction capacity of pile,

Qf = pSqfL

p = 2p(0.61m/2) = 1.92 m                                                            metric
p = 2p(2 ft/2) = 6.28 ft                                                                 standard


upper 1.5 m (5 ft) of soil

qfL = [ks tan d]L = [kgD tan d]L

k = 1.5; lateral earth pressure coefficient for piles, value chosen from Broms low density timber
g = 19.6 kN/m3 (125 lb/ft3); given effective soil unit weight. If water table, then g – gw
D = L = 1.5 m (5 ft); segment of pile within this soil strata. Check to see if D < Dc
Dc = 15B = 9.2 m (30 ft); critical depth for medium dense sands. This assumption is conservative, because the soil is gravelly, and this much soil unit weight for a sand would indicate dense soils. If D > Dc, then use Dc
d = f(2/3) = 20 deg; external friction angle, equation chosen from Broms timber piles
B = 0.61 m (2 ft); selected pile diameter
f = 30 deg; given soil angle of internal friction

qfL = [1.5(19.6 kN/m3)(1.5m)tan (20)]1.5 m = 24.1 kN/m            metric
qfL = [1.5(125 lb/ft3)(5ft)tan (20)]5 ft = 1706 lb/ft                         standard


soils below 1.5 m (5 ft) of subgrade

qfL = aSu

Suc = 2c = 95.8 kN/m2 (2000 lb/ft2); unconfined compressive strength
c = 47.9 kN/m2 (1000 lb/ft2); cohesion from soil testing (given)
a =    1    [0.9 + 0.3(Suc – 1)] = 0.3; because Suc > 48 kN/m2, (1 ksf)
L = 0.91 m (3 ft); segment of pile within this soil strata

qfL = [0.3(95.8 kN/m2)]0.91 m = 26.2 kN/m                                metric
qfL = [0.3(2000 lb/ft2)]3 ft = 1800 lb/ft                                         standard


ultimate friction capacity of combined soil layers

Qf = pSqfL

Qf = 1.92 m(24.1 kN/m + 26.2 kN/m) = 96.6 kN                         metric
Qf = 6.28 ft(1706 lb/ft + 1800 lb/ft) = 22,018 lb                            standard


Determine ultimate pile capacity,

Qult = Qp + Qf

Qult = 125.9 kN + 96.6 kN = 222.5 kN                                       metric
Qult = 28,260 lb + 22,018 lb = 50,278 lb                                      standard


Solve for allowable bearing capacity,

Qa =  Qult     

Qa   222.5 kN    = 74.2 kN;  Qa > applied load (66.7 kN)     o.k.     metric
Qa   50,275 lbs    = 16,758 lbs  Qa > applied load (15 kips)   o.k.     standard



Wood pile shall be driven 8 feet below the ground surface. Many engineers neglect the skin friction within the upper 1 to 5 feet of subgrade due to seasonal variations or soil disturbance. Seasonal variations may include freeze/ thaw or effects from water. Notice how the soil properties within the pile tip location is used in the end bearing calculations. End bearing should also consider the soil layer(s) directly beneath this layer. Engineering judgment or a change in design is warranted if subsequent soil layers are weaker than the soils within the vicinity of the pile tip. Typical methods for increasing the pile capacity are increasing the pile diameter or increasing the embedment depth of the pile.


The position of ground water has a significant effect on the bearing capacity of soil. Presence of water table at a depth less than the width of the foundation from the foundation bottom will reduce the bearing capacity of the soil.

The bearing capacity equation incorporating the ground water table correction factors is given below.


Where clip_image004 = Ultimate bearing capacity of soil in clip_image006

c = Cohesion of soil in clip_image006[1]

Nc, Nq, N? are Therzaghi’s bearing capacity constants.

clip_image008= depth of foundation in meters

B = Width of the foundation in meters

clip_image010 and clip_image012 are water table correction factors

The water table correction factors can be obtained from the equations given below.

1. When the water table is below the base of foundation at a distance ‘b’ the correction clip_image012[1] is given by the following equation


when b =0, clip_image012[2] = 0.5

2. When water table further rises above base of foundation, correction factor clip_image010[1]comes in to action, which is given by the following equation.


when a =clip_image008[1], clip_image010[2] = 0.5


Fig 1: Showing the influence of water table below foundation

The use of these equations is explained with the help of the Fig 1.

First let us begin with the correction factor clip_image012[3]

When water table is at a depth greater than or equals to the width of foundation, from the foundation bottom, the correction factor clip_image012[4] is 1. i.e. there is no effect on the safe bearing capacity.

Let us assume water table started rising then the effect of clip_image012[5] comes in to action. The correction factor will be less than 1. When the water table reaches the bottom of foundation, i.e, when b = 0, clip_image012[6] = 0.5.

Now let us assume water table further raises, above the depth of foundation. When the depth of water table is just touching the bottom of foundation, a = 0. This means clip_image010[3]= 1.0. On further rising, when the water table reaches the ground level, Rw1 becomes 0.5.

Hence, the assessment of ground water level is an important aspect in any site investigation.