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What is a building foundation?

Building foundations are one of the most critical elements of any project, even though they aren't visible when the home or structure is complete.

A foundation refers to the lower part of a structure, which is designed to distribute the weight of the new building evenly and provide a firm footing. It is vital that you choose the right type of foundation and concrete - for the soil type and application - as errors could have serious ramifications and even involve a completed project being demolished. Take a look at our guide to concrete types and, if in doubt, always seek advice from an expert such as a building inspector or structural engineer.

Building regulations and foundations

Getting the foundations of your building or extension right first time is vital if you are to have a successful outcome. This applies not just to the type of foundations you use but also to a number of other factors such as distance to boundaries, ground conditions soil type, adjacent structures, trees, drains and sewers.

As with any project, get the advice and support of experts early on to ensure your project meets all of the relevant regulations and you don't have any nasty shocks further down the line.

Types of foundations in building construction

It is worth carrying out a soil survey before you decide which type of building foundation you require as ground conditions have an important part to play. This is usually done by digging holes at various points across the site and using the results to assume the conditions throughout.

Foundations are generally broken into two categories: shallow and deep. Shallow foundations are the most common type used for small buildings and domestic projects. The depth of these is generally less than their width and they are commonly used for house extension foundations.

Taller commercial or residential buildings, or those built on very weak ground, will require deep foundations, which carry the load of the structure through the weak soil to the stronger soil or rock below. We offer concretes suitable for all types of foundations.

Shallow foundation types

Individual footing or isolated footing

Also known as a spread footing or pad foundation, this type of foundation is used to support a single column and is square, rectangular or circular in shape. They are a uniform thickness and are designed to carry and spread concentrated loads. The size is calculated on the load and ground conditions.

Combined footing

These concrete footings are usually rectangular in shape and support two or more columns which are so close to each other their individual footings would overlap.

Strip foundation

A strip footing is used for load-bearing walls including footings for extensions and conservatories and house foundations. They are also used to accommodate a row of closely-spaced columns. The wider base of this foundation type spreads the weight over a wider area and provides better stability.

Raft or mat foundation

A raft or mat foundation is a large slab supporting a number of columns and walls. This type of foundation is spread across the entire area of a building and is used when soil pressure is low or where columns and walls are so close that individual footings would not be appropriate or cost effective.

Deep foundation types

Pile foundations

Pile foundations are used when ground conditions near the surface are not suitable for heavy loads. Piles are driven into the ground using specialist equipment and filled with concrete before a ground beam is added to provide a surface to build on.

Drilled shafts or caissons

Drilled shafts, also known as caissons, are foundations that are cast in-situ. A column is drilled to the required depth before reinforcing steel is lowered into the hole and then filled with concrete.

Building foundations: a step-by-step guide to creating concrete footings

Your finished structure will only ever be as good as the foundations it is built on so, if you are in any doubt about which type of foundations to use, get expert advice from a building inspector or structural engineer. Once you have decided, make sure you get your concrete footings right by following our step-by-step guide:

Prepare the ground

It doesn't matter how big or small your concrete pour is, the first step - once all relevant permissions are in place - is to prepare the ground. Use wooden pegs and string to mark out the area where the concrete is going to be poured, allowing an extra 75mm to accommodate the formwork, which will hold the wet concrete in place when it is drying.

Then dig your foundations to the required depth: for strip footings this is generally to undisturbed, solid ground, while for individual footings and floor slabs you will need to allow enough depth for your sub base (100mm) and damp-proof membrane (dpm) as well as the concrete itself. This is much quicker and easier with a small mechanical excavator - providing access allows. Make sure all debris, stones and plant material are removed before levelling and compacting the soil to create a level base.

Next add your sub base and compact again. For most domestic concrete footings, such as extension foundations, 100mm of base aggregates is adequate. Then lay a dpm, ensuring the edges are turned up to form a tray and any joints are overlapped and taped. This will protect the underside of the concrete from rising damp and any chemicals ground water might bring in contact with the concrete as well as helping to prevent it drying out too quickly, due to water being drawn into the sub base, which will improve the final strength and reduce the chance of it cracking.

The next step is to build your formwork, which is usually made from well-supported 25mm thick timber planks, to keep the concrete in place until it has had a chance to set. The formwork needs to be as deep as the concrete slab will be.

It is vital that you then use a laser or spirit level to check the formwork is even as this determines the finished level of concrete.

Ordering your concrete

Once the site is prepared, you are ready to lay your concrete. As well as the type of foundation, it is also important to know which type of concrete to use. Soils which contain sulphates, for example, can attack concrete over time and cause an expansive reaction. This can be overcome by using design chemical classes (DC), which help provide long term durability. If you are unsure, take a look at our guidance and/or seek advice from a structural engineer.

You may also find using a concrete calculator useful in deciding how much concrete to order. It will ask for the basic shape of the area - square/rectangle, right-angled triangle, parts of a circle - and dimensions (length, width and depth) to provide you with an estimate of the volume you need. If you've got a complicated area to estimate you can build up the calculations by adding different shapes together. The depth of concrete you need will depend on the use: footings for extensions, for example, will need to be at least 200mm thick, while around 100mm should be deep enough for a shed base.

You also need to consider if you need to order a concrete pump. Using a pump is perfect when you are dealing with large volumes of concrete or when time is tight and you don't have the manpower to use wheelbarrows (you can pump approx. 1m3 of concrete per minute). You will also need to use a pump if the concrete mixer truck can't get close enough to the pour area or access to your site is restricted, underground, within an existing building or at height.

Pouring the concrete

Time is not on your side as concrete typically starts to go off within two hours of being mixed. The actual time will depend on the type of concrete and the ambient temperature: in cold weather it can take twice as long for the concrete to set; in hot weather the setting time could be reduced to 30 mins.

As a result, the concrete will need to be unloaded and levelled as quickly as possible, so make sure you have all the tools you will need at hand including a rake/shovel to move the concrete around and roughly level it and a straight-edged piece of timber to tamp down the concrete and eliminate any air pockets. The concrete is usually wet enough that it can be pulled around the trench using rakes,(we would suggest an S4 consistence for trench filling) before the surface is levelled out and tamped down to remove any trapped air. This is most efficiently achieved using a suitably sized vibrating poker. When the surface has been compacted to the marked-out level it can be smoothed and levelled with a conventional hand float.

It's important to make sure there's enough room on site for the delivery truck: they are around 9.5 metres long, three metres wide and four metres high with a turning circle of about 17.5 metres and weigh up to 32 tonnes. Ready-mixed concrete trucks have extension ramps that can reach around three or four metres so unless the concrete can be off loaded at various positions around the site, you may need to use a concrete pump.

If you are using wheelbarrows, make sure you have the manpower available to speed up the job as 1m3 of concrete will fill around 30-40 wheelbarrows! Paths to the pour must be cleared and planks laid to deal with any slopes or uneven ground.

It is not advisable to lay concrete in any adverse weather conditions but, if it is unavoidable, there are a few things to consider. The minimum air temperature to pour concrete is 3°C to make sure that ice doesn't form within the mix, which could compromise the strength of the concrete. You should also never pour on top of ice or frost so, if this is looking likely, protect the sub base with insulating blankets or thaw it with heaters before the pour, or ask about our Fast track concrete range.

You can pour concrete in the rain as long as the ground drains well and there aren't any rainwater pools. Once it is poured, cover using tarpaulin or sheeting while it cures. Heavy rain will damage the surface of the concrete so, if appearance is important, make sure there is cover to keep the rain away until you are ready to apply the final finish.

The concrete will be reasonably wet when it is poured so a shovel or rake can be used to roughly level the concrete. A straight-edged piece of timber can then be used to tamp down the concrete, eliminating any air pockets. Repeated tamping will create a reasonably smooth surface but a steel float trowel can be used as the concrete starts to harden for a finer finish. It is worth noting that smooth concrete can be quite slippery so often a 'rough' tamped or brush finish is preferable.

Curing your concrete

It is important that the concrete doesn't dry out too quickly as it hardens as this can cause a weak/dusty surface. The easiest way to achieve this is to keep the slab damp by covering it with plastic sheeting, making sure the edges are sealed to prevent wind tunnelling effects. This is particularly important in temperatures over 20°C or if there is a stiff breeze that could dry the surface. Also, if temperatures are likely to dip below 4°C, a frost blanket or similar should be used to insulate the slab and protect the surface from frost. More information on cold weather concrete can be found here.

Follow-on work should be possible within 48 hours, although it is worth checking with your concrete supplier, and it is best to leave any formwork for 72 hours to avoid any possible damage to the edges of the concrete. The building inspector may also insist on examining the concrete foundations before any bricks or blocks are laid, so make sure you have checked before you start the next phase. Concrete takes 28 days to reach its full strength.

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What is a building foundation?Building foundations are one of the most critical elements of any project, even though they aren't visible when the home or structure is complete.A foundation refers to the lower part of a structure, which is designed to distribute the weight of the new building evenly and provide a firm footing.

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Dig deep into the different types of house foundations by looking into the options and materials availabe as well as other considerations in order to build a solid foundation for your home.
When building a home from the ground up, considering the main structure and systems would come up as one of the first decisions to make. It also stands as one of the critical factors to consider. House foundations come in different types and various techniques so learn all about them in order to find the right type for your home design.

Related: Types of Decorative Concrete | Types of Concrete Cleaners | Types of Concrete Saws | Concrete Alternatives | Cinder Block Dimensions

I. House Foundation Guide

You have many decisions to make before construction begins on your new home. Deciding on the type of foundation may be the most important-so knowing what options and materials are available is essential.

The average weight of a house is over 200 tons-including your belongings-so a strong foundation is crucial if you want a home that will last.

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A. House Foundation Types

There are three main foundation types; basement, crawlspace, and concrete slab. A fourth, but a less common option, is wood foundations.

1. Basement Foundation (Two Types)

Full Basement

Basement foundations have structural walls extending underground. Two types are common: full and daylight. A full basement is entirely underground, either with no windows or small ones at ground level.

Basement foundations can be finished (see finished basement ideas here and see the different types of finished basements here) or unfinished. Unfinished basements often serve as storage areas or house water heaters, furnaces, and other household equipment.

Daylight Basement

A daylight basement is on a slope. Some walls are below ground, blocking daylight, and others are partly or entirely above-ground.

Achieving a daylight or walkout basement requires the right slope on your lot. But if you don't mind spending a lot of money on prepping your home build site, it is possible to grade the lot to accommodate a daylight basement.

Basement foundations require either concrete masonry units (CMUs) or concrete walls (poured concrete). Basement foundations are the most expensive option, but they also let you extend your living space if you decide on a finished basement.

2. Crawlspace Foundation

A crawlspace foundation involves short foundation walls on footings. These types of foundations are usually unheated but have ventilation to avoid moisture buildup. They use poured concrete or mortared concrete blocks, and they're less expensive than a full basement.

Many people consider a partial basement to be a crawl space since you can store some items there but can't convert it into a living space.

3. Concrete Slab Foundation

Concrete slab foundations, or slab-on-grade foundations, are a common option in many areas. They're best for climates where the ground doesn't freeze and thaw throughout the winter. These types of house foundations help protect against termites.

Accessing water and drainage pipes can be complicated, however, because those features typically lie underneath a few inches of concrete. Slab-on-grade foundations are one of the least expensive foundation options.

4. Wood Foundation

Wood foundations are often standard in northern areas. They can have a crawl space underneath, too. It's also common to find basements that layer pressure-treated wood on top of concrete floors-but technically, such a combination would count as a concrete foundation.

B. Foundation Materials and Methods

Though foundations are often cement or wood, there are variations. Here are common materials you can find for foundations.

1. Poured Concrete

Poured concrete walls are dense, resisting breakage and cracking. Many builders prefer them over concrete blocks because they don't allow water or earth in since they're a solid piece.

2. Precast Concrete Panel

Instead of pouring concrete on-site, some builders opt for precast panels instead. Precast concrete panels move into place via crane, and they can be challenging to work with. However, they can save time since you don't have to wait for the concrete to cure while placing your walls.

3. Concrete Masonry Units

Concrete masonry units or CMUs are heavy-duty building blocks for creating basements. Installing the blocks requires leveling and jointing the pieces together. Waterproofing is also crucial to avoid water seeping in.

4. Stone

Stone basements are no longer common, but you might find them in older houses. These types of house foundations use a mixture of stones and a mixture of cement to form a solid barrier. They can crack and chip, so most builders shy away from such materials in modern homes.

Of course, nothing is stopping you from adding a stone façade to your basement or foundation.

5. Wood

Since about 1960, pressure-treated lumber has been a common foundation material. Wood foundations are cheap, easy to assemble, and can resist moisture and insects. However, wood doesn't last forever, so it's gradually become less popular as a foundation-building material.

C. Foundation Construction Methods

You can build a foundation in a few different ways. Here are some other standard construction methods.

1. Footing and Stem Wall

A stem wall foundation is common in areas with low to moderate frost because they are very stable. The multi-step process involves pouring a footer, then laying blocks to form a wall to the finished slab height.

Footing and stem walls take a while to complete, but the result is a solid foundation that is resistant to issues like water and ground movement.

2. Pier and Beam

Pier and beam foundations are more common in commercial and industrial applications. However, for larger residential homes, many builders will use drilled shaft concrete piers and beams.

A pier and beam foundation is ideal where the soil is clay and has high plasticity. But you'll also need a structural engineer to oversee the project since the design and soil analysis are vital factors for a safe and robust build.

3. Pier and Beam for Manufactured Homes

For manufactured home installations, a different type of pier and beam foundation is useful (and often affordable). First, anchors go into the ground to hold against wind and other weather. Straps attach to your home's steel frame to hold it in place. Then, outriggers and cross-members go on to add extra weather resistance.

The base can be steel, but you can also opt for concrete or ABS plastic pads underneath. Installation can be quicker with this foundation, but it's only applicable to manufactured or mobile homes.

4. Slab on Grade/Monolithic Slab

When construction workers pour a slab on grade-AKA, a monolithic slab -they complete the pour in one go. The footing, stem wall, and concrete subfloor all go down at the same time, and the slab is a few inches thick. Instead of footers, there are thicker areas of concrete where load-bearing walls go.

Slabs contain either rebar or cables for strength, and they can handle homes, garages, sheds, and more.

5. Pre-Poured Slab

Pre-poured slabs are precast foundation panels that move into place with the help of a crane or other heavy equipment. They can make a foundation installation much faster, but they're also more expensive than pouring a concrete slab

II. More Details

Here are the factors that affect foundations, plus pricing and build considerations.

A. Climate Required

Some house foundation types aren't suitable for specific climates. For example, environments that experience extreme temperatures aren't ideal for slab foundations. As the water freezes and thaws, the concrete can crack from the pressure. In contrast, warmer climates may not benefit from wood foundations since termites can pose a threat.

Climate is a crucial influence over your build plans, so don't get too attached to a particular foundation type until you see what will work where you live.

B. Lot Grade and Soil Type

You might be fortunate enough to live in an area with a mild climate, but that doesn't mean you can choose any foundation. The grade of your lot and where you decide to put your home can affect the compatibility of certain house foundation types.

The soil can also affect the foundation construction. If there is rock below your build site, for example, you might need a structural engineer to examine the lot and figure out a plan for building over it. In other cases, unstable soil could mean you need to select a different build site.

Lot grading can also impact your ability to have a specific foundation build. You might want a daylight basement, but if the lot isn't graded just so-or if you don't have modifications in your budget-you might only be able to choose a traditional basement.

C. Utilities and Accessibility

With some types of house foundations, it's easy to get in and fix things when they break. For example, you might need to enter a crawlspace to service your home's plumbing. But in a poured concrete foundation, for example, the pipes might lie under inches of concrete.

How accessible your home's internal structures depend on the type of foundation and the layout of the features underneath or inside it.

D. Home Style and Design

The architecture or overall design of your home may dictate the type of foundation you need. Or, you might be installing a mobile home over the foundation you choose. While you can place a manufactured home on almost any foundation, many homeowners opt for pier and beam foundations unique to manufactured homes.

Of course, you can choose whatever foundation you prefer, but costs-and engineering issues-can creep up, too.

E. Cost and Pricing

The cost of your foundation depends on many factors, including the average cost of labor in your area. Here are the deciding factors when it comes to foundation pricing.

1. Square Footage

The lower the square footage of your home, the cheaper your foundation may be. You can expect to spend anywhere from $4 to $7 per square foot on a concrete foundation.

At the same time, a single-story home foundation is often more expensive than a multi-story one. It might seem counterintuitive, but the upper floors don't need additional concrete foundations, so going vertical might save you money overall.

Plus, per square foot, it's cheaper to build a two-story house anyway.

2. Construction Type

Of course, the type of foundation you ultimately choose will influence the price more than any other feature. The most expensive foundations are basement builds-especially if you want a finished basement-while the least costly is a concrete slab.

A crawlspace foundation would be mid-range, though you might find pre-made concrete slab solutions that are around the same cost.

3. Foundation Depth

The deeper your contractor must dig, the more expensive the foundation project will be. But in many climates, you will need to have a deep foundation-below the frost line-to protect your home and its structural integrity.

4. Other Pricing Considerations

A foundation is a foundation, right? Not exactly. Pricing also depends on materials costs, extra features, and transportation costs.

For example, installing radiant heating in the floor, which can save on heating and burst pipe costs, adds a significant bump to the bottom line. If you need additional waterproofing or sealant due to climate or site drainage issues, those can also add up.

5. Average Price of a Home Foundation

A home foundation costs anywhere from $4,000 to $175,000. Pricing varies widely based on the materials, time required, and the foundation type.

For example, a slab basement typically comes in under $21,000, while a basement foundation can cost up to $175,000. Here's an overview of typical foundation project costs based on foundation type.

Slab foundation: $4,500-$21,000

Crawl space foundation: $8,000-$21,000

Basement foundation: $10,000-$175,000

Keep in mind that foundation projects also require permits, which your builder may or may not handle for you.

III. How to Choose a Foundation Type

If you are building from the ground up, you can choose the right foundation type for your home. Here's how.

A. Site Considerations

Depending on your home building site and layout, one type of foundation may work better than another. Here are the natural factors that impact your site.

1. Water Tables

A groundwater table is a boundary between unsaturated and saturated soil. Water tables rise and fall with the seasons, and depending on your lot, they may impact drainage at the building site. Water can even seep out of the ground and affect your foundation.

2. Soil Conditions

Soil conditions -such as the type of soil, different layers, and hardness-also influence the type of foundation that's suitable for your building. More stable ground, for example, means you don't need as robust a foundation as if the soil is soft.

A drilled pier foundation, for example, is ideal for ensuring your home rests on the hard rock rather than in soft surface dirt. The type of backfill you use also influences the stability of your foundation. Most people choose store-bought filler material such as limestone or aggregate to backfill the foundation.

B. Local Climate

Your local climate can also influence what type of foundation is best. Frost, for example, is a significant factor. If you live in an area where the ground frequently freezes and melts, you could see cracks in your home's monolith slab foundation. In that case, a post and pier foundation might be a better solution.

Or, if you live somewhere with a high risk of tropical storms, a foundation that can withstand flooding is preferable. Again, a post and pier option may work better than a full basement or slab. Then again, in more moderate climates, a monolith slab is often sufficient and a budget-friendly choice.

C. Foundation Purpose

The purpose of a mono slab is very different than that of a daylight basement. Knowing what purpose you want your foundation to serve is vital since it affects how you'll use your home.

1. Extra Living Space

If you want to add extra space to your home's floor plan, choosing a basement foundation might be the right fit. A finished basement adds square footage to your house and can function as an extra bedroom, game room, media room, or guest lodging.

Plus, finished basements enhance your home's resale value. Only about 30 percent of family homes built after 2013 have full or partial basements. In comparison, 54 percent are on slabs and 15 percent include a crawl space.

2. Outdoor Living

For optimal outdoor living, choosing a walkout (or daylight) basement might be the way to go. You can include windows, stylish doors, and even a patio on your walkout basement. This way, you can enjoy entertaining in your backyard -or even rent out your basement as an apartment unit.

3. Storage

Obviously, a concrete slab or wood foundation doesn't offer much in the way of storage space. If you want to be able to stow belongings-or appliances like the water heater-below the floor, a foundation with a crawl space is a must.

4. Stability

Most homeowners want stability in their foundations. But for people who live in floodplains, a stable foundation is the top priority when building. Elevated slab foundations are one innovative solution to flood issues.

An elevated slab foundation, like Tella Firma's, combines a slab foundation with a pier-and-beam system. The elevated foundation takes a little longer to build and is more expensive than standard foundations-but it can save you money if water damage is a concern.

The suspended foundation is ideal for clay soils, which expand and contract throughout the seasons, and wetter conditions.

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Dig deep into the different types of house foundations by looking into the options and materials availabe as well as other considerations in order to build a solid foundation for your home. When building a home from the ground up, considering the main structure and systems would come up as one of the first decisions to make.

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Foundation design and performance depend on two factors, the nature of the ground on which they are placed and the load, which in the case of a house isn't huge. For self-builds foundation design is therefore mostly about matching house type to ground type, and this is only a job for a structural engineer.

A site visit will come first, e.g. are the neighbouring houses showing cracks or their rooflines sagged - both may be an indication of subsidence caused by ground movement. (Sagging rooflines could also indicate spreading walls or weakened roof timbers.) Trial holes give more detailed information on the site conditions.

Before any excavation, including trial pits, commences, it's very important that you locate any services running through the site. Your local council may have plans showing their location, as will the telecoms and gas companies. Neighbours may also be able to help. It should never be assumed that the site is free from services.

'Protect open trenches and have the site well signed warning of the dangers, not just the entrance but also around it and on access roads...'

Protect open trenches and have the site well signed warning of the dangers, not just the entrance but also around it and on access roads. All machinery should be properly parked and locked when not in use.

Soil types

Oak trees tend to flourish in heavy soils, conifers in peat, willow and alder in wet loam, beech light clay and lime trees in limestone. Nearby trees, groundwater as well as water streams all need to be examined as they could impact on your foundations.

Sand and gravel soils, which can move or settle during heavy rain or long dry spells, often call on raft foundations. Clay tends to compress gradually and houses built on this type of ground may settle gently over time, with the common solution of strip foundations. Peat is mostly found along the western seaboard and midland areas of Ireland and is unsuitable for building on - options are to dig out and fill (with raft or strip foundations on top) or piled foundations.

Rock is very common in coastal areas and appears sporadically throughout the rest of the country. Whilst this is a good base to build on, rock breaking if required is an expensive process.

STRIP

The most common type of foundations for Irish self-builds. It consists of a strip of concrete laid in a shallow trench, forming a stable base for each wall element. It can be used for both lightweight and heavyweight buildings where the soil is uniformly firm and deep, or for lightweight buildings which have a firm layer over a soft layer. Minimum depth according to NI Building Regulations for example, is 450mm which is required to avoid the adverse effects of frost.

RAFT

This type of foundation spreads the load over a bigger area of ground and is more expensive to form than strip footings because it is a slab of reinforced concrete the size of the house footprint. The slab is deepest immediately under the outer walls, the edge beam, and load bearing internal walls, cross beam. The steel reinforcement for the edge beams and cross beams is often pre-fabricated and lifted into position.

Mostly used in cases where the soil type is uniform across the site and consists of either deep, soft soil or filled soil which is holding water. Where very wide strip foundations would be required, it can sometimes be more economical to use a raft instead.

PILES

These are concrete columns sunk deep into the ground to support the foundations. Specialist contractors drive them into the ground in sections, or they may use steel tubes later filled with concrete as an alternative. Either way the piles are located to an engineered design, and are very common in filled or soft ground. A mini-piling service is normally sufficient for houses with some companies offering a complete subfloor system. 'T' shaped concrete beams support the sub floor slab with the beams in turn being supported by the piles. Concrete is poured between the beams forming a raft-like slab, and the sub-floor is ready for the follow-on trades. The system is engineered to suit the specific house and is ideal for filled ground.

A third system is similar to that above and involves pre-cast concrete planks placed on the beams to form a sub-floor. This is quicker to install but may be more expensive.

PADS AND BEAMS

When piling isn't possible, concrete pads can be poured to support cross beams. They are tied together by steel reinforcing to prevent movement. They are made on site from concrete poured into temporary forms.

ECO-FOUNDATIONS

Rubble trenches we commonly associated with our old stone-walled houses, but it was also popularised by architects such as Frank Lloyd Wright. The construction was usually of a shallow trench, filled with rubble which may or may not have been cemented with a basic mortar such as a clay and lime mix. More sophisticated foundations would use a rubble fill between built stone facings, similar to a dry-stone wall, but in a trench.

Nowadays, these types of foundations are increasingly being used where a light eco-structure is to be built, such as rammed earth walls or strawbale and timber walls. The rubble trenches can also be drained out to a soakaway to improve the site drainage and maintain a dry void under suspended floors. Since the rubble is essentially flexible to some degree, some care must be taken to ensure that either the structure can absorb a bit of movement or that the foundation is suitably compacted and load tested for the avoidance of differential settlement. The technique is generally regarded as unsuitable for bearing on soft or expansive soils.

'For self-builds foundation design is mostly about matching house type to ground type.'

Earthbags, meanwhile, are of particular value in countries where concrete is too expensive to transport to remote areas, but where spare fill material is plentiful. The method involves filling a trench with bags or tubes which are filled with compacted soil. Often, barbed wire is used between layers to help anchor them together. If there is a scarcity of materials for building more
traditional types of walls and roof, the layers can be brought up into a dome shape to form the walls and roof of the structure. The bags are then plastered to keep out the weather. If the soil is not free-draining, the bottom layers can consist of gravel-filled bags and incorporate a drain out to a soakaway.

Padstone is perhaps the simplest and most environmentally-friendly of all foundation types. A similar form of foundation is the staddle-stone (also known by various other names), often similar in appearance to a mushroom - consisting of a domed top stone on top of a columnar one, which were typically used to carry the building above ground to prevent vermin infestation of foodstores. These types of surfacelevel foundation - or variations on the theme, will easily allow structures to be deconstructed at the end of their designed lifetime.

Screw piles are now available for small or light structures; they are removable and re-usable too.

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Foundation design and performance depend on two factors, the nature of the ground on which they are placed and the load, which in the case of a house isn't huge. For self-builds foundation design is therefore mostly about matching house type to ground type, and this is only a job for a structural engineer.

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DIGGING OUT AND CONCRETING THE FOUNDATIONS ON A NEW BUILD BUNGALOW