Footings Guide

This article covers Footings, with practical UK guidance, examples and key points to consider before planning or ordering materials.

Work out concrete volume for UK strip footings, trench-fill foundations and pad foundations — including waste allowance, ready-mix ordering quantity, bag estimates, cost range and 2026 Building Regulations guidance.

How the UK Footings Guide Works

This Footings Guide UK estimates the volume of concrete needed for strip foundations, trench-fill foundations and pad footings by multiplying the measured length, width and depth of the concrete section. It then adds a practical waste allowance for real site conditions. In theory a footing is a simple rectangular prism, but in real UK groundworks the trench can widen during excavation, sides can slump, bottoms can be uneven, and Building Control may ask for deeper or wider excavation before the pour is approved.

The standard volume formula is: concrete volume = length × width × depth . Measurements must be converted to metres before multiplying. For example, a 12m long strip footing that is 600mm wide and 225mm deep is determined as 12 × 0.6 × 0.225 = 1.62m³. With an 8% waste allowance, the practical order quantity becomes about 1.75m³. For ready-mix concrete, it is usually better to round sensibly rather than order the exact mathematical volume, because a small shortage at the end of a footing pour can be expensive and disruptive.

2026 Site Note — Measure the Excavation, Not Just the Drawing

Architectural drawings and structural details give design dimensions, but the actual concrete order should normally be checked against the trench after excavation. A footing specified as 600mm wide can become 650mm or 700mm wide if the sides break away in clay, made ground or wet sand. Always measure at several points and use the worst realistic average before ordering.

Strip Footings

Best for continuous load-bearing walls, house extensions, garages and simple masonry walls where the load is spread along a linear trench.

Pad Foundations

Used below isolated columns, steel posts, timber posts and concentrated loads. Volume is determined per pad, then multiplied by the number of pads.

Ready-Mix Ordering

Order volume includes waste, overdig and practical rounding. For larger pours, ready-mix is usually more reliable than hand mixing dozens of bags.

A key advantage of using a dedicated foundation concrete volume guide is that it helps avoid both under-ordering and over-ordering. Under-ordering leaves cold joints, delays and emergency mini-mix charges. Over-ordering means paying for concrete that may need to be disposed of. Because concrete starts curing as soon as it is batched, accurate ordering is part of good workmanship, not just budgeting.

Strip Footing Guide UK — Typical Dimensions & Use Cases

A strip footing is a continuous concrete foundation placed below a load-bearing wall. In domestic construction it is common under external walls, cavity walls, single-storey extensions, garages, conservatory replacements, garden rooms with masonry walls, and some internal load-bearing walls. Strip foundations spread the wall load onto the ground over a wider area. They are simple, economical and well understood by UK builders, but they are only suitable where the ground is strong and predictable enough for shallow foundations.

For small domestic projects, a typical strip footing might be 450mm to 750mm wide and 150mm to 300mm deep, but these figures are only broad examples. The correct width and depth depend on wall thickness, loads, ground bearing capacity, nearby trees, frost depth, drains, sloping sites and local Building Control requirements. A two-storey extension, a heavy roof, a retaining wall or poor ground can require much larger dimensions or a different foundation type entirely.

Do Not Treat Generic Widths as Structural Design

this guide estimates concrete volume only. It does not decide whether a footing is structurally adequate. Foundation size must follow Building Control guidance, engineer working, soil bearing capacity and any warranty provider requirements. Approved Document A covers structural elements including foundations, while local inspectors may require deeper excavation if the exposed ground is unsuitable.

• Footing Use: Small garden wall; Typical Width Range: 300–450mm; Typical Concrete Depth: 150–225mm; Common Notes: Depends on wall height and ground
• Footing Use: Single-storey extension; Typical Width Range: 600–750mm; Typical Concrete Depth: 225–300mm; Common Notes: Building Control inspection required
• Footing Use: Two-storey extension; Typical Width Range: 750mm+; Typical Concrete Depth: 300mm+; Common Notes: Often engineer checked
• Footing Use: Garage / masonry outbuilding; Typical Width Range: 450–600mm; Typical Concrete Depth: 150–225mm; Common Notes: Depends on wall and roof load
• Footing Use: Retaining wall footing; Typical Width Range: Engineer specified; Typical Concrete Depth: Engineer specified; Common Notes: Do not guess dimensions

Worked Example: Strip Foundation Concrete Volume

Assume a rear extension has a U-shaped trench with two side returns and one rear wall. The combined length is 18m. Building Control has accepted a 600mm wide trench and a 225mm concrete thickness. The working is 18 × 0.6 × 0.225 = 2.43m³. Add 8% waste: 2.43 × 1.08 = 2.62m³. A practical ready-mix order might be 2.7m³, especially if the trench is uneven or if there are local overdig areas around corners.

Pad Foundation Guide UK — Concrete Volume for Columns & Posts

A pad foundation is an isolated concrete block that supports a concentrated load, such as a steel column, timber post, canopy support, porch post, beam bearing, small frame structure or commercial column. Pad foundations are determined by multiplying pad length, pad width and pad depth, then multiplying by the number of pads. the working method uses the same length field for each pad length, the width field for pad width, the depth field for pad depth and the number field for quantity.

Pad foundations are often more sensitive to design assumptions than strip footings because loads are concentrated. A post or column can impose a high vertical load and may also create uplift, sliding or overturning forces. For that reason, pad foundations for steelwork, retaining structures, commercial projects or large timber frames should be designed by a structural engineer. The concrete volume may be easy to work out, but the safe pad size, reinforcement, bearing pressure and holding-down bolts require structural judgement.

Steel Columns

Steel columns usually need engineered pad sizes, base plates, bolt cages, reinforcement details and concrete strength class to suit the load path.

Timber Posts

Decking, pergola and canopy posts may use small pads, but uplift, post base corrosion and ground moisture should still be considered.

Concentrated Loads

Heavy point loads need checked bearing pressure. A small pad on weak soil can settle even if the concrete quantity is correctly determined.

Pad Volume Formula

Pad concrete volume = pad length × pad width × pad depth × number of pads. For example, four pads measuring 900mm × 900mm × 450mm use 0.9 × 0.9 × 0.45 × 4 = 1.46m³ before waste.

For reinforced pads, remember that the working method gives the gross concrete volume. It does not subtract the small volume of reinforcement, bolts or sleeves, because on site this is normally insignificant compared with excavation tolerance. The bigger issue is whether the pad excavation is the right size, level, clean, inspected and free of standing water before pouring.

Foundation Concrete Specification UK 2026 — GEN, ST, FND & Designed Mixes

Choosing the right concrete for footings is just as important as working out the right volume. In the UK, ready-mix concrete is commonly specified using GEN, ST, FND, RC or designed concrete terminology depending on project type, exposure and structural requirements. For simple domestic strip footings, suppliers may recommend a general foundation mix such as GEN1, GEN3 or ST2, but the correct specification should always come from the approved plans, structural engineer, Building Control officer or ready-mix supplier after considering site conditions.

The 2026 specification context is shaped by BS EN 206 and the complementary UK standard BS 8500 . BS 8500 provides UK-specific guidance for concrete specification, exposure classes, constituent materials and durability. The 2023 update broadened options for lower-carbon concretes, which is increasingly relevant for housebuilders, commercial projects and clients trying to reduce embodied carbon without compromising durability.

Link Concrete Grade to Ground Conditions

Foundation concrete in normal ground is not the same as concrete in aggressive sulphate-bearing soil, contaminated ground or waterlogged excavations. If a site investigation identifies sulphates, acid ground or high groundwater risk, the foundation mix may need an FND designation or designed concrete with a specified DC class.

• Concrete Type: GEN1 / C10-C15 type; Typical Use: Blinding, light non-structural work; Specifier: Builder / supplier guidance; Important Note: Not for every footing
• Concrete Type: GEN3 / ST2 type; Typical Use: Many domestic strip footings; Specifier: Plans, inspector or supplier; Important Note: Common foundation option
• Concrete Type: FND concrete; Typical Use: Foundations in aggressive ground; Specifier: Engineer / site investigation; Important Note: Check sulphate class
• Concrete Type: RC / designed concrete; Typical Use: Reinforced pads, beams, engineered works; Specifier: Structural engineer; Important Note: Do not substitute
• Concrete Type: Lower-carbon concrete; Typical Use: Projects targeting embodied carbon reduction; Specifier: Engineer / supplier / client; Important Note: Check strength gain time

How Much Concrete Should You Order?

For small strip footings under around 1m³, some DIY builders consider bagged concrete or on-site mixing. However, once the volume rises above 1.5m³ to 2m³, ready-mix or volumetric concrete often becomes more practical because foundations should ideally be poured continuously. A 25kg bag of dry concrete typically yields roughly 0.01m³ to 0.012m³ after mixing, so even a 2m³ footing can require more than 160 bags. The labour, consistency risk and mixer time quickly become significant.

UK Building Regulations for Footings & Foundations 2026

Footings are not just a quantity-surveying exercise. They are part of the building’s structural support system, so they normally fall under Building Regulations. Approved Document A gives guidance on structural loading and structural elements including foundations, walls, floors, roofs and chimneys. Approved Document C is also relevant because it covers site preparation, unsuitable material, contaminants, moisture and sub-soil drainage. Together, these documents explain why ground conditions matter before any concrete is poured.

For most house extensions, new houses, structural alterations, garages attached to dwellings and significant masonry outbuildings, the foundation trench must be inspected before concrete is placed. The inspector checks whether the trench reaches suitable bearing strata, whether soft spots have been removed, whether drains or services are affected, whether trees are close enough to influence clay movement, and whether the proposed foundation dimensions match the plans or site conditions.

Never Pour Before Inspection Where Building Control Applies

If you pour foundations before the required inspection, Building Control may ask for evidence, additional investigation or remedial work. In the worst case, concrete may need to be broken out. Always book the foundation inspection once excavation is ready and before ordering the concrete truck.

Trees & Clay

Shrinkable clay near trees can require deeper foundations, heave protection or specialist design. NHBC Chapter 4.2 is widely used for warranty-backed new homes.

Water & Drainage

Standing water, poor drainage or waterlogged trenches can affect concrete quality and bearing ground. Sub-soil drainage may be needed in some conditions.

Contaminated Ground

Made ground, fill, sulphates, radon or methane risk can affect excavation, foundation design, concrete specification and protective measures.

2026 NHBC Standards and Tree-Related Foundation Depth

NHBC Standards 2026 apply to NHBC-registered homes whose foundations are begun on or after 1 January 2026. For tree-related movement, NHBC Chapter 4.2 remains an important reference because it deals with building near trees, hedgerows and shrubs, particularly on shrinkable soils. The required foundation depth can change dramatically depending on tree species, mature height, water demand, distance from the foundation, soil volume-change potential and whether trees have been removed. This is why a simple volume guide should never be used as a substitute for foundation depth design near trees.

If your project is close to existing or recently removed trees, the working method’s concrete volume is only the final arithmetic step. First you need the correct foundation depth and width. The difference between a 900mm-deep trench and a 2,000mm-deep trench can multiply the concrete volume several times if trench-fill foundations are used. On clay sites, the most expensive mistake is often not the concrete price itself but discovering after excavation that the foundation must go much deeper than expected.

How to Measure Footings Before Ordering Concrete

Accurate measurement is the difference between a smooth foundation pour and a stressful site delay. Start by checking the approved foundation drawing, then measure the excavated trench or pad. For strip foundations, measure the total centre-line or trench-line length, including returns and internal load-bearing walls. Avoid double-counting corners. For pad foundations, measure one pad’s length, width and depth, then multiply by the total number of identical pads. If pads differ in size, work out each group separately and add the results.

• Measure length in metres:Add every continuous trench run, including returns, projections and internal walls.
• Measure width in millimetres:Take several readings because hand-dug trenches rarely stay perfectly uniform.
• Measure concrete depth:Use the actual depth of concrete to be poured, not necessarily the full excavation depth if there is blinding or step changes.
• Check trench bottom:Remove loose spoil, mud, roots, organic matter and standing water before inspection and pouring.
• Allow for overbreak:Clay, sandy ground and made ground often increase real volume compared with the drawing.
• Round ordering quantity:Ready-mix suppliers usually work in 0.1m³ increments; mini-mix and volumetric suppliers may have different minimums.

Practical Ordering Rule

For most domestic footing pours, use the determined volume plus 5–10% waste and round up to the nearest 0.1m³. For highly irregular trenches, collapsed sides, steps or difficult access, use 10–15% and discuss the order with your concrete supplier before the truck is batched.

When using a concrete pump, also allow for line priming, pump waste and washout management. Pump waste is not always included in simple footing guides, and the amount depends on pump type, hose length and site setup. For a small domestic footing, pump waste can be noticeable compared with the total volume. Ask the pump operator and concrete supplier how they want the order handled.

Footing Concrete Cost UK 2026 — Ready-Mix, Pumping & Small Load Charges

The concrete volume result is only one part of a realistic footings budget. In 2026, UK footing concrete cost is affected by the ready-mix rate per cubic metre, delivery distance, minimum load size, part-load charges, waiting time, pump hire, weekend delivery, access restrictions and whether a volumetric lorry or drum mixer is used. A straightforward domestic strip footing pour may be priced mostly by cubic metres, while a small awkward job can have a higher effective cost per cubic metre because the delivery and setup costs are spread over a very small volume.

For budgeting, many domestic users enter a ready-mix rate between £120 and £180 per m³, but this should only be treated as an editable estimate. Specialist mixes, FND concrete, fibre reinforcement, rapid-setting mixes, out-of-hours delivery, restricted access and remote rural locations can all increase the final price. London, the South East and congested urban sites can also cost more because of labour, haulage, plant, parking and waiting-time risk.

• Supply Method: Bagged concrete; Typical Best Use: Small post pads, tiny repairs, isolated DIY work; Budget Impact: Higher cost per m³ but no truck delivery; Key Warning: Consistency and labour risk
• Supply Method: Mini-mix concrete; Typical Best Use: Small domestic foundations and tight sites; Budget Impact: Good for 1–4m³ where full lorry is excessive; Key Warning: Ask about minimum load
• Supply Method: Volumetric concrete; Typical Best Use: Jobs where final quantity is uncertain; Budget Impact: Can reduce waste because mixing happens on site; Key Warning: Confirm mix compliance
• Supply Method: Ready-mix drum lorry; Typical Best Use: Larger strip foundations and new-build plots; Budget Impact: Efficient for continuous pours; Key Warning: Part-load and waiting fees
• Supply Method: Concrete pump; Typical Best Use: Rear extensions, long hose runs, poor access; Budget Impact: Adds setup and pump hire cost; Key Warning: Allow line waste

When comparing concrete quotes, ask whether prices include VAT, delivery, part-load charges, waiting time, environmental charges, pump hire, barrowing time and out-of-hours delivery. A supplier that looks cheaper per cubic metre can become more expensive once small-load fees are added. Also confirm whether the supplier can provide the mix designation required by Building Control or your engineer. Saving a small amount on concrete is never worth using the wrong specification in a structural foundation.

Common Footing Working Mistakes to Avoid

Most footing volume errors happen because the working is based on neat drawing dimensions rather than the excavated trench. Real trenches are rarely perfect rectangles. Corners get enlarged, sides collapse, bottoms step down, tree roots require trimming, drains need bridging, and inspectors sometimes ask for additional excavation. A careful builder checks dimensions after digging, not only before digging.

• Using millimetres as metres:A 600mm width must be entered as 0.6m in a manual formula. This guide converts millimetres automatically, but spreadsheet users often make this mistake.
• Forgetting returns:Extension footings often include side returns, internal walls, piers and short returns around corners. Missing a 2m return can under-order concrete noticeably.
• Double-counting corners:Measuring every wall face separately can count corner overlaps twice. Use trench length consistently and check against the setting-out plan.
• Ignoring trench-fill depth:A trench-fill foundation may use the full excavated depth as concrete, not just a 225mm strip. This can multiply the order volume dramatically.
• No allowance for overdig:A mathematically exact order is risky because concrete trenches are rough and ground conditions change.
• Ordering before inspection:If Building Control asks for more depth or width, your order quantity may be wrong.
• Ignoring pump waste:Pump line priming and washout can add practical volume on small jobs.

Watch Out for Drains and Services

Foundations near drains, manholes, service trenches and existing structures may need bridging, lintels, sleeves or special detailing. Do not simply pour concrete around services. Ask Building Control, the drainage contractor or structural engineer before pouring where a footing crosses or runs close to a pipe.

A good site routine is to work out the volume twice: first from the drawings for early budgeting, then again after excavation for ordering. Take photos of trenches, record dimensions, keep the inspection record and save the concrete delivery ticket. These records can be helpful for Building Control sign-off, warranty queries, future property sales and any later investigation.

Stepped Footings, Sloping Sites & Uneven Ground

Sloping UK sites often need stepped foundations rather than a single level strip. A stepped footing changes level in controlled steps so the masonry above can remain properly bonded and supported. The volume working for a stepped foundation is best handled by splitting the footing into sections. Work out each section length × width × depth separately, add the results together, then apply waste. the working method can still be used by entering the combined equivalent length for sections of the same width and depth, but different step depths should be determined as separate groups.

Stepped foundations require careful setting out because the step height, overlap, bearing and masonry coursing must work together. If steps are too abrupt or poorly aligned, they can create weak points, awkward blockwork and inspection problems. On steeper slopes, retaining walls, reinforced ground beams, raft foundations or piled foundations may be more appropriate than standard strip footings.

Sloping Ground

Split the trench into level sections and work out each volume separately. Do not average large step changes where bearing conditions differ.

Masonry Coursing

Steps should suit block and brick coursing so walls above can be built cleanly without weak or awkward transitions.

Inspection Records

Photograph each step before pouring and keep the inspection approval, especially where foundations are later covered by ground floor construction.

If the site has a significant slope, nearby retaining walls or evidence of previous fill, do not rely on generic footing sizes. Ground movement, lateral load and differential settlement can become more important than simple vertical bearing. The safest approach is to obtain a site-specific foundation design and then use this guide purely to estimate the concrete quantity from that design.

Footing Volume Is Not the Same as Foundation Design

this guide estimates concrete quantity for budgeting and ordering. It does not replace Building Control approval, structural design checks, soil investigation, NHBC requirements or engineer-specified foundation details. See the FAQ before using the result on site.

Footings Guide UK — Frequently Asked Questions

Common questions about strip footing volume, pad foundation concrete, UK Building Regulations, ready-mix ordering and foundation costs in 2026.

Multiply the total footing length by the trench width and concrete depth, with every measurement in metres. For example, 20m of footing × 0.6m wide × 0.225m deep = 2.7m³. Then add 5–10% for overdig and waste, giving an order of about 2.85m³ to 3.0m³. If the trench is uneven, wet or wider than the drawing, measure the actual excavation before ordering.

A strip footing normally uses a shallower concrete strip at the bottom of the trench, with blockwork built up to ground level. A trench-fill foundation fills most of the trench with concrete, reducing below-ground blockwork and labour but using more concrete. Trench-fill can be faster on domestic sites, but it becomes expensive if the foundation depth increases, especially near trees or in clay ground.

A 25kg bag of dry concrete typically yields roughly 0.01m³ to 0.012m³ after mixing. That means 1m³ may require around 84 to 100 bags depending on the product yield. For anything above about 1.5m³, ready-mix or volumetric concrete is usually more practical because hand mixing becomes slow, inconsistent and labour intensive. Always check the exact yield printed on the bag.

Many simple domestic footings use a general foundation concrete such as GEN3, ST2 or a supplier-recommended foundation mix, but there is no single grade that fits every site. Aggressive ground, sulphates, groundwater, reinforced pads, commercial loads or engineered designs may require FND concrete or a designed mix under BS EN 206 and BS 8500. Use the grade shown on the approved drawing or specified by the engineer, Building Control officer or ready-mix supplier.

For most extensions, new dwellings and regulated building work, yes. Building Control normally needs to inspect foundation excavations before concrete is poured. The inspector checks ground conditions, depth, nearby trees, drains, services and general suitability. Pouring without inspection can cause approval problems, so book the inspection before scheduling the concrete truck.

There is no universal depth. Footings must reach suitable ground and normally be deep enough to avoid frost action, soil movement and organic material. A commonly referenced minimum is around 450mm below ground level, but clay, trees, made ground, drains, sloping sites or poor bearing soil can require much deeper excavation. On shrinkable clay near trees, foundation depth may be governed by NHBC Chapter 4.2 or engineer design rather than a simple rule of thumb.

For a neat, machine-dug or shuttered footing, 5% may be enough. For typical domestic trenches, 8–10% is more realistic. For hand-dug trenches, wet ground, collapsing sides or irregular excavations, 10–15% may be safer. Discuss very small or awkward orders with the supplier because delivery minimums, part-load charges and pump waste can affect the best order quantity.

You can use it to estimate the concrete volume once a retaining wall footing has been designed, but you should not use it to choose the footing size. Retaining walls create lateral earth pressure, sliding risk, overturning risk and drainage requirements. They commonly need structural design, reinforcement details, weep holes or land drainage, and sometimes planning or party wall considerations.

Related UK Concrete & Building Guides

Use these resources alongside the Footings Guide to plan your concrete, groundworks and Building Regulations package.

For additional concrete quantity and estimating resources, you can also visit ConcreteCalcs.com.