Pad, strip, and raft footing design rules for UK construction — BS EN 1997 Eurocode 7 & BS 8004 compliant
A complete 2026 reference covering concrete footings design rules including minimum dimensions, bearing capacity, reinforcement requirements, frost depth, settlement limits, and practical design steps for every common footing type used in UK residential and commercial construction.
Footings transfer structural loads safely from the building into the ground. Getting the design rules right from the outset — depth, width, reinforcement, bearing capacity — prevents settlement, cracking, and structural failure over the building's design life.
A concrete footing (or foundation) is the lowest structural element of a building, transferring loads from columns, walls, or slabs into the bearing stratum below. The footing spreads the load over a sufficient plan area to keep the bearing pressure below the safe bearing capacity of the soil. Footing type, depth, and dimensions are determined by load magnitude, soil type, frost depth, and proximity to adjacent structures or services.
Concrete footing design in the UK is governed by BS EN 1997-1 (Eurocode 7) — Geotechnical Design, complemented by the UK National Annex and the legacy standard BS 8004:2015 (Code of Practice for Earth Retaining Structures and Foundations). For domestic buildings, Approved Document A of the Building Regulations provides prescriptive rules for simple strip footings that bypass full Eurocode 7 calculations where conditions are straightforward.
Eurocode 7 offers three Design Approaches (DA1, DA2, DA3) for verifying geotechnical limit states. The UK National Annex mandates Design Approach 1 (DA1) — using two separate load and resistance factor combinations (DA1-C1 and DA1-C2) and taking the governing result. For most UK residential strip footings on competent ground, the prescriptive approach in Approved Document A provides a simpler, equally valid route without full geotechnical calculation.
Cross-section schematic of the three primary shallow footing types. Actual dimensions depend on applied loads, soil bearing capacity, and depth to competent strata. All footings must bear below the frost depth — minimum 450 mm in the UK.
The selection of footing type is the first and most consequential decision in concrete footings design. Each type suits a specific combination of structural load, soil condition, plan geometry, and budget. The wrong type — for example, strip footings on soft clay where a raft is needed — leads to differential settlement, cracking, and in severe cases, structural instability. The five types below cover the full range encountered in UK residential and commercial construction in 2026.
Isolated square or rectangular base under a single column
A pad footing is an isolated, square or rectangular concrete base supporting a single column or stanchion. The footing spreads the concentrated column load over a sufficient plan area to keep bearing pressure within the safe limit of the soil. Minimum depth is typically 500 mm in the UK. Reinforcement is provided as a bottom mat in both directions to resist bending and punching shear. Pad footings are the most economical solution for lightly loaded columns on good bearing ground.
Continuous footing under loadbearing walls
A strip footing runs continuously beneath a loadbearing wall, distributing the wall load uniformly along its length into the soil. The most common footing type in UK domestic construction — used under brick, blockwork, and timber frame walls. Approved Document A (Building Regulations) provides direct prescriptive width rules based on total load and soil type, removing the need for full Eurocode 7 design on straightforward domestic projects. Minimum width is 450 mm in most cases; minimum depth is 750 mm (or below frost depth, whichever is greater).
Whole-building slab spreading load across entire footprint
A raft foundation is a reinforced concrete slab covering the entire building footprint, distributing all loads over the maximum possible area. Used where individual footings would overlap, where the soil has low bearing capacity, or where differential settlement must be minimised — particularly on filled ground, soft clay, or sites with variable soil conditions. A well-designed raft acts as a rigid or semi-rigid plate, redistributing uneven settlements across the full slab area. Minimum thickness is typically 300 mm for domestic use, 450–600 mm for commercial.
Two or more columns on a single shared base
A combined footing serves two or more columns that are too close together for individual pad footings, or where one column is at a site boundary and an eccentric pad would cause unacceptable differential bearing pressure. The footing is proportioned so that the centroid of the footing plan area coincides with the resultant of the column loads, ensuring uniform bearing pressure beneath the slab. Reinforcement design is more complex — requiring both longitudinal beams and transverse bands to distribute load between columns.
Deep mass concrete in a narrow trench — no formwork
The trench fill method fills a narrow machine-excavated trench with mass (unreinforced) concrete up to near-ground level — typically used in the UK on shrinkable clay subsoils, tree-affected sites, and where the frost-vulnerable zone or active clay layer extends deep. Because the trench is narrow (450–600 mm wide), no formwork is needed and the concrete is cast directly against the earth sides. Depth typically ranges 900–2500 mm depending on clay shrink-swell zone depth, nearby tree species, and seasonal moisture variation.
The following rules apply to all shallow concrete footing types and reflect the requirements of BS EN 1997-1 (Eurocode 7), BS 8004:2015, and the UK Building Regulations Approved Document A. These are the fundamental parameters that must be established and verified for every footing design before construction commences in 2026.
All footings must be founded below the frost depth to prevent heave damage from freezing ground. In the UK, the minimum accepted depth to the underside of a footing is 450 mm below finished ground level — but most engineers specify 600–750 mm as a practical minimum for strip footings and 500–600 mm for pad footings. On shrinkable clay sites, the NHBC Standards and NHBC Chapter 4.2 require considerably greater depths — typically 900–2500 mm — depending on tree species proximity, tree height, and soil plasticity index.
Approved Document A Table 10 gives direct prescriptive minimum widths for domestic strip footings based on total load condition (number of storeys + floor loads) and soil type. For most UK domestic construction on firm subsoil (bearing capacity ≥ 75 kN/m²), the minimum strip footing width is 450 mm for single-storey and 600 mm for two-storey construction. The footing must never be narrower than the wall it supports, and the projection beyond the wall face must be at least equal to the footing depth on each side (the 45° rule).
Where: N = applied column/wall load (kN or kN/m) | Wf = self-weight of footing | A = footing plan area (m²) | q_allow = allowable bearing capacity of soil (kN/m²)
For unreinforced strip footings (mass concrete), the minimum thickness H must satisfy the 45° dispersion rule: H ≥ P (projection beyond wall face on each side). This ensures load spreads at 45° through the concrete depth without inducing tension — mass concrete has negligible tensile capacity. For reinforced pad footings, minimum thickness is typically 300 mm (to accommodate two layers of reinforcement and minimum cover), with practical thicknesses of 400–600 mm for normal column loads. Raft slabs are typically 300 mm minimum for domestic and 450–600 mm for commercial structures.
Foundation concrete must be specified per BS 8500 and BS EN 206 to suit the ground exposure conditions. For most UK domestic foundations in non-aggressive ground, a minimum C25/30 (RC30/B) mix is appropriate — satisfying XC2 exposure class for buried reinforced concrete. On sulfate-bearing sites (XA classes), a sulfate-resisting cement blend (GGBS or SRPC) is required per BRE SD1 classification. Ground investigation results must be reviewed before finalising the concrete specification for any foundation.
The table below provides indicative allowable bearing capacities and typical footing widths for common UK soil and rock types. These are guidance values only — site-specific values from a ground investigation must be used for final design.
| Soil / Rock Type | Allowable Bearing (kN/m²) | Typical Strip Width (2-Storey) | Min. Footing Depth | Notes |
|---|---|---|---|---|
| Hard rock (granite, basalt) | ≥ 10,000 | 300 mm | 300 mm | Practically unlimited capacity |
| Soft rock (chalk, limestone) | 600–3,000 | 300–400 mm | 450 mm | Avoid dissolution zones in chalk |
| Dense gravel / gravel-sand | 200–600 | 450–600 mm | 500 mm | Low settlement risk |
| Compact sand | 100–300 | 600–750 mm | 500 mm | Check liquefaction risk if saturated |
| Stiff / very stiff clay | 75–200 | 600–900 mm | 900 mm (shrinkable) | Trench fill common on shrinkable clay |
| Firm clay | 50–75 | 750–1000 mm | 900 mm+ | Consider raft or piled option |
| Soft clay / silt | 20–50 | Raft or piles required | Variable | High consolidation settlement risk |
| Made ground / fill | Highly variable | Raft or piles required | Through fill to natural | Ground investigation essential |
Reinforcement in concrete footings resists bending, shear, and punching shear induced by the upward bearing pressure acting against the base of the footing. Unlike columns and beams where bending is in the vertical plane, footing reinforcement is predominantly horizontal — placed as a bottom mat near the underside of the slab where tensile stress is greatest. The following rules apply to reinforced pad and raft footings per BS EN 1992-1-1 (Eurocode 2).
For footings cast directly against earth, nominal cover is 75 mm minimum per BS EN 1992-1-1 cl.4.4.1.3. Where a blinding layer (50 mm lean mix concrete) is provided, nominal cover reduces to 40–50 mm (XC2 exposure class). Always use blinding on all footing pours — it keeps reinforcement at the correct level, prevents contamination, and protects the bearing stratum from disturbance during reinforcement fixing.
Practical minimum bar diameter for footing reinforcement is T12 @ 200 mm centres in both directions for a domestic pad footing. For larger commercial footings, T16 or T20 bars at 150–200 mm centres are typical. Maximum bar spacing is the lesser of 3h or 400 mm (where h = slab thickness) per Eurocode 2. Minimum reinforcement area A_s,min = 0.26 × (fctm/fyk) × b × d, but not less than 0.0013 × b × d.
Pad footings must be checked for punching shear around the column perimeter. The critical punching shear perimeter is taken at 2d from the column face per Eurocode 2, where d is the effective depth of the footing. If the footing depth is insufficient to resist punching shear without links, the depth must be increased — adding shear links to a shallow footing is impractical and costly. A minimum effective depth of d ≥ N / (v_Rd,c × u) is the practical check.
The critical section for bending in a pad footing is at the face of the column. The hogging moment per metre width = q × lx² / 2, where lx is the projection from the column face to the footing edge and q is the uniform bearing pressure. Reinforcement must be placed at the bottom of the footing in both directions with sufficient anchorage length beyond the critical section — typically full bond length + 50 mm end cover.
Reinforced columns are connected to footings via starter bars cast into the footing during the pour, projecting up to provide the required lap length into the column cage above. Starter bar diameter matches the main column vertical bars. The lap length for compression bars is typically 40–50 bar diameters for C30/37 concrete. Starter bars must be held firmly in position during the footing pour — displacement causes costly remedial work.
A 50 mm thick blinding layer of C10/12.5 lean mix concrete is placed on the bottom of all excavations before reinforcement is fixed. Blinding serves four purposes: it protects the bearing stratum from disturbance and water, provides a clean level surface for reinforcement placement, prevents contamination of the structural concrete, and allows accurate positioning of bottom cover spacers. Without blinding, achieving the 75 mm minimum cover to earth-cast concrete is extremely difficult in practice.
The table below gives indicative reinforcement for common UK pad footing sizes under typical column loads on medium-strength ground (q_allow = 150 kN/m²). All values are indicative — a structural engineer must verify for each specific project.
| Column Load (kN) | Footing Size (mm) | Footing Depth (mm) | Bottom Reinf. (Both Ways) | Concrete Grade | Cover to Earth |
|---|---|---|---|---|---|
| 200 | 1200 × 1200 | 350 | 6T12 @ 200 | C25/30 | 40 mm (blinded) |
| 400 | 1650 × 1650 | 400 | 8T12 @ 200 | C25/30 | 40 mm (blinded) |
| 600 | 2000 × 2000 | 450 | 10T16 @ 200 | C30/37 | 40 mm (blinded) |
| 900 | 2450 × 2450 | 500 | 12T16 @ 200 | C30/37 | 40 mm (blinded) |
| 1200 | 2850 × 2850 | 550 | 14T20 @ 200 | C30/37 | 40 mm (blinded) |
| 1800 | 3500 × 3500 | 650 | 17T20 @ 200 | C32/40 | 40 mm (blinded) |
Follow these steps for every new concrete footing design — from initial ground data through to final reinforcement detailing — in compliance with BS EN 1997-1 and BS EN 1992-1-1 for UK projects in 2026.
Commission or review a ground investigation report (GIR) providing soil classification, SPT N-values or shear strength (Cu), groundwater level, sulfate content, and pH. This is the foundation of all subsequent design decisions — never design a footing without site-specific ground data on a commercial or structurally significant project.
Collect characteristic dead (Gk), imposed (Qk), and wind (Wk) loads from the structural engineer or from take-off calculations. For Eurocode 7 design, use unfactored (characteristic) loads for geotechnical bearing capacity and settlement checks — factored ULS loads are used for reinforcement design per Eurocode 2.
Based on soil type, load magnitude, and site constraints, select the appropriate footing type. Calculate minimum plan dimensions using the bearing capacity formula: A = (Gk + Qk + Wf) / q_allow. Add 10–15% to account for eccentricity and moment transfer. Round up to practical dimensions (50 mm increments).
Set founding depth to satisfy: (a) minimum frost depth (450 mm UK minimum); (b) depth to competent bearing stratum; (c) shrinkable clay depth requirements (NHBC guidelines); (d) proximity to adjacent foundations (45° non-disturbance rule). The governing depth criterion controls.
Verify that the design bearing pressure does not exceed the design resistance of the ground per Eurocode 7 DA1 (both C1 and C2 load combinations). Also check settlement under serviceability loads — total settlement should not exceed 25 mm and differential settlement should not exceed 20 mm for most UK building types per BS EN 1997-1.
Using the factored ULS bearing pressure, calculate the bending moment at the column/wall face and design bottom reinforcement in both directions. Check punching shear at the critical perimeter (2d from column face). Verify minimum reinforcement requirements and anchorage/lap lengths. Detail starter bars for column/wall connections above.
Assign the correct BS 8500 mix designation based on ground exposure class (XC2 minimum for reinforced foundations; XA1/XA2/XA3 for sulfate-bearing ground). Specify nominal cover — 40 mm minimum with blinding, 75 mm minimum without blinding. Confirm cement type requirements for sulfate or aggressive ground conditions.
Issue dimensioned foundation layout plan, section details showing depth, width, reinforcement layout, blinding, cover, starter bar positions, and kicker heights. Include concrete specification, reinforcement grade (B500B per BS 4449:2005+A3:2016), and any special construction requirements (dewatering, temporary support, pour sequence).
For simple domestic construction on uniform soil, Approved Document A Table 10 provides strip footing widths without the need for Eurocode 7 calculations. The key conditions that must all be satisfied for ADoc A to apply:
The primary European standard for geotechnical design — covering bearing capacity, settlement, and all limit state verifications for shallow and deep foundations. Used alongside the UK National Annex for all UK structural foundation design in 2026.
BSI Standards →The UK code of practice for foundations — complementing Eurocode 7 with practical guidance on foundation types, construction methods, ground investigation, and special conditions including shrinkable clay, fill, and contaminated land. Essential reference for UK practitioners in 2026.
ICE — Ground Engineering →Building Regulations Approved Document A provides prescriptive strip footing rules for simple domestic construction. NHBC Standards Chapter 4.2 governs foundation depth on shrinkable clay soils and tree-affected sites — the most common foundation challenge in UK residential construction.
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