Mesh Specification Selector Guide | Which Mesh for Your Project?

How Do You Reinforce a Strip Foundation?

Strip foundations carry wall loads down to the bearing stratum. A typical domestic strip is 600 mm wide and 600–900 mm deep, depending on soil type and NHBC Chapter 4.2 guidance. On clay soils, depth increases to get below the zone of seasonal moisture change.

Standard reinforcement: T12 bars top and bottom, running the full length of the strip. The engineer specifies the number of bars per layer — typically 2 or 3 T12 bars per layer for a 600 mm wide strip. T8 links at 250–300 mm centres hold the cage together and resist shear. Cover to all bars is 50 mm minimum in contact with ground (BS 8500 exposure class).

For a single-storey extension with 12 linear metres of strip foundation: approximately 48 m of T12 bar (4 bars × 12 m) plus 40 T8 links. At £6.79 per 6 m T12 bar, the main bar cost is around £54. Links add roughly £30. Total rebar cost under £85 — a fraction of the concrete and excavation cost.

What Reinforcement Goes in Pad Foundations?

Pad foundations sit under individual columns or point loads. Each pad is a square or rectangular block of reinforced concrete, typically 450–750 mm deep and 600–1,500 mm across. The size depends on the column load and the ground’s bearing capacity — the engineer calculates both.

Reinforcement is a mat of bars in both directions at the bottom of the pad. T16 or T20 bars at 150–200 mm centres are standard for domestic steel-frame or post-and-beam structures. The bars run full width with 50 mm cover on all faces. Some engineers specify a top mat too, especially on deeper pads where the column applies moment as well as downward load.

A 1,000 mm × 1,000 mm pad with T16 at 150 mm centres both ways needs 7 bars each direction = 14 bars total. At 1 m length each, that is 14 m of T16. At £10.95 per 6 m bar, roughly £33 in rebar per pad. Starter bars (T16, 1 m long, shape code 38 cranked) project up from each pad into the column above.

When Should You Use a Raft Foundation and How Is It Reinforced?

Raft foundations spread the building load across the entire footprint. They are used on weak ground (bearing capacity below 50 kN/m²), variable fill, or high-plasticity clay where strip foundations would need to go deeper than 1.5 m. The raft avoids deep trenches and reduces differential settlement.

A domestic raft is typically a 250–400 mm thick slab with thickened edge beams (500–600 mm deep) around the perimeter and under loadbearing walls. The slab uses A393 mesh top and bottom — two layers giving 7.86 cm²/m of steel area in each direction. Edge beams use T16 or T20 longitudinal bars with T8 links at 200 mm centres.

For a 60 m² raft: the slab needs roughly 17 sheets of A393 mesh (top layer) plus 17 sheets (bottom layer) = 34 sheets at £42.98 each = £1,461 in mesh. Add T16 bars for edge beams and starters. A raft costs more in steel than strip foundations, but saves on excavation depth and is often the only viable option on poor ground.

How Do Starter Bars Connect the Foundation to the Wall Above?

Starter bars are short lengths of rebar cast into the foundation with their top portion projecting above the concrete surface. They create the structural connection between the foundation and the wall, column, or ground beam above. Without starters, the upper structure sits on the foundation with no tensile continuity.

For masonry walls on strip foundations, starters are T12 bars at 450 mm centres, projecting 500–600 mm above the foundation top. They are bent into an L-shape (shape code 32 to BS 8666:2020) with the horizontal leg tied to the foundation cage before the pour. The vertical leg is later built into the blockwork bed joints or tied into the ground beam cage.

For columns on pad foundations, starters match the column bar size — typically T16 or T20. Four starters per column is standard on domestic work. Each starter has a 90-degree crank at the bottom (shape code 38) and is tied to the pad reinforcement. Starter bar lap length with the column bars above: minimum 40× bar diameter. For T16, that is 640 mm of overlap.

What Does Building Control Inspect at Foundation Stage?

Building Control inspects foundations before any concrete is poured. This is a mandatory inspection under the Building Regulations — you must give your Building Control body at least 24 hours’ notice before the pour date. Pouring without inspection means the inspector may require the concrete to be broken out for re-inspection.

The inspector checks: trench depth reaches the bearing stratum shown on the engineer’s drawings, trench bottom is clean and level, reinforcement matches the structural engineer’s specification (bar sizes, spacing, cover, lap lengths), spacers are in place to maintain cover, and no bars are displaced or missing. They will compare the steel on site against the engineer’s approved drawings.

Keep these documents on site for inspection day: structural engineer’s foundation drawings, bar bending schedule (BS 8666:2020), Building Regulations approval notice, and steel delivery notes showing CARES certification and B500B grade. The inspector may photograph the reinforcement before approving the pour. If the rebar does not match the drawings, the pour is stopped until corrections are made.

Important: This guide is for general information only. All structural reinforcement must be specified by a qualified structural engineer. Always follow the engineer's specification and relevant British Standards for your project. NextDaySteel supplies materials only.