Raft Foundation Volume

Radier (mat) foundation volume

A radier (mat foundation) is a single reinforced-concrete slab that takes the place of individual footings and spreads the building load across the whole footprint. Thickness usually runs 10–15 cm for residential work and 20 cm or more for commercial and industrial. You reinforce it with welded wire mesh (Q138, Q196) or a rebar grid, and the concrete is typically fck 25 MPa. The volume is width × length × thickness, with a 3–5 % overage added on for waste and irregularities. Take 10 × 15 m at 15 cm: that's 22.5 m³ raw, or about 23.6 m³ once you tack on the 5 %.

Applications and standards

It's a good fit for soft soil with low bearing capacity, popular housing (Minha Casa Minha Vida), industrial sheds, service areas, and any situation where pad footings would end up covering most of the area anyway. The governing reference is NBR 6122 (foundation design). You'll still need a soil investigation (SPT) to confirm the bearing pressure, plus a structural designer to set the thickness and reinforcement.

FAQ

When is radier better than footings? On soft soil, or when the footings would sit very close together. At that point the radier usually comes out cheaper and more uniform.

Do I need a vapor barrier? Yes. A polyethylene film laid between the soil and the concrete keeps moisture from rising into the slab.

Can the radier be the finished floor? Yes, given a power-trowel finish. That's a common approach in sheds and service areas.