Foundation slab
Marketed as a revolution. Structurally, it is simply a monolithic reinforced slab in place of footings and foundation walls. When it makes sense, and when to stick with footings.
Written by Marta Published Updated
What it is
A foundation slab is a monolithic, reinforced concrete slab on which the entire structure of the house sits directly. It replaces traditional strip footings with foundation walls.
It is most often used in the bottom-insulated variant — with a thick layer of XPS or EPS200 under the slab providing thermal insulation in place of a foundation wall.
When it makes sense
- Poor soil bearing capacity — the slab distributes load over a larger area; footings would need to be deeper and wider
- High groundwater level — easier to seal a single continuous surface than a wall system
- A single-storey house with large glazings — when you want a minimal plinth height on the garden side
- Wet underfloor heating on the ground floor — the slab pairs naturally with embedded pipework
When footings are still better
- A steeply sloped plot — levelling the ground for a slab gets pricier than building taller foundation walls
- Plans for a basement — by definition the slab has no basement; if you need one, you go with footings
- A tight shell budget — for a simple, rectangular house on competent soil, footings can be 15–25% cheaper
In short: a foundation slab is a very good solution for specific geotechnical conditions and a specific programme. It is not automatically the better option — the choice always follows from the soil survey, the design and the budget.