Concrete frame · ground floor base
Base of the wall on a ground-bearing slab — perimeter insulation wrapping the slab edge and lapped damp barriers keeping the ground out.
Components
- 1Rainscreen cladding — stopped clear of the ground
- 2Cavity base flashing & weep holes
- 3Continuous external + perimeter insulation
- 4Ground-bearing floor slab
- 5Sub-slab insulation
- 6Strip foundation / thickened edge
- 7DPM lapped to the wall DPC
- 8External ground level — below internal floor level
- 9Aluminium carrier rail
- 10Thermally-broken bracket — bolted to the wall, isolated
Why it works
Carry the external insulation down past the slab edge and lap it to the sub-slab insulation. Stop it at ground and the slab perimeter goes cold — condensation and mould collect exactly where the floor meets the wall.
The damp-proof membrane under the slab must lap up and join the wall's damp-proof course. Together they form one unbroken barrier so ground moisture can't rise into the slab or wick up the wall.
The rainscreen sheds most water; whatever gets past it runs down the back of the cladding and out through the open cavity. The cavity must stay drained and ventilated at every floor — never sealed solid — or trapped water saturates the insulation.
Set the internal finished floor level above external ground and stop the cladding clear of the ground. Splashback, puddling and snow then can't bridge the damp protection or stain the cladding.
Common mistakes
- Insulation stopped at the slab edge, leaving a cold perimeter and condensation where the floor meets the wall.
- DPM under the slab not lapped to the wall DPC, so ground moisture rises straight past it.
- External ground built up above the internal floor, bridging the damp protection.
- Cladding taken down to the ground where splashback soaks and stains it.