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Ventilation to voids below suspended ground floors is installed to prevent condensation but may also form an integral part of the design for gas protection measures preventing the build-up and aiding dispersal of ground gases, including Radon.
A clear void needs to be provided to precast concrete floors, where shrinkable soils are present, and heave can take place. The amount of void will vary depending on the ground conditions.
300mm void – high volume change potential soils
250mm void – medium volume change potential soils
200mm void – low volume change potential soils
150mm void – in all other cases.
Telescopic vents must be built into the substructure.
Air bricks must follow coursing of the external leaf.
Telescopic underfloor ventilation should be provided at maximum 2m centres.
Telescopic underfloor ventilation should be provided within 450mm – 550mm from corners.
Every air brick must be protected with a cavity tray and 2 weep holes.
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