BS 5250:2002 AMD1 defines a well-sealed ceiling as follows:
The design avoids constructional gaps, especially at the wall ceiling junction with dry lining construction, and holes in the ceiling.
No access door or hatch should be located in rooms where large amounts of moisture are produced, including kitchens or bathrooms. The air leakage rate through an access hatch, including its frame, when tested to BS EN 13141-1:2004 4.3 is less than 1 m3/hr at a pressure difference of 2Pa. It can be assumed that “push-up” wooden hatch covers in a frame, constructed in-situ, with continuous compressible seals, will meet this criterion provided the weight of the door is at least 5.5 kg. Hatch covers should either be heavy enough to compress a seal or be clamped, with closed cell compressible seal, or “o-ring” between it and the frame. Drop-down hatch covers are more difficult to seal; it is recommended that propriety units with a supplied hatch cover in a frame are used. Manufacturers can provide third party evidence that the leakage criterion is met.
Penetrations, such as those for services and rooflights, are permanently sealed with suitable proprietry products.
The ceiling is sealed to the external walls to limit any leakage through cracks.
Recessed light fittings should comply with BS EN 60529 and be rated IP60 to IP65 (depending on room use), or incorporate an appropriate sealed hood or box which meets the following test criteria. The total leakage through downlighters should not exceed 0.06 m3/h.m2 of ceiling at 2 Pa.
The head of all cavities in the external walls, party walls and partition walls is sealed to prevent transfer of warm moist air into the loft.
