Suspended floors for a house extension 

Suspended timber floors have a myriad of gaps around the boards, at the junctions with walls (internal and external) and around service pipes. Air can leak down through these gaps into the unheated floor void. Large area boards and tongue-and-groove edges can reduce air leakage, but it is essential to seal all the gaps and holes before floor coverings are laid.

Beam-and-block floors may have a large number of gaps and cracks, particularly if the screed is poor. Major areas of air leakage are around the edges and at service entry points (water pipes behind baths, sinks and WCs). Often one or more blocks are omitted, or large holes are cut through them, in order to allow the pipes to pass through the floor. These large holes are hidden from view by bath panels, sink pedestals, vanity units, floor coverings, etc.