Garage Conversions - the vital use of a Vapour Barrier
Most garage conversions will require thermal upgrading of the floor, walls and roof which
will also incorporate the use of a vapour barrier. These insulation levels are fairly high compared to previous
times and as the warmth within a room increases, its ability to hold higher levels of water vapour also rises. As
the warm moisture laden air passes through the garage conversions building fabric unchecked there is a possibility
of interstitial condensation forming within the insulation or other material causing long term damage.
This risk can be minimised by installing a vapour barrier to the warm side of the insulation. Although it does
not stop or prevent the passage of heat through the insulation or structure the moisture laden air is stopped or
resisted. Many building products used for the upgrade of a garage conversion already contain a built in vapour
Most composite insulated plasterboards for the thermal dry lining will incorporate a vapour barrier these days.
If the do not then a vapour barrier needs to be aped manually always ensuring that it is applied to the warm side
of the insulation and NOT the cold side. This aspect of its positioning can be a cause for concern for some
homeowners not understanding the science or mechanics of condensation.
Every year hundreds of garage conversions (usually the DIY ones) have the vapour barrier positioned incorrectly
causing even more potential for damage to the garage conversions building fabric. The requirement for a vapour
barrier to be installed within the floor, walls and roof of a garage conversion is a requirement under building
The materials for a vapour barrier within a garage conversion can be polythene sheet or a metal foil. Metal
foils are usually more effective than polythene in most cases for preventing the passage of warm moist air.
Attention and care needs to be taken for ensuring adequate laps and sealing of joints and abutments. CICA make
special tapes and sealing agents specifically for this task that do not dry out or go brittle over time.