ROOFING NORTH WALES

Many flat roofs have been constructed with little or no thermal insulation. Not only does this mean a higher heating bill to keep the room(s) warm but also there may be an accumulation of moisture within the roof structure that can lead to rotting of the structural timbers, and even poorer thermal insulation if the insulation becomes wet.

The solution is to retain as much of the existing structure as possible (assuming no rot) and add extra insulation, a vapour barrier and a new top weather-proof surface.

Wherever warm moist air meets a cold surface condensation can be a problem. If this occurs within the roof space it will cause damage and neutralise the effectiveness of any thermal insulation. See the section on Interstitial condensation.

First, the existing waterproof roof surfacing must be removed. This is usually 3-ply felt. Then a vapour barrier of 125 micron polythene is laid to prevent moisture from inside the room entering the thermal insulation. This construction complies with British Standard BS5250:2002 ‘Code of Practice for control of condensation in buildings’. Next, rigid foam thermal insulation panels are laid. Finally the new flat roof surface is fixed in position. This comprises OSB (Oriented Strand Board) - more commonly called 'Sterlingboard'. Finally, the weatherproof top surfacing, which may be EPDM rubber, 3-ply felt or GRP (Glassfibre Reinforced Plastic). See the section on Flat roofs for more information on surfacings.