STANDARDS AND INSTALLATION STANDARDS

The British standard for the installation of underlays in roofs is the British Standard for the Control of Condensation in Buildings; BS 5250:2002 This is referenced in relevant sections of the Building Regulations in England and Wales, (Approved Document c). Scotland (standard 3.15) and Northern Ireland (Technical Booklet c). An amended version of BS 5250:2002 was issued in December 2005 and these should now be followed.

UV RESISTANCE

Although Strotex has a high UV resistance it is specifically recommended to cover the membrane as soon as possible with permanent roof tiles.

WARM ROOF APPLICATIONS

BS 5250:2002 states there must be an adequate flow of air through the batten space when a breather membrane is used in a warm roof application. With most roof tiles and slates these provide enough ventilation but if an airtight tile or slate is used batten space ventilators should be installed. Counter battens will not normally be needed when the membrane is laid unsupported with drapes but counter battens will be

required when the membrane is fully supported on insulation.

COLD ROOF APPLICATIONS

In order to work effectively it is important that breather membranes are laid so that the space between the membrane and roof covering allows for adequate ventilation. Tiling battens should therefore be at least 25mm thick to ensure an adequate airspace between the membrane and final roof covering to allow water vapour to disperse. Counter battens are not normally required in a non ventilated cold roof as there should be adequate airflow between roof tiles or slates. However if an unusually airtight final roof covering is used then batten space ventilators and counter battens should be used.

Ref: BS 5250:2002

The final roof covering manufacturer’s advice should be sought on their products air openness when installed.  In non ventilated cold roofs consideration must be given to providing a vapour control layer and vapour check plasterboards to maintain a convection tight ceiling. All penetrations will require sealing including any loft hatches. The building below the roof void should be ventilated in accordance with national building regulations and standards. Extractor fans should be used in rooms with above average humidity and all water tanks should be covered and pipes lagged in the roof void. Advice should always be sought from Local Authority Building Control on the design and installation of ventilation systems with particular regard to cold roofs.