There is a considerable amount of misinformation in the market place regarding the use of breather membranes in relation to the new amendments to wind pressure requirements of BS 5534 annex A. We have provided the information below in order to assist you in choosing the correct solution for your project and to help clarify the legal requirements of calculating compliance to the new regulations that are currently in place. The key issue that must now be considered is the 5 wind zones which are shown on the map below, but it is important to note that although a project might be shown as being situated within Zone 2 (975 pa) on the UK Wind Pressure Chart Map, any work in a coastal location effectively puts you in Zone 3 (1150 pa). Scotland begins at Zone 3, so it is imperative that you check the correct zone for your project.
A number of design considerations need to be taken into account when constructing new pitched roofs or in refurbishment of existing roofs. One of the functions of an underlay or breather membrane is to reduce the wind load, generated under wind gusts, that acts on the underside of the roof slates or tiles. This issue is addressed in the BS5534 Code of Practice for Slating and Tiling. The selection of the correct underlay or breather membrane is dependent on the exposure of the roof to wind uplift, the type of roof construction specified and roof tile batten gauge. It may also be necessary to seal the lap of underlay. A consequence of the incorrect selection of appropriate underlays or breather membranes is an increased risk of the roof covering becoming dislodged. Note: Boarded or sarked roof construction with breather membrane fully supported by Plywood or T&G boards (Scottish practice) impose no wind uplift conditions on the roofing underlay and as a consequence the underlay selected by the specifier is not subject to the wind uplift pressure zonal classification requirements of BS5534 Code of Practice for Slating and Tiling. We have included the zonal classifications as an increasing number of projects are being specified in Scotland using English practice.
Scotia Roofing Supplies stock a full range of Roofing Breather Membranes as well as Housebreathe in both Forfar and Coatbridge. With weights ranging from 90 grams per sqm to 265 grams per sqm, you are guaranteed to find the correct solution for your project. Our range includes Icopal Monarperm Breathe All Zones, Ultimo, Roofshield, Vista, Maxi and Permavent.