Pitched Roofing Underlays

Underlay Selection - Resistance To Wind Uplift

Find the right pitched roofing underlay for your project.

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.

Lightweight underlays and breather membranes have in recent years become commonplace, they offer many advantages over traditional bituminous underlays, however if not correctly secured they can “balloon” transmitting a wind uplift load to the underside of the slates or tiles. A consequence of “ballooning” is that there is an increased risk of the roof covering becoming dislodged.

This issue has been addressed in the updated BS5534 Code of Practice for Slating and Tiling and dependent on the exposure of the roof to wind uplift, batten gauge and the underlay selected it may be necessary to seal the lap of underlay.

A new wind speed map has been produced to accompany BS5534 which divides the UK and Ireland into five distinct wind zones.

 

Non-Breather Membranes

To select the appropriate underlay for your roofing project click on the type of construction applicable to your roofing project below.

Standard roof construction using a well-sealed ceiling 

Roof construction with no ceiling or no well-sealed ceiling 

Roof construction with no ceiling or no well-sealed ceiling and a dominant opening

 

Breather Membranes

To select the appropriate breather membrane for your roofing project click on the type of construction applicable to your roofing project below.

Standard roof construction using a well-sealed ceiling 

Roof construction with no ceiling or no well-sealed ceiling 

Roof construction with no ceiling or no well-sealed ceiling and a dominant opening

Note: The following types of roof constructions 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 a BS5534 Code of Practice for Slating and Tiling.

  • Sealed ceiling construction
  • Warm roof construction with breather membrane fully supported by rigid insulation following the line of the rafter
  • Boarded or sarked roof construction with breather membrane fully supported by plywood or T&G boards (Scottish practice)
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