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BS 5534 Changes and the implications to the industry

TWENTY YEARS AGO THE UK’S TOP PERFORMING VAPOUR PERMEABLE UNDERLAY, ROOFSHIELD, WAS NOT EVEN LAUNCHED. EVERYONE WORKED TO BS5534:1990:PART 1 (25 PAGES - NOW 173) AND IF YOU WERE LOOKING FOR A ROOFING UNDERLAY YOU HAD THE CHOICE OF EITHER BITUMEN FELT, SINGLE LAYER NON-WOVEN POLYPROPYLENE MEMBRANES, FLASH SPUNBOND OR REINFORCED POLYETHYLENE’S WITH MICRO PERFORATIONS.

The only permeability requirement was in fully supported applications and was only 36g/m2/day in accordance with BS3177. For underlays not fully supported the recommendations were to use BS747 bitumen felt and if using a polyethylene film of 0.13mm the batten gauge should not exceed 100mm.

Twenty years on

Fast forward to 2015 and vapour permeable membranes are now used on most projects in the UK. Over this time, VPUs (now typically with MVTRs greater than 1000g/m2/day) have allowed ventilation requirements for roofs to be reduced to ridge-only, or for high performance air permeable membrane such as Roofshield, eliminated.

Alongside this evolution in technology, climatic factors affecting roof design have also changed, with extreme weather conditions occurring more frequently. The increasing likelihood of violent storm conditions has demanded a more rigorous approach to roof design, amid a growing recognition that the old principles are no longer fit for purpose.

The recently published BS5534:2014 reflects this with more rigorous design standards for both the fixing of roof coverings and the robustness of underlays of all types.

Traditional methods such as mortar bedding of ridges can no longer be relied upon to resist wind loadings, therefore designers and roofers will need to familiarise themselves with the new requirements, and seek updated fixing schedules from material suppliers.

For underlay classification the country is split into 5 wind zones as shown:

Manufacturers must now clearly state in which zones their underlays are suitable, and if any special installation conditions apply. These specifics may include, taping of lap joints, variations in batten gauge or reduced batten spacing in higher wind load zones. The new BS5534 should be embraced by the industry and recognised as a raising of standards and producing less problems on roofs due to wind damage.

Based on independent testing, Roofshield continues to demonstrate its performance by being compliant throughout the whole of the UK.

For zones 1-3, no special measures are required, beyond ensuring laps are extended to coincide with slate or tile battens. For zones 4 and 5, designers and roofers should consult the A Proctor Group to review the specific application, however for the majority of fully supported applications (commonplace in these geographic areas) no special measures will be required. If necessary, a detailed specification will be issued giving the options for compliant installation.

While significant changes to long established standards are a source of upheaval and concern to the industry, embracing these changes can only be of benefit, reducing the likelihood of problems and remediation.

By continually improving our product ranges, the A. Proctor Group aim to make the transition as painless as possible for our customers. For further information on Roofshield, and the implications of the new BS5534, please visit www.proctorgroup.com.