Could the altitude clause in BS5534 leave some contractors high and dry? Better to choose your underlay very carefully…

BS5534:2014 highlights the role of a roofing underlay’s wind uplift resistance in protecting against stormy weather and preventing costly damage. The considerations it outlines (based on a combination of meteorological, geographical and building physics data) not only establish the minimum standards in the new code of practice, but are also essential to long term peace of mind.

However, while much is being made by various underlay manufacturers and suppliers of achieving BS5534:2014 compliance, the picture may not be quite so straightforward – especially when you consider that a key part of the revised standard refers to altitudes not greater than 100m – and that large areas of the UK are at often surprising heights above sea level.

For example, one might expect parts of Cumbria, Wales and Scotland to exceed that benchmark… but how about Milton Keynes? Or swathes of Essex, Surrey, Nottinghamshire and Northern Ireland? Could this factor expose some unsuspecting developers and contractors to unnecessary risk and make them vulnerable to falling short of the code – and therefore potentially liable in any insurance claims?
Many parts of the UK & N. Ireland are at an altitude that exceeds the 100m above sea level benchmark stated in the new BS5534:2014 code of practice, which may affect compliance and requires very careful choice of roofing underlay.
With world weather looking increasingly unpredictable (and litigation on the rise) anyone specifying a membrane would do well to ensure that, like their project’s roof, everything is covered by a membrane with proven reliability and compliance with all conditions, altitude included.

All underlays are required to clearly state, in literature, certification and on roll labels, the declared wind uplift of the material, and on this basis, the end user can determine the suitability of the material for the site’s location. BS5534 splits the UK (including Northern Ireland) into 5 zones, and to be “fully compliant” at a batten gauge of 345mm, the following test parameters must be met:

  • 1,600 N/M2 when a well sealed ceiling is present
  • 1,900 N/m2 when no ceiling or no well sealed ceiling is present
  • 2,350 N/M2when no ceiling or no well sealed ceiling is present and a permanent dominant opening is present on an external face of the building

But, is it that simple? The new standard also requires compliance with the following conditions:

  • Ridge height not greater than 15m
  • Roof pitch between 12.5° and 75°
  • Site altitude not greater than 100m
  • No significant site topography

Clearly, comprehensively meeting all the requirements of BS5534:2014 could prove challenging for contractors also looking for a reliable, easy-install, trouble-free solution. Fortunately, however, there are products which allow unrestricted use anywhere in the UK, in all building characteristics and under all site conditions. Unsurprisingly these come from a name well-known for over 25 years for proven quality, durability and service: DuPont™ Tyvek®.
Peace of mind: All 3 BBA approved DuPont™ Tyvek® roofing underlays are fully BS5534 compliant, allowing unrestricted use anywhere in the UK & Northern Ireland for all building types under all site conditions.
All three BBA approved underlays in the group: DuPont™ Tyvek® Supro, DuPont™ Tyvek® Supro Plus (with integral tape) and DuPont™ Tyvek® Enercor roof offer unrestricted application when tested in accordance with BS5534:2014 – and with no counter battens required in any zone. This allows contractors to be confident that they in are full compliance, not only with the code, but with all the weathering and thermal performance expectations of an advanced breather membrane.

For further information, literature is available to download at www.construction.tyvek.com and expert technical assistance is available on Tel. 01275 337 660, option 2 (in Northern Ireland and ROI please call: 087 922 2740)

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