Could the altitude clause in BS5534 leave some contractors high and dry?
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 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 and Nottinghamshire? 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?
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 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/M2 when 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®.
All three BBA approved underlays in the group: DuPont™ Tyvek® Supro, DuPont™ Tyvek® Supro Plus (with integral tape) 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.
Kevin Taylor, Technical & Training Manager of the National Federation of Roofing Contractors, comments “Of all the main changes to BS5534, the testing and classification of underlay has caused the most confusion out there in the industry. What roofing contractors and designers are looking for is clear guidance from the manufacturers on which underlay to choose in any given situation, and ideally, to identify types of underlay that will comply for any roof they work on in the UK, irrespective of things like zones, batten gauges, altitude, location and the condition of the ceiling inside the building. It is very encouraging therefore, when companies like DuPont are able to state that their underlay does just that, without any ifs, buts or maybes.”
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Our current Tyvek® pitched roof underlays listed below have been subjected to the test procedures concerning wind uplift outlined in the recent revision to BS5534 (Code of practice for slating and tiling).
These products are currently available, are fully BBA certified and have full CE marking and Declaration of Performance (DoP) as required under the Construction Products Regulations 2013.
Tyvek® Supro, market-leading breather membrane, helping to protect roofs against wind and water, and also improve energy efficiency
Tyvek® Supro Plus, offers the same benefits, plus an integral adhesive lap tape designed for use in the Tyvek® sealed roof system.