CPD Specifier May 2015 issue September 2015 | Page 31

Roofing

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 in 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 complainces and requires very careful choice of roofing underlay.
(Photo: Bradley Cameron for DuPont™ Tyvek®, all rights reserved)

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:
l
l
l

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:
l
l
l
l

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 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.
(Photo: Bradley Cameron for DuPont™ Tyvek®, all rights reserved)

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

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 are in full compliance, not
only with the code, but with all the weathering and thermal performance
expectations of an advanced breather membrane.

DUPONT™ TYVEK® / DUPONT BUILDING INNOVATIONS

TEL: [phone]

WWW.CONSTRUCTION.TYVEK.COM

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