Water tightness testing reveals roofing underlay weaknesses

Concerned by water tightness failures in alternate roofing underlays, DuPont Tyvek instigated an independent field test to examine the ‘real world’ performance of its systems.

After hearing reports of alternate vapour-open roofing underlays leaking, DuPont Tyvek issued an investigation into the ‘real world’ performance of these systems.

Martin Peifer, an independent expert of Steildach-Technik GmbH, was contracted to collect underlay samples from 30 different roofs.

These roofing underlays were exposed to rigorous water tightness tests at the Kiwa GmbH TBU laboratory; the tests were designed to examine how each underlay has aged in the ‘real world’.

Whilst the ageing process can have a positive impact on vapour diffusion, it can adversely affect an underlay’s water shedding function should the primary covering fail. In stormier weather, this is a common occurrence.

Water tightness testing

Each sample was subjected to a 20cm water column for two hours. Experts assessed whether any leakage had occurred; if so, how much, over what surface area and how quickly. The EN13859-1&2 classification system for water tightness was used to determine how well each roofing underlay endured water after 5 to 10 years in situ.

Following the tests, 13 out of the 17 Tyvek underlays examined were declared watertight, after more than 20 years in a roof. The Tyvek samples were significantly older than the other installed products, demonstrating their durability.

Meanwhile, 2 out of the 7 coated roofing underlays tested could be declared watertight after less than 10 years; none of the multi-layer microporous based roofing underlays achieved water tightness.

Long-lasting roofing underlays

DuPont Tyvek argues that a roofing underlay’s primary quality, in terms of longevity, is water tightness – underlays which fail to provide this are putting property and insurance at risk.

The company believes that current building and industry codes, with their focus on mechanical stress, are misleading. Homeowners are more likely to benefit from long-term water hold out; assessment methods still lag behind in evaluating this.

DuPont Protection Solutions
BBSP1
Bristol & Bath Science Park
Dirac Crescent
Emersons Green
Bristol
BS16 7FR

Phone: 08444 068 722

Technical enquiries: Tyvek.construction@dupont.com

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