DuPont Tyvek

Reality Check: Independent ‘field’ tests prove DuPont™ Tyvek® maintains vital watertightness after ageing, where many alternative underlays fail

June 14, 2017
  • An independent expert opened up 30 roofs to undertake rigorous water tightness tests on roofing underlays after ‘real world’ ageing
  • 17 Roofs installed with Tyvek® over 20 years ago and 13 roofs with multi-layer or coated roofing underlays installed between 5 and 10 years ago were investigated
  • While the table below shows only W1 (pass/fail), the independent test reporting went beyond the limitations of current standards to check the precise scale of performance
  • Results show troubling failures in water tightness in most of the alternative roofing underlays tested
  • The industry’s reputation and home owners’ investments are at risk as current standards with focus on mechanical stress don’t fully represent reality


Concerned by multiple reports of some alternative vapour-open underlays failing in their secondary water shedding role, DuPont™ Tyvek® instigated a thorough investigation into ‘real world’ performance. When the reputation of a whole class of roofing underlays is at risk because of water tightness failure in some products unable to withstand heat or UV stress, it’s time for the market leader to address the issue.

Independent expert Martin Peifer of German consultant company Steildach-Technik GmbH opened up 30 roofs to take away underlay samples which the Kiwa GmbH TBU laboratory then tested on waterhold properties.


Standards lag behind

As building and industry codes have been working hard to catch up with a rapidly evolving market, assessment methods such as those within standard EN13859-1&2, still lag behind in evaluating vital issues such as actual longevity. Qualities such as long term water hold out – which most crucially affects the homeowner – must be assessed after exposure to natural environmental stresses, both during the build and when occupied.

Increasingly vapour-open but decreasingly fail-safe?

While ageing of underlays can positively affect vapour diffusion with increased porosity, this may adversely affect the water shedding function, should the primary covering fail. This unfortunate occurrence is becoming more prevalent in today’s increasingly stormier weather. Ultimately, the primary quality in terms of longevity is water tightness – an area which presents the most risk for property, insurance, and reputations.

Test methods:

The EN13859-1&2 W1 classification system for water tightness was used. Each specimen was exposed to a 20cm water column for 2 hours to measure not only whether any leakage occurred, but how much, over what surface area and how quickly. This established, in crucial and revealing detail, precisely how well each underlay withstood water after 5 to 10 years in a roof, or, in the case of Tyvek®, for more than 20 years. For more details on the test methods and results please see this link:


The table shows the W1 results of all 17 Tyvek® roofing underlays and all 13 alternatives (green equals pass)

Based on the results above the picture is as follows:

  • 13 out of 17 Tyvek® roofing underlays can be declared watertight after more than 20 years
  • 0 out of 6 multi-layer microporous film based roofing underlays can be declared watertight after less than 10 years
  • 2 out of 7 coated roofing underlays can be declared watertight after less than 10 years


Even without factoring in the age differences (the Tyvek® samples being significantly older than the other installed products), Tyvek® clearly emerges as the most reliable in terms of crucial water tightness, while there is significant cause for concern with alternative roofing underlays.


A case in point: Multi-layer membrane failure (and subsequent partial roof failure) while a smaller Tyvek® protected section maintains integrity.

Read the case study >