How Tyvek® lasts longer
Unique functional layer
Tyvek® allows water vapour to pass through its natural pores – so a roof can ‘breathe’ – yet keeps water out. This is due to its unique high-quality polyethylene single functional layer comprising millions of microfibres bonded together. Tyvek® is around 6-8 times thicker than ordinary membranes, which makes it much more durable and resistant over time.
Watertightness is key to protection. Underlay must be absolutely watertight (yet breathable) to keep roofs and walls dry. In tests, Tyvek® membranes clearly outperform ordinary alternatives in terms of watertightness to offer lifelong protection.
UV and heat resistance
Most ordinary underlays are made of a microporous film and PP (polypropylene), which is naturally more sensitive to UV than PE (polyethylene). Tyvek® is made of 100% UV- and heat-stabilised PE, which results in superior resistance and durability.
Think twice, build once, trust Tyvek®
A case in point: Multi-layer membrane failure (and subsequent partial roof failure) while a smaller Tyvek® protected section maintains integrity.
Here follows a summary of the ‘real world’ experience of a Homeowner (name withheld by request) in the Czech Republic. This anecdotal report has been gathered and submitted by Pavel Prazak, the local DuPont™ Tyvek® representative, with permission of the homeowner. Pavel encountered the story of the problem with the multi-foil product during a free technical consultation on how to replace that product with Tyvek®.
An unfortunate homeowner, who was undertaking a self-build project, fitted a multi-foil underlay product to his pitched roof in mid-September 2002, in what he claims were warm and dry weather conditions and while following all manufacturer supplied guidelines. He says that the membrane was exposed during the build for a period of 2 weeks until covered.
The brick structure had a roof covering of KM Beta concrete tiles and the 3rd storey (of 3) is a non-occupied attic space with a cold roof system that becomes very warm during the summer. This therefore exposes the membrane to high levels of heat stress, which appear to have been the primary cause of the initial underlay’s subsequent failure in water and air tightness. The second storey of the property is a living area and thus features a warm ceiling system. A vapour control layer was also fitted as part of the system, but membrane tapes were not used.
The primary membrane fitted was a 3 layer (with microporous film) 135 g/m2 underlay. The product name is withheld and no ‘right to reply’ included as the manufacturer has denied that the unbranded product is in fact theirs, despite having first blamed installation methods, which were then proven by the homeowner to have been correct, and despite his invoices, seen by Pavel Prazak naming the product. According to the homeowner, the company subsequently claimed laboratory tests (not seen or independently verified) showed that the product was not in fact theirs and so has refused all responsibility.
During the build, the homeowner began to run out of the initially chosen cheap membrane as the project was nearing completion and so asked his wife to go and buy 1 more roll of membrane. Interestingly she came back with roll of Tyvek® instead of the multi-foil product he’d requested. At first he was unhappy with her choice as it cost a little more. For him it looked like a very thin product and therefore like poor quality … until the other product failed.
The failure of the first product and leakage of the roof into the attic, together with a refusal to accept responsibility by the manufacturer, means that now the homeowner must rebuild the roof, plus the attic floor/warm ceiling below and replace the membranes and cover all other damage at his own expense. The only silver lining has been that the section where the Tyvek® was fitted has survived intact, even after 14 years, and the homeowner is resolved to use (and recommend) only Tyvek® products going forward.
On the second floor living area, the original membrane remains hidden in the ceiling structure so damage has not yet been assessed, but having experienced the issue in attic he is planning to also change that membrane to Tyvek® to avoid any problems in the future. He is now also planning to build a garage with an attic to have some extra storage space, in which he says he will also fit Tyvek®.
Nearly nine years after the 2008 renovation of the roof of a building in Somerset (UK), W1 water column testing revealed some worrying results. Originally designed as a fully boarded cold roof of approximately 4000m², two different underlays had been installed.
- Both products consisted of a top layer of polypropylene spun-bond, a central functional layer (film) and a polypropylene spun-bond as base. The roof slope was approximately 45 and the loft was insulated at ceiling line with fibre glass insulation
In November 2016, specimens of each of the two types of roofing membranes were taken to an independent laboratory for testing.
The basic 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. In parallel, a scale of 1 to 10 (1 being the worst performance, 10 the best) was applied to differentiate between the failing specimens.
Findings showed that after less than 9 years since the roof’s installation, the samples of both multi-layer membranes failed the W1 test.
W1 grade 1 definition: whole surface wet already during filling in H2O, so prior start of measurement. It means it failed immediately upon contact with water.
Roofing membranes are a secondary but vital water-shedding layer.
As such, they should offer long term protection against threats to building integrity such as condensation and infiltration by water and air.
There is a tendency for some tile manufacturers offer long warranty (>30 years) for the tiles, but this doesn’t necessarily take the standard of the roofing membranes they may have selected into account.
Real life tests
In 2016, independent expert Martin Peifer of German consultancy company Steildach-Technik GmbH opened up 30 roofs to take away underlay samples which Kiwa GmbH TBU laboratory then tested for water holdout properties. Their findings are available at www.tyvek.co.uk/rooftest
In 2017, DuPont™ Tyvek® will continue to test and publish more results as they examine roofs across Europe to draw attention to the performance of the different roofing membranes after ‘real life’ ageing.
Compared to other products on the market, Tyvek® breather membranes have shown time and again that they offer unique long-lasting protection against ageing by meeting W1 and surpassing standards.
For more information visit www.construction.tyvek.co.uk