Airtightness is much more than just the right product, it’s the right system…
Architects, builders, developers and savvy home buyers are beginning to understand not only the importance of airtightness, but also the potential complexity in getting it right. There is, however, a very simple solution: work with a proven system of carefully developed and tested products – and the expert team behind them.
Recently, a project to bring key membranes, AVCLs, tapes, sealants – and vitally – correct installation methods together into one ideal ‘passive house’ demonstration was undertaken at BRE (Building Research Establishment), with assistance from DuPont. The results “impressed everyone”, according to Nick Williams, DuPont™ Tyvek® Technical Manager UK & ROI, who facilitated the project and emphasises that, “we also know that with new product developments, or different DuPont product combinations, the performance could be even better.”
As part of its customary standards of independent and thorough testing, the BRE built a compact timber structure on site. The following products were then fitted, taking great care to correctly install and properly seal at laps and penetrations, and in all corners, curves and awkward spaces: Tyvek® Supro to the roof, Tyvek® HouseWrap to the exterior of the walls, AirGuard® Control AVCL to the interior of the walls, Tyvek® tapes throughout the construction, plus the newly launched Tyvek® FlexWrap EZ tape to windows, doors, rafters, floors, etc.
Once the test structure was complete, a blower door was fitted and the structure pressurised to the industry standard 50Pa. Test results were recorded after each stage of completion. The final tests were conducted when the latest low emissivity Tyvek® membrane was fitted as the external wall membrane. This resulted in an extremely impressive figure of 0.12 m3/hr/m2 @50Pa (0.24 ACH), well below the Passivhaus standard which in itself is a difficult level to achieve.
According to Dr Paul Blackmore, Associate Director, Fire and Building Technology Group
BRE, “The testing showed the importance of maintaining an airtight barrier around the test building to prevent unintended air infiltration/exfiltration. The DuPont™ Tyvek® and AirGuard® membranes and tapes provided an almost complete air tight seal around the walls and roof of the test building.
The air leakage measurements with the test building wrapped in DuPont membranes with DuPont tapes were as low as 0.12 m3/hr/m2 and 0.24 ACH @ 50Pa which significantly exceeds the air tightness requirements of the Passivhaus standard for low energy buildings.”
The imperatives of a variety of regulations are one thing, but the key drivers are emerging from the market itself and from the appreciation that airtightness brings not only sustainability benefits but also increases both cost-efficiency and occupier comfort. Current UK regulations call for air leakage figures below 10 m3/hr/m2 @50Pa and controls are bound to get only get stricter in the future, while the benchmark Passivhaus standard is 0.6 ACH, equivalent to around 0.3 m3/hr/m2 @ 50Pa.
A vital lesson, both from the BRE exercise and experience in the field, is that while airtightness can be straightforward to achieve using the right products and systems, there can be no weak link in the chain. A reduction of specification quality at any aspect of the envelope, a key step or process missed, or any careless or incorrect installation and the results will be as disappointing as the waste of time or money. There is simply no substitute for quality and expertise, and cutting corners – or failing to seal them properly – just doesn’t work. Furthermore, even with the best products and the best will in the world, those ‘hard to reach’ areas will also need special attention.
This is where the holistic approach from DuPont becomes even more indispensable, with the joined-up thinking of products such as Tyvek® FlexWrap tapes, which are designed to expand, contract, bend and shape concertina style, to fit into any awkward area to be sealed. A new version of the product, Tyvek® FlexWrap EZ, is about the hit the market, bringing even further benefits for both performance and installation to the new generation of responsible construction.