Vapor Permeable Air Barriers
Light timber framing has evolved to use a flexible synthetic material on the outside face of all external walls as a way of achieving air-tightness (and as a secondary defense against moisture ingress).
The use of vapor permeable air barriers (colloquially referred to as building wrap, house wrap, wall underlay and/or building paper) under cladding materials emerged in the late 1800’s (Issacs, 2015). At this time the material of choice was a newly invented tar impregnated paper product (now referred to as bituminous building paper) (Issacs, 2015). At the time of invention and continuing to today the primary purpose of ‘building paper’ is to minimize drafts. And although commonly used in New Zealand and Australia during the early 20th century it’s use wasn't made mandatory until NZS 1900 in 1964 (Issacs, 2015). The specific technical requirements of vapor permeable air barriers are covered in NZS 2295:2006.
SPECIFICATION
The majority of vapor permeable air barriers available today are made from non woven spunbond polypropylene (BRANZ, XXX).
ProClima, who provide higher specification vapor permeable layers, use thermoplastic elastomer-ether-ester (TEEE) between two layers of polypropylene microfibre fleece (ProClima, 2015).
END OF LIFE
DuPoint, makers of Tyvek (possibly the worlds most common building wrap) claim that their product can be recycled at end-of-life. Tyvek, being a category 2 (PP) plastic means that high-value recycling is possible, however Tyvek is not accepted in kerbside recycling schemes. DuPoint only takes Tyvek material for recycling when returned directly to Tyvek’s factory. This makes the recycling of any Tyvek product extremely unlikely outside of major manufacturing centers.
ThermaKraft operates a manufacturing plant in Auckland, New Zealand and distributes its vapor permeable air barriers around both Australia and New Zealand. On almost all of ThermaKraft’s product deceleration literature it is noted that their house wraps are recyclable and do not emit VOC’s (Thermakraft, 2016).
By weight vapor permeable air barriers make up very little of a buildings end-of-life waste (<0.5%).
Contamination Issues
One of the major challenges