Housewrap and other air barriers

Housewrap such as Tyvek and Typar were perhaps the first commercially available air barriers or membranes made to stop air leakage through the building envelope. Since their introduction, many new products have become available that take the breathable air barrier one step further.

Moisture control is perhaps the most important consideration in modern construction. Every year there are billions of dollars spent on litigation related to the effects of water getting into buildings. The permeable membrane has become one of the most important technologies in keeping water out of buildings while at the same time, allowing the passage of air to prevent the buildup of mould.

Membranes are made of multi layer spun bonded materials that have openings large enough for air molecules but too small for water molecules to pass through. A typical menbrane might have 6 to 7 times the permeability to air than a relatively impermeable material such as plastic house wrap.

One of the disadvantages of roofing membranes is that only a few companies specialize in the technology. European companies currently dominate their manufacture. North American suppliers must often incorporate european membranes into the their own fabricated materials if they want to offer membrane technology to their customers.

There are traditional materials such as asphalt based tar papers which have some moisture control properties but are heavier to handle and do not allow air circulation. House wraps ans plastic based sheets may be easy to handle but still do not allow the building to breathe. There are also expanded plastic materials which allow air circulation but cannot control water infiltration.