Rain Screen Technology

The system of exterior cladding for timber frame buildings that uses stucco is being used very widely in New Zealand - sometimes with disastrous results. Likewise with stucco or sprayed-on textured coating over polystyrene foam - called "chillybin" construction. In the Northwest United States and in Western Canada similar construction has led to losses running to billions of dollars. That part of the world has high rainfall, like much of New Zealand. The problem lies not with the materials so much as with the system. What has happened is that water has penetrated the exterior cladding and has been unable to drain away, or to evaporate. Untreated timber in contact with moisture and warmth is bound to decay and it will do unnoticed, provided the interior lining does not collapse first. Boric treated timber will stand occasional but not continuous wetting. Typical construction uses building wrap over the timber frame and fibre-cement sheet, followed by stucco. The use of reinforced plastic TYVEK building wrap is an improvement over building paper but not the complete answer because it is inevitably punctured by nails and staples. BRANZ (2001) has also just published an article on this, pointing out that "there has been little research done as yet in New Zealand.....the following is the best advice we can give at the present".