Journal

Rain Screen Technology

Dr. G B Walford, NZ Forest Research Institute Ltd

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 so unnoticed, provided the interior lining does not collapse first.

This paper explores this problem and offers one solution in the form of “the 4 D’s” :

  • Deflection
  • Drainage
  • Drying
  • Durability

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