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The 4Ds of Durabilty

When choosing materials for use in buildings, a risk assessment approach referred to as the 4Ds of weathertightness design is followed.

Based on work undertaken in Canada, it has been adopted into the Compliance Document E2/AS1 which is the Acceptable Solution for achieving the Building Code Clause E2 External Moisture.

 

The 4Ds refers to :

  • Deflection – keeping water away from potential entry points.
  • Drainage – providing a means  for water removal that does enter.
  • Drying – allowing any remaining moisture to be removed by ventilation or diffusion.
  • Durability – providing materials with appropriate durability.

The Acceptable Solution E2/AS1 document includes guidance on potential weathertightness risks for buildings and how these can be managed or reduced using the principles of the 4D’s. 

Using the risk matrix with nominated cladding types and the inclusion of a drained cavity for external walls in higher risk situations, is one option of achieving weathertightness.
 
The prevention of biological degradation affecting the structural integrity of timber in-service, e.g. wall framing, is achieved primarly by keeping the wood ‘dry’, or by using preservative-treated or naturally durable timber where the timber may be exposed to intermittent moisture or be potentially in damp conditions. 

However, combinations of wood-based building components with other materials, e.g. cladding type, and the type of design, e.g use of wall cavities, has a signficant effect on the choice of wood product.

NZS 3602 provides guidance on the wood product options to achieve 5, 15 or 50 year durability performance.

 

For more information on the durability requirements for the following building elements, download Durability information for specifc end-uses - Printable PDF

  • Fascia.
  • Weatherboards.
  • Joinery.
  • Fencing.
  • Decking.
  • Crib walls.
  • Piles.
  • Poles.