Basic weathertight design principles

Following the key principles of weathertight design will set the design process on the right path.

Designers need to have a clear understanding of ‘the 4 Ds’ – deflection, drainage, drying and durability – and apply these to house design:

  • How is water deflected from walls and critical junctions by the cladding and design features such as wide eaves?
  • If water gets in, can it drain?
  • If water cannot drain, can it dry?
  • What ensures materials will be durable even if occasionally wetted?

Another approach considers ‘lines of defence’ against water, on the face of the cladding and behind it.

Designers and builders also need to understand the concepts of air movement behind the cladding, and pressure moderation.

Updated: 10 May 2021