The Six Principles of Weathertightness

Some time ago some Canadian weathertight specialists were invited to visit New Zealand to share with local building industry representatives, their experiences of the Canadian version of our "Leaky Home syndrome".
One of their conclusions, was that there needed to be a set of principles that designers of claddings and the like, ought to follow to ensure good design that would prove successful over the years. These principles were described as the "4 D's" and have been adopted by the New Zealand Department of Building and Housing (DBH)
 
According to the DBH web site, the 4Ds as referenced in E2/AS1 are:
    * Deflection - keeping water away from potential entry points
    * Drainage – providing means of removing water that does enter.
    * Drying – allowing any remaining moisture to be removed by ventilation or diffusion.
    * Durability – providing materials with appropriate durability.
After considering the ease of application of these four principles, a new set of principles were arrived at, with the goal of making the new ones easier to remember and apply 'on site'.
 
After publishing the "Six Principles of Weathertightness', BEAL asked several builders to apply the new principles to building situations that they were facing. Each builder found the new principles easy to remember and easy to apply when facing a situation that required a small but essential redesign of the exterior wall. e.g. adding a small roof over a back door.
 
Over the years the Six Principles of Weathertightness have been applied to many complex and simple wall designs and found to be reliable in demonstrating what needed to be taken into account when designing a cladding or wall or roof plan.
 
The Six Principles of Weathertightness are -
  1. Buildings shall have a primary and secondary drainage plane
  2. The second drainage plane must be waterproof and drain to the outside
  3. The moisture that gets past the primary drainage plane must be managed properly
  4. Roofs and soffits, and decks acting as roofs, must drain separately to any walls
  5. The design of openings and penetrations in roofs and walls must also account for wind and capillary action
  6. Materials ought be durable for at least 25 years (except decorative paints)

Posted: Fri 21 Aug 2009

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