Learning from the mistakes of the past

Weathertightness is not only an issue for New Zealand’s existing housing stock.

Nick Gaites, director of Reveal Building Consultants and an executive member of NZIBS, says many builders concerned about “risky” designs for new homes they are being contracted to build, are turning to Registered Building Surveyors for advice.

“We are seeing an increase in the number of complex designs which makes them more difficult to construct. When a contractor takes on a job they really need to do a thorough review of the design from a practicality point of view.  They need to ask themselves if the building will be fit for purpose.  They need to have an appreciation of whether or not it is a risky design, that is likely to compromise weathertightness.”

He says most Registered Building Surveyors have the necessary skills to carry out design peer review.

“A lot of what we see is not catastrophically bad. However, we can point out where the designer has used rather high-risk details and materials that aren’t necessarily the easiest to install. The other thing we see is a lack of information, with certain critical dimensions missing from the design details, and even missing fixings for the claddings and building components. It often gets left up to the builder to make these decisions on site which adds to their liability.”

Nick says once a design has been approved by the Council for Building Code compliance, it is critical builders don’t deviate from it in terms of detailing or materials selection.

“We have had situations where builders might have affinities with certain products and may substitute them into the build, which can compromise weathertightness or another structural aspect of the building due to material incompatibility. It is very important a set process is undertaken, which is to start with a good design, complete a design review, and implement the design using the materials and details provided by it.”

He says one of the most important detail to get right is to ensure flashings discharge water to the outside of the cladding rather than to the drainage cavity.

It’s also important to minimise horizontal surfaces, ensure claddings are kept clear of the ground base, and treat membranes of enclosed balconies over habitable spaces with extreme caution.

“It is critical the mistakes of the past are not repeated.”

Builders can also sign up for a series of 101 courses on weathertightness run by NZIBS, says Nick.

“It’s a great way for builders to upskill earn LBP points and gives them more confidence around design checks, and making decisions about whether or not it is prudent to proceed with a high-risk design.”