E2/AS1: Your ticket to building weathertight homes

 

 

It’s a well-known saying: all houses leak. That’s why Clause E2 of the New Zealand Building Code is a must-know for anyone in the trade.

At its core, E2 is designed to ensure buildings are as weathertight as possible, meaning rain and wind-driven water stay on the outside, where they belong. The rules apply to everything from claddings and flashings to junctions, windows, penetrations and decks, and roof types. However, it’s also about managing external moisture, so that when water does get in, it can also get out again without creating mould, rot and structural damage.  

While the clause itself sets out performance expectations, the most common way to meet them is with the Acceptable Solution: E2/AS1.

What’s E2/AS1?

E2/AS1 is essentially a “how-to” guide for compliance. It spells out tried-and-true building methods for achieving weathertightness in timber-framed buildings up to 10m high. The first part is around ensuring materials are appropriate for the project (and don’t clash with adjoining materials), then it goes into details and drawings of the common junctions and penetrations in roofs and walls, setting out the right cladding to use depending on a building’s weathertightness risk.  

Drawings of gutters, barges, fascia and soffits, parapets, decks and pergolas, even garage door thresholds – it’s all in here. 

It’s not a one-size-fits-all solution – it doesn’t apply to solid masonry, steel framing, bifold and sliding doors, buildings over three storeys or non-aluminium joinery. Any of these and other design elements not shown in E2/AS1 will require special design and signoff. 

As building consent authorities (BCAs) use E2/AS1 to assess whether specific designs or alternatives will comply with the Building Code, it is worth being across them. Getting familiar with the standards will save a lot of time and effort when it comes to applying for building consents, so you know when certain elements aren’t likely to get past the inspector.

Getting it wrong isn’t just about failing inspection – it can mean costly call-backs, repairs, or even full reclads. Following E2/AS1 means you’re sticking with proven methods that reduce the risk of moisture ingress and structural damage down the track.

And with more extreme weather events and tighter compliance rules, councils are paying closer attention to flashing details, junctions and material compatibility than ever before. E2 is not the place to wing it. 

All these details and a companion guide, which helps calculate the weathertightness risks of certain building designs, are available on the Department of Building and Housing Website here.