What is Building Code clause E2 weathertightness?
Short answer
E2 is the Building Code clause covering exterior weathertightness — keeping water out of buildings. It sets minimum standards for cladding, flashings, windows, and roof junctions. The Acceptable Solution E2/AS1 is the safe-harbour route most designs use; alternative solutions are possible but need extra documentation. E2 is the most-litigated clause in NZ — leaky-home claims pivot on it.
Key facts
- Sets standards for cladding, flashings, window/door junctions, roof penetrations
- Acceptable Solution E2/AS1 is the safe-harbour route
- Alternative solutions need engineer / designer sign-off
- Risk score (E2/AS1 Figure 8) determines cladding choice eligibility
- Most leaky-home cases pivot on E2 non-compliance
The risk score and why it matters
E2/AS1 calculates a 'risk score' based on wind zone, height, complexity, cladding type, and eaves. The higher the score, the more limited the cladding options.
A high-risk score house (no eaves, lots of corners, multi-storey, high wind) can't use direct-fixed monolithic cladding under E2/AS1 — it needs a drained cavity. Get this wrong at design and you'll fail consent or worse, build a leaky house.
Common E2 failures
Inadequate or missing head flashings above windows. Direct-fixed cladding on high-risk junctions without a cavity. Wrong sealants used at junctions. Roof flashings cut short. Penetrations not properly weather-sealed.
Most of these are visible on the finished build if you know what to look for — but only specialists do. Independent inspections during framing and pre-cladding are standard on careful builds.
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Related questions
Sources: Building Code clause E2; E2/AS1 Acceptable Solution. General information for NZ homeowners, not legal advice — building rules change and vary by council, so confirm critical details on the official source before acting. Last updated 2026-05.