Key points at a glance
- Building Code clause E2 (External Moisture) requires buildings to keep water out.
- Poor weathertightness caused New Zealand’s costly “leaky building” crisis.
- Correct flashings, cavities, junctions and cladding detailing are essential.
- Weathertightness work is Restricted Building Work and generally needs an LBP.
What the Code requires
Clause E2 of the Building Code requires that buildings are constructed to prevent external moisture causing undue dampness, damage to building elements, or harm to occupants. This covers roofs, walls, windows, decks and the many junctions where water can get in.
Modern detailing often uses a drained and vented cavity behind cladding, correct flashings, and careful sequencing so that any water that gets past the cladding can drain and dry.
Avoiding leaky-building problems
Weathertightness failures can be extremely expensive to remedy because damage is often hidden until framing has rotted. Getting design details right, using compliant products, and following the manufacturer’s installation instructions are the best protection.
Because it affects weathertightness, external cladding work on homes is Restricted Building Work and must generally be carried out or supervised by a Licensed Building Practitioner.
For homeowners
- Insist on correct flashings and cavity systems — do not cut corners on detailing.
- Keep producer statements and product certificates for cladding work.
- Get regular maintenance checks around windows, decks and roof junctions.
For tradespeople
- Follow manufacturer specifications and E2 Acceptable Solutions precisely.
- Document cavity, flashing and junction details for the consent and CCC.
- Ensure external moisture work is done or supervised by an LBP.
Official sources
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