Brick veneer cavity: the wall is a screen, not a barrier

How the 50mm cavity, weep holes and flashings behind a brick veneer actually keep a NZ wall dry.

Brick veneer is a single skin of masonry standing in front of the real structural wall, separated by a 50 mm drainage cavity. The crucial thing to understand is that the veneer is a screen, not a barrier — wind-driven rain soaks straight through brick and mortar. Weathertightness comes from the cavity, the flashings and the weep holes that drain that water back out, not from the brick itself.

NZS 4210 and E2/AS1 §9.2 govern masonry veneer.

Critical specs

Cavity: 50 mm minimum (BRANZ and NZS 4210, even though E2/AS1 allows 40–70 mm).
Brick ties: a 600 × 400 mm grid (every 4th course on a 600 mm stud). Use SS316 ties on the coast; galvanised in Zone A/B.
Top venting: a 10 mm gap to the soffit, or omit the mortar in every 3rd perpend of the top course.
Weep holes: every 3rd perpend at the base, and below every window.
Mortar joints: concave (ironed), weatherstruck, or struck-flush — tooled off for density.

Keeping the cavity clean

The most common veneer failure is blocked weep holes or mortar bridging the cavity. Droppings pile up at the base, span the gap and wick water across to the frame. A clean cavity and open weeps are what make the system work.

Mortar droppings: use a mortar board in the cavity to catch them.
Clean-out: leave removable bricks every 3rd–4th brick in the bottom course so the base can be cleared.

Getting the base and openings right

Foundation step: the cavity bottom sits a minimum of 50 mm below floor level, and the foundation rebate must be waterproofed.
Openings: jamb flashings overlap sill flashings at openings.

Plain-English guide, not advice. This page helps you understand and navigate the rules — it is general information, not design, engineering or consent advice, and it does not reproduce the copyrighted tables of NZS 3604 or any Standard. Always check the current Standard or Acceptable Solution and your BCA, and use a suitably qualified LBP, engineer or QS where it matters.

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Common questions

How wide should a brick veneer cavity be?

BRANZ and NZS 4210 call for a 50 mm minimum drainage cavity, even though E2/AS1 allows a range of 40–70 mm. The cavity is what drains wind-driven rain back out, so it does the weathertight work — not the brick itself.

Where do the weep holes go?

Weep holes go in every 3rd perpend along the base of the veneer, and below every window. They let water that gets past the brick drain back out of the cavity, so keeping them open is critical.

Why do brick veneer walls leak?

The most common veneer failure is blocked weep holes or mortar bridging the cavity. Mortar droppings pile up at the base, span the gap and wick water across to the frame. A mortar board in the cavity plus removable clean-out bricks every 3rd–4th brick in the bottom course keep it clear.

Which brick ties should I use near the coast?

Use SS316 stainless ties in coastal conditions, and galvanised ties in Zone A/B. Ties are set out on a 600 × 400 mm grid, which works out to every 4th course on a 600 mm stud.

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