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E2/AS1 risk matrix: a worked example

Walk through how the E2/AS1 risk matrix scores a real elevation and what that score tells you about the compliance pathway.

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The E2/AS1 risk matrix scores each elevation of a building to work out which weathertightness pathway you have to follow. It isn’t a “score to pass” — it’s a score that determines the compliance pathway, so it’s worth understanding before you commit to a cladding fixing method.

The factors (E2/AS1 §3.4)

The matrix rates each elevation across a set of risk factors, each with its own range of points:

Worked example — Tauranga beachfront

Take a typical 2-storey beachfront house in Tauranga, scoring the north-facing front elevation. Here’s how each factor stacks up:

  1. Wind zone — Very High (coastal Tauranga): 1
  2. Storeys — 2 storeys: 1
  3. Roof/wall intersection — mono-pitch into vertical wall (medium complexity): 1
  4. Eaves width — 450mm eaves (medium-narrow): 4
  5. Envelope complexity — sloped wall + bay window + balcony: 3
  6. Deck design — cantilevered timber deck over upper-storey window: 6

Total score: 16.

Result: cavity construction mandatory

A score of 16 is well above threshold, so the front elevation MUST use cavity construction — direct-fix is not allowed for ANY cladding system. Sheathing is also required (Very High wind zone, E2/AS1 §9.4).

Specific implications for this elevation:

How to reduce the score

The score is worth thinking about at design stage. A few moves that pull it down:

The scoring matters most when you’re claiming direct-fix on a specific elevation, or pushing into the very-high risk envelope. Most modern NZ builds score above 6, so cavity is standard anyway.

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

What score triggers mandatory cavity construction in the worked example?

In the Tauranga beachfront example the front elevation scores 16, which is well above threshold. At that score cavity construction is mandatory and direct-fix is not allowed for any cladding system.

Which factors does the E2/AS1 risk matrix score?

Under E2/AS1 §3.4 the matrix scores wind zone (0–2), number of storeys (0–1), roof/wall intersection design (0–1), eaves width (0–5), envelope complexity (0–6) and deck design (0–6) for each elevation.

How can you reduce an elevation's risk score at design stage?

Options include wider eaves (600mm+ saves 1–2 points), a simpler eaves-to-eaves roof-wall junction (saves 1 point), covering the deck (loses the deck score entirely), removing sloped walls or bay windows (envelope −1 to −2), and swapping hidden internal gutters for an external gutter (deck −2).

Is the risk matrix a pass/fail test?

No. It isn't a score to pass — it's a score that determines the compliance pathway. Most modern NZ builds score above 6, so cavity is standard; the scoring matters most when claiming direct-fix on a specific elevation or pushing into the very-high risk envelope.

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