BRANZ research findings: what actually works

The standards tell you the minimum; BRANZ research tells you what actually works. BRANZ (the Building Research Association of NZ) tests real assemblies and publishes findings that explain the why behind the rules and fill the gaps prescriptive standards leave. The findings below — drawn from BRANZ Build magazine, Bulletins, Good Practice Guides, the House Insulation Guide and Appraisals — are research-backed guidance worth knowing on top of the code.

Dwangs & nogs make a negligible structural contribution

Standard practice is 90×45 SG8 dwangs at 800mm vertical spacing, but the science is settled: more insulation and less timber framing gives better thermal and acoustic performance. Source: BRANZ Build — ‘Dwangs – moving with the times’ (2020), and BRANZ Studies 1991, 1998 and 2011.

• Dwangs do not contribute meaningfully to wall racking resistance, lined or unlined.
• Dwangs are not required to support studs laterally for any single-storey situation where horizontal sheet or board lining is used (NZS 3604:2011 cl 8.5.4).
• For edge support of linings, dwangs provide little benefit at studs at 480mm centres or closer.
• They’re required only where the cladding needs intermediate fixing — for example, vertical profiled metal at 400–480mm.
• Alternative: use 45×45 batten dwangs instead of full 90×45 to reduce thermal bridging while still satisfying lateral support.

Wall framing ratios are higher than the H1 default assumes

When all the timber is counted, real walls carry more framing than the H1 schedule method credits — and more framing means more thermal bridging and a lower actual construction R-value. Source: BRANZ + Beacon Pathway 2020 study (ER53).

• Actual wall timber framing fractions run 24–57%, averaging 34%, when all timber is counted.
• The H1/AS1 schedule method only counts studs, full-depth dwangs, and top and bottom plates.
• The default minimum framing fraction under H1/AS1 6th edition is 38% for walls.
• A higher framing ratio means more thermal bridging and a lower actual construction R-value.

To genuinely hit an R2.0 construction value, consider 90mm framing plus a 45mm internal services cavity. The Healthy Home study found that 90mm dwang-free framing with a 45mm insulated services cavity is $11/m² cheaper than 140mm framing — and thermally better.

B1/AS1 Amendment 11 — wall footings need 2× D12 bars

An update to the BRANZ House Building Guide (3rd ed) reflects B1/AS1 Amendment 11 for foundation walls built per NZS 3604:2011 §7.

• Foundation walls now require 2× D12 reinforcing bars in the wall footing.
• The single D12 bar option has been deleted — Figures 7.13(A), 7.14(A), 7.15(A) and 7.16(A) have been removed.
• 30mm cover is required.
• Slab reinforcing must be tied to the foundation reinforcing per the NZS 3604 figures.

Slab reinforcing — current BRANZ minimums

These are the current BRANZ minimums for slab mesh. Source: BRANZ Build — ‘Concrete slabs and control joints’, and NZS 3604 §7.5.

• 500E reinforcing mesh (SE62), minimum 2.27 kg/m² — that’s 1.15 kg/m² each direction.
• Sheet lap: 225mm minimum, or per the manufacturer.
• Mesh extends to within 75mm of the slab edge.