01 / Deck Geometry
Distance from finished ground to top of pile (= bearer bottom). Not the deck surface.
Backspan must be ≥ 4 × cantilever (NZS 3604 cl. 6.10).
02 / Location & Exposure
Key NZS 3604:2011 / BRANZ rules:
• Pile top (= bearer bottom) min. 150 mm above ground (cl. 6.4.1.1)
• Bearer cantilever ≤ 0.25 × adjacent span (cl. 6.10) — backspan ≥ 4 × cantilever
• Cantilevered deck joists: backspan ≥ 1.5 × cantilever
• Cantilevered balcony joists: total length ≥ 2.25 × cantilever
• Decking weight ≤ 40 kg/m²; balustrade ≤ 26 kg/m²
• H3.2 above ground; H5 piles/posts in ground (NZS 3602)
• Pile top (= bearer bottom) min. 150 mm above ground (cl. 6.4.1.1)
• Bearer cantilever ≤ 0.25 × adjacent span (cl. 6.10) — backspan ≥ 4 × cantilever
• Cantilevered deck joists: backspan ≥ 1.5 × cantilever
• Cantilevered balcony joists: total length ≥ 2.25 × cantilever
• Decking weight ≤ 40 kg/m²; balustrade ≤ 26 kg/m²
• H3.2 above ground; H5 piles/posts in ground (NZS 3602)
03 / Compliance Checks
Enter deck dimensions to run compliance checks
Scope and limitations. This tool applies NZS 3604:2011 and BRANZ BU560 rules for timber decks within NZS 3604 scope (residential, ≤ 10 m wall height, ≤ 2 storeys, on good ground). Cantilevered joists supporting external braced walls require specific engineering design. For pile design on poor ground, sloping sites, or buildings outside NZS 3604 scope, engage a Chartered Professional Engineer.
Deck Construction Quick Reference
| Parameter | Requirement | Source |
|---|---|---|
| Min. pile top above ground | 150 mm | NZS 3604 cl. 6.4.1.1 |
| Min. bearer bottom above ground | 150 mm | BRANZ BU560 |
| Min. pile depth — gravel soil | 900 mm | NZS 3604 cl. 6.6 |
| Min. pile depth — other soil | 1200 mm | NZS 3604 cl. 6.6 |
| Anchor pile embedment | 900 mm + concrete | NZS 3604 cl. 6.6 |
| Max. pile height above ground (ordinary) | 3000 mm | NZS 3604 Table 6.7 |
| Max. pile height above ground (concrete) | 1500 mm | NZS 3604 Table 6.7 |
| Max. pile height above ground (driven timber) | 3000 mm (anchor: 600 mm) | NZS 3604 Table 6.7 |
| Min. deck joist depth for cantilever barrier | 190 mm | NZS 3604 Table 7.2 |
| Max. decking weight | 40 kg/m² | NZS 3604 cl. 7.1.5.1 |
| Max. balustrade weight | 26 kg/m² | NZS 3604 cl. 7.1.5.1 |
| Fixings Zone B/C | HDG or stainless steel | NZS 3604 cl. 6.8 |
| Fixings Zone D | Stainless steel only | BRANZ BU560 |
| Fixings with CuAz/AZQ timber | Stainless steel only | BRANZ |
| Timber treatment — deck above ground | H3.2 minimum | NZS 3602 / B2/AS1 |
| Timber treatment — piles in ground | H5 minimum | NZS 3602 / B2/AS1 |
| Timber treatment — deck boards | H3.2 minimum | NZS 3602 / B2/AS1 |