Diagram — what is being calculated
01 / Inputs
Zone multipliers (BRANZ/NZS 3604): Table 10.1 gives base values for Extra High wind zone. For Medium and Low wind zones, multiply by 1.3; for High wind zone, multiply by 1.1. Continuous rafter spans may be increased by 10% per Note 1.
02 / Result
Enter your required span and press Check Rafter Span
All rafter sizes at entered spacing
| Size (depth×thickness) | Wind Zone | Max Span | Adequate? |
|---|
NZS 3604:2011 — scope and limitations. Table 10.1 applies to ordinary rafters in timber-framed buildings within NZS 3604 scope. Valley rafters and hip rafters require different treatment — refer to NZS 3604:2011 Section 10. Ridge beams are not covered by Table 10.1 and require specific design. Buildings with rafter spans exceeding these tables or outside NZS 3604 scope require engineering design. All results must be verified by a Chartered Professional Engineer or Licensed Building Practitioner.
NZS 3604:2011 Table 10.1 — Rafter Maximum Clear Span (mm), Extra High Wind Zone, Light Roof
Multiply by 1.3 (low/medium) or 1.1 (high) for other zones. Add 10% for continuous over 2+ supports. Source: NZS 3604:2011 Table 10.1, BRANZ Guideline.
| Size (mm) | @ 400c | @ 600c | @ 900c | @ 1200c |
|---|---|---|---|---|
| 90×45 | 2350 / 2550 | 2050 / 2200 | 1700 / 1800 | 1500 / 1600 |
| 140×45 | 3800 / 4100 | 3300 / 3600 | 2700 / 2950 | 2400 / 2650 |
| 190×45 | 5100 / 5500 | 4450 / 4800 | 3650 / 3950 | 3250 / 3500 |
| 240×45 | 6400 / 6900 | 5600 / 6000 | 4550 / 4950 | 4100 / 4400 |
| 290×45 | 7700 / 8300 | 6700 / 7250 | 5500 / 5950 | 4900 / 5300 |
Values shown as SG8 / SG10. Heavy roof spans are approximately 15–20% less.