Hip Roof Calculator (Australia)
Free hip roof calculator for Australia. Compute roof area in m², rafter and hip rafter lengths, and ridge length for any equal-pitch hip roof — to AS 1684 and AS 2050.
Hip Roof Calculator
How this hip roof calculator works for Australian projects
Enter the building length, width, eave overhang, and pitch (in degrees by default). The calculator returns the roof surface area in m², the common rafter length, the hip rafter length, the ridge length, and the equivalent in roofing squares for reference.
The hip is the dominant roof shape on Australian project homes — it sits cleanly on a rectangular plan, sheds wind on all four sides (important in cyclone country), and gives generous eaves for shading. AS 2050 (slate and tile installation), AS 1562.1 (sheet roofing), and AS 1684 (timber framing) together govern the structural and waterproofing detail.
The math, derived
Slope factor:
slope factor = 1 / cos(pitch in degrees)For typical Aussie pitches: 15° = 1.035, 22.5° = 1.082, 25° = 1.103, 30° = 1.155.
Surface area
roof area (m²) = (length + 2·overhang) × (width + 2·overhang) × slope factorFor an equal-pitch hip on a rectangular footprint, the four planes (two trapezoids + two triangles) sum to exactly the same total as a gable — the geometry collapses neatly into footprint × slope factor.
Rafters
common rafter = (width/2) × slope factor
hip rafter = (width/2) × √(2 + tan²θ)Hip rafters run diagonally from each corner to the ridge end and are typically 30–45% longer than commons. AS 1684.2 provides the rafter span tables for the rafter section needed at the calculated length.
Ridge
ridge length = length − widthThe overhangs cancel. A 12 m × 9 m footprint produces a 3 m ridge regardless of eaves overhang. On a square plan the ridge collapses to a point — a pyramid hip, common on heritage Federation homes.
Australian pricing context (2026)
From recent Master Builders Australia, Australian Roofing Contractors, hipages, and BlueScope/Lysaght quotes:
| Covering | A$ / m² installed | Typical pitch |
|---|---|---|
| Concrete tile (Boral, Monier) | A$70–A$110 | 17.5°+ |
| Terracotta tile (Bristile, Wienerberger) | A$120–A$180 | 22.5°+ |
| Colorbond Trimdek (BlueScope) | A$95–A$140 | 5°+ |
| Klip-Lok 406 / 700 (Lysaght) | A$130–A$190 | 2°+ |
| Standing-seam zinc / aluminium | A$220–A$320 | 5°+ |
| Slate (natural, imported) | A$260–A$420 | 25°+ |
A 180 m² Colorbond Trimdek hip in Sydney at A$120/m² installed is roughly A$21,600 for the covering, plus A$2,500–A$4,500 for scaffolding (HSE-compliant edge protection), A$600–A$1,000 for skip hire, and A$800–A$1,500 for hip cap, ridge cap, and barge flashing. Bushfire BAL-29 or BAL-40 zones add A$400–A$1,200 for ember-protected vents and gutter guard.
Common Australian mistakes
Mixing N-rated and C-rated framing. AS 1684.3 splits Australia into wind classifications N1–N6 (non-cyclonic) and C1–C4 (cyclonic). A hip roof framed to N3 detail in a C2 zone will fail engineer sign-off. Confirm wind classification from your local council or BOM regional wind speed map before sizing rafters.
Forgetting the BAL eaves detail. AS 3959:2018 (construction in bushfire-prone areas) requires non-combustible eaves linings and ember-protected vents in BAL-29 and above. Hip eaves wrap continuously around the building, so the spec applies to every metre of soffit — easy to under-quote.
Skipping anti-ponding boards. AS 2050 requires anti-ponding boards on all hip valleys and pitches under 22°. Concrete tile suppliers (Boral, Monier) refuse warranty on roofs without them. Allow 1 board per linear metre of hip.
Under-ordering hip and ridge cap. Hip cap goes down all four hip lines plus the ridge. Total cap material = 4 × hip rafter length + ridge length. On a 12 × 9 hip with 30° pitch that is roughly 4 × 5.85 + 3 = 26.4 m of cap — typically 9–10 cap tiles or 26 m of metal hip flashing.
Standards and references
- AS 1684.2 / 1684.3 — Residential timber-framed construction (non-cyclonic / cyclonic).
- AS 2050:2018 — Installation of roof tiles.
- AS 1562.1:2018 — Design and installation of sheet roof and wall cladding (metal).
- AS 3959:2018 — Construction of buildings in bushfire-prone areas.
- AS/NZS 1170.2 — Wind loading.
- NCC 2022 Volume Two — Class 1 and 10 buildings (residential).
Using this with the rest of the project
Once you have the m², size the framing with the roof truss calculator, price the covering with the roof cost calculator, and confirm the pitch against your chosen covering’s AS 2050 / AS 1562.1 minimum with the roof pitch calculator. For a side-by-side with a gable on the same plan, run both through the roof area calculator — the m² is identical, the cost difference comes from hip cap labour, anti-ponding detail, and 2–4% extra waste.
The hip is the default Aussie project-home roof. Get the geometry right at this stage and the Colorbond order, the truss schedule, the bushfire detail, and the engineer’s wind-rating sign-off all fall into a clean, defensible package.