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Cut roof calculator: timber for a traditional pitched roof
Estimate the rafters, ceiling joists, straps and fixings for a traditional cut roof, from simple gables to hipped and valley roofs.
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How the calculation works
A cut roof is built on site from loose timber. The calculator works out rafter lengths from the span, pitch and overhang, counts rafters and ceiling joists from the roof length and spacing, and adds collars, purlins, trimmers, straps and fixings as selected.
Hipped and valley roofs need extra hip, valley and jack rafters, which the calculator allows for when you choose the roof type.
Cut roof or trusses?
Cut roofs suit awkward shapes, extensions and rooms in the roof. Trussed rafters are factory made, quicker to fit and usually cheaper on simple spans, but leave less usable loft space.
Timber sizes for a cut roof should follow the structural design.
Worked example
An 8 m long, 6 m wide duo pitch roof with gable ends, 150 mm rafters at 400 mm centres:
| Material | Quantity | Price (ex VAT) |
|---|---|---|
| 47mm x 100mm x 4.8m Treated C24 Regularised Kiln Dried Sawn Timber (4 x 2) | 4 | £51.68 |
| 47mm x 175mm x 4.8m Treated C24 Regularised Kiln Dried Sawn Timber (7 x 2) | 2 | £61.98 |
| Heavy Duty Engineered Bent Strap 1000mm | 10 | £72.30 |
| Heavy Duty Engineered Bent Strap 1500mm | 20 | £107.80 |
| Paslode Galvanised-Plus IM360 Collated Nails 3.1mm x 90mm 1100 Pack | 1 | £78.60 |
| ForgeFix Multi-Purpose Screw 4.0 x 50mm ZYP Qty 200 | 2 | £7.30 |
| Materials total | £379.66 | |
Today's prices, excluding VAT and delivery. Labour, plant hire and some items are priced when you request a quote. Use the calculator above for your own measurements.
Frequently asked questions
What is a cut roof?
A roof framed on site from individual rafters, joists and purlins, rather than from factory-made trusses.
Is a cut roof more expensive than trusses?
Often, because it takes more labour on site. It is chosen for complex shapes or where usable loft space matters.
Does this include the roof covering?
No, it covers the structure. Use the roofing calculator for tiles, battens, membrane and ridge.