"What is a trussed roof?"

"A trussed roof uses prefabricated triangular timber frames (trusses) made off site to a structural design, then craned or lifted into position and fixed at regular centres. Fink (W) trusses are the most common type for UK houses."

"How many roof trusses do I need?"

"Divide the building length by the truss spacing and add one. Trusses are usually fixed at 600mm centres, so a 10m long building needs (10 ÷ 0.6) + 1 = approximately 18 trusses. Always confirm spacing with the truss designer."

"What spacing are roof trusses fixed at?"

"600mm centres is standard for domestic trussed roofs in the UK, though 400mm is sometimes used for heavier coverings or higher loads. The spacing is set by the truss design and the roof covering weight."

Trussed Roof Calculator UK | Roof Truss Quantities & Materials

Calculate the number of roof trusses, bracing, battens and covering from your span, pitch and building length. Free UK construction calculator.

Results are estimates only and may vary depending on site conditions, material specifications and waste. EasyEstimate and its affiliates accept no responsibility for any loss or damage arising from reliance on these figures. Always verify quantities with your supplier before ordering.

How to Calculate a Trussed Roof

A trussed roof is built from prefabricated frames fixed at regular centres. Estimating it means counting the trusses, then adding bracing, wall plates, battens and the roof covering.

The Formula

Number of trusses = (building length ÷ truss spacing) + 1
Roof area = rafter length × building length × 2 (for a duo-pitch roof)
Bracing = longitudinal, diagonal and chevron bracing per BS 5268 / truss design
Covering = roof area × coverage rate (tiles, battens, felt) + waste

Worked Example: 8m span, 30° pitch, 10m long

Trusses at 600mm centres = (10 ÷ 0.6) + 1 = 18 trusses
Rafter length = (8 ÷ 2) ÷ cos(30°) = 4 ÷ 0.866 = 4.62m per side
Roof area = 4.62 × 10 × 2 = 92.4 m²

Enter your span, pitch and length in the calculator above for truss counts, bracing, covering and a waste allowance.

Mono Pitch Roof Calculator — single-slope lean-to roofs
Hand Cut Roof Calculator — traditional on-site cut roofs
Roofing Calculator — tiles, battens and felt for any roof

Frequently Asked Questions

What is a trussed roof?: A trussed roof uses prefabricated triangular timber frames (trusses) made off site to a structural design, then craned or lifted into position and fixed at regular centres. Fink (W) trusses are the most common type for UK houses.
How many roof trusses do I need?: Divide the building length by the truss spacing and add one. Trusses are usually fixed at 600mm centres, so a 10m long building needs (10 ÷ 0.6) + 1 = approximately 18 trusses. Always confirm spacing with the truss designer.
What spacing are roof trusses fixed at?: 600mm centres is standard for domestic trussed roofs in the UK, though 400mm is sometimes used for heavier coverings or higher loads. The spacing is set by the truss design and the roof covering weight.

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