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What timber do I need to build a shed?
A framed timber building end to end: base, floor, four walls, roof and covering. It is the old shed calc rebuilt — same 400 floor centres and 600 wall centres, now doing the arithmetic itself.
1
Measure it
Every box has its own unit next to it.
Change the unit beside any box and the number converts. The (i) beside each question says what the box wants and where the figure usually comes from. Anything marked per cent is a percentage of the quantity above it.
2
Check the rates
Rates and assumptions used
These are the figures the calculator works to. Change any of them and the order list updates — your merchant’s pack sizes and your own waste allowances beat the defaults every time.
Wall studs = each wall’s length ÷ 600 + 1, all four walls added up
Cladding = wall area ÷ cover width — cover width, not the board width
Apex roof slope = 2 × √((width ÷ 2)² + rise²)
The figures the calculator works to. Every one can be changed in step 2, and your merchant’s pack sizes and your own waste allowances beat these defaults every time.
Rate
Default
Why
Floor joist centres
400 mm
Wall stud centres
600 mm
Rafter centres
600 mm
Floor / roof sheet
2.88 m²
2400 × 1200.
Felt roll
10 m²
10 m × 1 m.
Felt laps
15 %
Breather membrane roll
30 m²
A worked example
With the defaults the page opens on:
How long is the shed? 3.6 metres
How wide is it? 2.4 metres
How tall at the eaves? 2.1 metres
Apex or pent roof? Apex — ridge down the middle
How much does the roof rise? 0.6 metres
Which cladding? Feather edge 150 mm — 125 cover
Spare for waste 10 per cent
Base & floor
Floor area: 8.64 m²
Bearers: 5 no. — across the width at 600 mm
Floor joists: 10 no.— at 400 mm centres
Joist timber: 24 m
Floor sheets 18 mm: 4 sheets
Walls
Wall area: 25.2 m² — perimeter 12 m × 2.1 m
Studs: 24 no.— all four walls at 600 mm centres
Stud timber: 50.4 m
Plates, top & bottom: 24 m
Noggins: 12 m — one row at mid height
Cladding: 221.76 m— cover width 125 mm, +10%
Breather membrane: 1 rolls
Roof
Slope length: 2.68 m — apex roof, 0.6 m rise
Roof area: 9.66 m² — slope × length
Rafters: 14 no.— at 600 mm centres
Rafter timber: 18.78 m
Roof sheets 11 mm OSB: 4 sheets
Roofing felt: 2 rolls— +15% laps
Fascia & barge: 14.68 m
Change any figure above and every line recalculates; the small print under each row is the sum that produced it.
Questions people ask
How much timber to build a shed?
The calculator gives the count and the total length for every part - floor joists at 400 mm centres, wall studs at 600 mm on all four walls, rafters, plates and noggins - from the length, width, eaves height and roof rise.
Why does cladding use cover width, not board width?
Because the lap is lost. A 150 mm feather-edge board covers 125 mm; ordering on 150 leaves you a sixth short. The cladding options carry their cover widths.
Apex or pent?
An apex roof sheds water both ways and has two slopes of rafters; a pent roof is one slope, simpler and cheaper. Pick one and the roof rows change.
Read before you order. These work out quantities, not structural design — spans, lintels, rebar and foundation depths need an engineer and Building Control sign-off. Waste allowances are defaults, not promises: awkward cuts, long runs and bad weather all eat more than 5%. Where a merchant sells whole packs, the figure is rounded up to whole packs.
