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Roof Sheathing Calculator

Boards by sheet, battens by metre, nails by spacing - all three at once.

Quick answer

With the default inputs: Sloped roof area 115.5 m² · Board width 1.22 m · Board length 2.44 m etc.Boards incl. waste 43 sheets

Use your own dimensions ↓

Inputs

m²
%

Result

Boards incl. waste
43sheets
Area per board2.977m²
Boards net39sheets
Batten length340m
Sheathing nails5133pcs
Batten nails1019pcs
Total nails6152pcs
How this is worked out

Sheathing is the board layer under the tiles; it carries the covering, spreads the load and gives the battens something to fix to. Board count is sloped area divided by board area, rounded up, plus waste. Roof waste runs much higher than wall waste because boards are laid diagonally and cut at ridges, eaves, valleys and dormers - 8% is the baseline, rising to 12-15% on complex multi-pitch roofs with dormers. Battens are estimated as sloped area divided by spacing: at 340 mm that is about 2.9 m per m². Batten spacing must match the effective tile length (tile length minus head lap); wider than that and the tiles will not hang, narrower wastes material and money. Nails are estimated at 150 mm centres on the board face plus three per metre of batten, and should be tightened up around edges - board edges and ends must land on a rafter or the nails have nothing to hold. This tool covers timber decking only; purlins on steel roofs are separate.

Next up: Roof Tile Calculator · Roof Flashing Calculator

Formula

Board areaa = width × length
Boards netn = ⌈As / a⌉
With wasteN = ⌈n × (1 + waste)⌉
Batten lengthL = As / batten spacing
Board nailsn = As / spacing²
Batten nailsnb = L × 3
115.5 m² sloped, 1220×2440 mm boards, 8% waste, 340 mm batten spacing, 150 mm nail spacing: 2.977 m² per board, 39 boards net, 43 with waste, ~340 m of batten, ~5133 board nails plus ~1019 batten nails, about 6152 in total.

Basis

FAQ

Why is sheathing waste higher than wall waste?
Because boards are laid on the slope and there are far more cuts: at the ridge, at the eaves, at valleys where two planes meet, around dormers and at verge closures. Every cut wastes part of a board and the offcuts are rarely usable. Use 8% for a simple mono-pitch or gable roof, 12-15% for a hip roof or one with dormers, and up to 20% for very complex shapes. Order a couple spare - a second delivery means waiting, plus batch and colour differences.
How is batten spacing set?
By the effective tile length, not by habit. A 420 mm tile with an 80 mm head lap has a 340 mm effective length, so the battens must be at 340 mm: wider and the tiles are not held and will lift in wind, narrower and you waste material and add cost. The first batten at the eaves is set from the tile overhang (normally 50 mm) or the first course will not line up with the rest. The top batten at the ridge is set separately so the ridge tiles lap evenly on both sides.

Cite this page

Use this format in reports, method statements or coursework. The link is permanent.

Building Calculator. Roof Sheathing Calculator. 2026-10-25. https://jianzhujisuan.com/en/roof-sheathing

Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.