About this calculator
This calculator takes off the tiling battens and counter-battens laid over the rafters: how many batten rows each slope needs at the covering's gauge, the total batten length, how many stock lengths that really is once the rows are packed into them, the counter-battens (one per rafter), and the timber volume.
The batten gauge is the covering manufacturer's figure, not this calculator's. The spacing between batten rows is set by the tile's length and the headlap the maker requires at your pitch, or by a sheet profile's module. The calculator offers a placeholder per covering type so it can produce a number before you have the real one, and warns when the gauge you enter falls outside a plausible band — but the placeholder is trade practice, not a standard and not a recommendation. Enter the figure from the fixing instructions; the calculator flags every result computed on the placeholder.
Stock lengths are packed, not divided. A 4 m batten cannot supply two 2.5 m rows; the calculator lays every row into stock lengths piece by piece, so the count you get is the count you buy.
Batten and counter-batten sections are your inputs. They size the timber volume and nothing else; this calculator does not check whether a batten can span your rafter spacing under a tiler's weight. National codes (BS 5534 in the UK, for example) do that, and this page does not.
Formula
gauge (max) = manufacturer's batten spacing, or the covering's placeholder
rows per slope = ceil(slope length / gauge) + 1
gauge used = slope length / (rows − 1) (≤ gauge max)
batten runs = rows per slope × slopes, each slope width long
batten net length = runs × slope width
stock lengths = first-fit-decreasing packing of every run (split at stock length)
+ the waste allowance as further pieces
purchased length = stock lengths × stock length
offcut = purchased − net
counter-battens = (ceil(slope width / rafter spacing) + 1) per slope, each slope length long
packed into stock lengths the same way
timber volume = purchased length × width × thickness (battens + counter-battens)
Rows: one batten at the eaves and one every gauge up to the ridge, the last interval rounded up into a whole extra row, so the gauge actually used is never more than the maximum. The eaves batten's exact position (set by the tile's overhang into the gutter) and the top batten's (set by the ridge detail) are not modelled — they shift the rows, not their number.
Area mode: give the roof surface area (not the plan area — see the roof
calculators) and the slope length, and the calculator treats it as one slope
area / slope length wide.
Worked example
Defaults: two slopes 5.5 m long and 10.6 m wide (the gable-roof calculator's default roof), concrete tile at the 340 mm placeholder gauge, 50 × 32 battens in 4 m lengths, 5 % waste, 50 × 25 counter-battens on rafters at 600 mm.
rows per slope = ceil(5500 / 340) + 1 = 17 + 1 = 18; gauge used = 5500 / 17 = 323.5 mm
batten runs = 18 × 2 = 36 runs of 10.6 m = 381.6 m net
packing each 10.6 m run = 4 + 4 + 2.6 m
72 × 4 m pieces fill 72 lengths
36 × 2.6 m pieces: two never fit one 4 m length -> 36 lengths = 108 net
waste 5 % = 19.08 m = 4 × 4 m + 3.08 m -> 5 more lengths = 113 to buy
purchased = 113 × 4 = 452 m; offcut = 452 − 381.6 = 70.4 m
counter-battens = ceil(10 600 / 600) + 1 = 19 per slope -> 38 × 5.5 m = 209 m net
packing each 5.5 m = 4 + 1.5; 38 × 4 m -> 38 lengths; 38 × 1.5 m pair up -> 19 = 57 net
waste 5 % -> 60 to buy = 240 m
timber (purchased) = 452 × 0.05 × 0.032 + 240 × 0.05 × 0.025 = 0.723 + 0.300 = 1.023 m³
Dividing 381.6 m by 4 m would say 96 battens. The packed count is 108 before waste — twelve more, because every 2.6 m remainder needs its own length.
FAQ
Where does the batten gauge come from? From the covering manufacturer's fixing instructions for that product at your pitch: tile length minus the minimum headlap, or the sheet's module. The defaults here (concrete tile 340 mm, interlocking clay tile 350 mm, tile-effect steel sheet 350 mm) are placeholders from trade practice so the page works before you have the figure. They are not standards; use the maker's number.
I have plain (double-lap) clay tiles. Why does the calculator warn? The clay option's plausible band (250–400 mm) is for interlocking tiles. Plain tiles gauge around 100 mm (a 265 mm tile at 65 mm lap, laid double). Enter the manufacturer's gauge; the warning says the figure is outside the band, and the rows are still counted.
Bitumen shingles — why no battens? Shingles are nailed to a continuous deck (boarding or OSB), not to spaced battens. For that covering the calculator reports the deck area to buy instead of batten rows, and still counts the counter-battens that ventilate the deck.
Why is the stock count higher than length divided by stock length? Because a batten row is a continuous piece between joints and a joint must land on a rafter — the leftover from one length cannot become part of a row it is too short for. The calculator packs actual pieces into actual lengths; division would send you to the yard twice.
What are counter-battens for and how are they counted? They run up each rafter under the tiling battens, holding the underlay clear and giving a ventilation and drainage gap. One per rafter: a rafter at each edge of the slope plus one per spacing, rounded up — the same count the roof calculators use.
Does the calculator check the batten size? No. The section only sizes the timber volume. Batten size for a given rafter spacing is a national-code matter (BS 5534 in the UK sets minimum sections by rafter centres); this page does not implement it.
Assumptions and limits
No standard is cited. Counting rows and packing lengths is arithmetic; the gauge is the manufacturer's. No standard governing this take-off was verified, so none is named. BS 5534 is mentioned only as the kind of document that sizes battens; this calculator does not apply it.
Placeholder gauges are trade practice, chosen so each covering produces a number before the real gauge is known, and every result computed on one is flagged. The plausibility bands (concrete 280–360, interlocking clay 250–400, metal sheet 250–600 mm) exist only to warn; they are not limits.
Rows are counted at a uniform gauge from eaves to ridge. The eaves batten's tile-overhang setback, the top batten's ridge setback, hips, valleys, abutments and any batten cut around a penetration are not modelled.
Packing assumes joints anywhere on a rafter and offcuts reusable in any row they fit; it does not require joints to be staggered.
Counter-battens are one per rafter, full slope length, packed the same way; the same stock length serves both.
Area mode is an approximation: one slope area / slope length wide. Use
slope mode when the roof has more than one slope of a known width.
No structural design. Batten and counter-batten sections are user inputs used solely for the timber volume.