Cladding and purlin takeoff

Roof sheets, wall sheets, purlin rows and net area — from dimensions you already have

Preliminary takeoff · not a quotation

An engineering calculator and an unfolded portal frame drawing side by side on a dark workbench

Design by Johnny Export engineer at Hebei Hongji Shunda, writing on steel buildings for Africa and South America.

Building and sheet data

Clear span m

Building length m

Eave height m

Roof pitch degrees

Openings to deduct m²

Sheet effective cover width m · yours

Purlin spacing m

Sheet end lap m

These are example values, not a recommendation. 24 × 60 m building, 8 m eave, 10° pitch, 24 m² of openings, 1.000 m cover width, 1.5 m purlin spacing, 0.20 m end lap. Type over every one of them with your own figures — especially the cover width, which is specific to the sheet profile you buy.

The one input we will not guess

Effective cover width is the distance one sheet actually covers after the side lap — not the flat width before forming. It changes with profile and thickness.
Read it from the sheet supplier's data for the profile you are buying. Two profiles of the same nominal width can cover differently.
If you order against a guessed figure, you either buy short or you buy waste. This page will not fill that number in for you.

Takeoff

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sheets, roof and wall together

Net cladding area

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Purlin rows

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Purlin total length

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Line	Value	How it comes out

Send the span, the length and the sheet profile. We confirm the takeoff against the actual layout.

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What this takeoff leaves out

Ridge, eave, corner and opening flashings; fixings, sealant and closure strips.
Wall girts and any secondary steel other than roof purlins.
Sheet thickness, coating and profile — quantities here do not depend on them.
Sheet layout at hips, valleys and curved work. The figure is a straight-run takeoff; the shop drawing governs.

How these numbers are worked out

Everything below is arithmetic on the eight inputs. Nothing is drawn from a table of typical values, so you can rework any line by hand or in a spreadsheet.

Areas

roof slope length = (clear span ÷ 2) ÷ cos(pitch)
roof area = 2 × roof slope length × building length
wall area = 2 × (clear span + building length) × eave height
net area = roof area + wall area − openings

Sheets

sheet run (m) = net area ÷ effective cover width × 1.05
roof pieces = 2 × building length ÷ effective cover width, rounded up, then × 1.05
wall pieces = perimeter ÷ effective cover width, rounded up, then × 1.05
roof piece length = roof slope length + end lap
wall piece length = eave height

Purlins

purlin rows per slope = roof slope length ÷ purlin spacing + 1
purlin rows total = 2 × rows per slope
purlin length = rows total × building length

Why the roof area is larger than the floor. On a gable with the ridge at mid-span, each slope is span ÷ 2 ÷ cos(pitch) long, so the sloped surface is always longer than the plan width. A 10° pitch adds about 1.5%.
Why sheets are counted per surface, not from the area alone. A roof sheet runs up the slope and a wall sheet runs up the eave, so the two surfaces are counted separately and each is rounded up. That is why the piece count lands slightly above the area ÷ cover width check shown in the table.
Where the 1.05 comes from. Five per cent cutting and lapping allowance on every run. It is an allowance, not a measurement — on a building with many openings or a short run, the real waste is often higher.
Why the purlin count adds one. A run of roof slope length ÷ purlin spacing spaces needs one more purlin than spaces: the first sits at the eave, the last at the ridge.
What governs in the end. Your shop drawing. This page exists so you can size a budget and a delivery before that drawing exists, not so you can order from it.

Ready to check it against a real layout

Send the eight numbers above plus the sheet profile you intend to buy.
We return the takeoff with flashings and fixings counted, and flag anything the straight-run method misses.

Quantities only. This page carries no price, no lead time and no commitment — those follow a drawing. Last reviewed 2026-10-29.