How-To · 10 min read
Roof Sheet Takeoff and Ordering: How to Measure and Buy Roofing
Ordering roofing is mostly arithmetic. This guide shows how to take off sheet quantities, allow for waste, and order matching fasteners, flashings and rainwater so nothing is missing on install day.
In short
A roof takeoff converts roof measurements into a materials list: number of sheets at each length, screws, flashings and gutters. The key numbers are the cover width of your profile, the slope length from eave to ridge, and a waste allowance of around 10 percent.
This guide walks through a worked example for a simple gable roof, lists the accessories people most often forget, and explains when to use cut-to-length versus standard stock lengths.
1. Understand cover width versus sheet width
Every profile has two widths: the actual sheet width, and the effective cover width once sheets overlap. Cover width is the number you use for takeoff because it is what each sheet actually covers on the roof. Corrugated, Trimdek and Spandek cover 762 mm; Klip-Lok 700 covers 700 mm. Always calculate with cover width, never sheet width, or you will order too few sheets.
2. Work out sheet length and count
For a simple gable roof, measure the slope length from the eave to the ridge along the rake, and add your eave overhang, usually 50 to 100 mm. That is your sheet length. Then measure the length of the roof along the eave and divide it by the cover width of your profile to get the number of sheets per side. Round up to a whole sheet, then double for both sides of the gable.
| Step | Calculation | Result |
|---|---|---|
| Sheet length | 5.0 m slope + 0.075 m overhang | 5.075 m, order 5.1 m |
| Sheets per side | 12.0 m / 0.762 m cover | 16 sheets |
| Both sides | 16 x 2 | 32 sheets |
| With 10 percent waste | 32 x 1.10 | 36 sheets |
Worked example: 12 m long gable, 5 m slope, Trimdek (762 mm cover)
Tip
For hip roofs, valleys and complex shapes, add more waste, around 15 percent, because angled cuts produce more offcut. When in doubt, send your roof plan to the CSA trade desk and we will do the takeoff for you for free.
3. Do not forget the accessories
The sheets are only part of the order. The items most often forgotten are the ones that hold up an install when they are missing. Build your accessory list at the same time as your sheet takeoff.
- Roofing screws: count the fasteners per sheet from the fixing pattern, plus 10 percent. Use the correct length and coating for your substrate and coastal zone.
- Ridge capping: measure the ridge length, order in standard lengths with overlaps.
- Barge and hip flashings: measure each edge.
- Valley gutter: measure each valley length.
- Foam closures and sealant for ridge and apron details.
- Gutter, downpipe, brackets and stop ends for the rainwater system.
- Sarking or insulation if required for NCC compliance.
4. Cut-to-length versus standard lengths
Stock sheets come in standard lengths, typically 1.8 m up to 9.0 m in 0.3 m steps. If your slope length matches a standard length closely, ordering stock is fastest and cheapest. If your slope falls awkwardly between standard lengths, or you want to avoid end laps on a long run, order cut-to-length so each sheet is made to your exact dimension. CSA cuts to plus or minus 5 mm on orders of 10 sheets or more.
Note
Avoiding end laps matters most on low-pitch roofs, where lap joints are the most common leak point. On a long, low-pitch run, single cut-to-length sheets with no end lap are worth the small premium.
5. Place the order
Once you have your sheet count, lengths, fasteners and flashings, you can buy stock items directly or request a quote for custom-cut and large orders. Trade account holders get volume pricing and priority dispatch. If anything in your takeoff is uncertain, the CSA trade desk will check it before the order goes to production so you are not short on the day.