SettingsSettings for this calculationUS
The total roof area to be covered with base sheet.
Measure the full roof deck area receiving the built-up roofing base ply.
The usable coverage area per roll after the manufacturer's standard side and end laps.
This is the net area each roll actually covers once its built-in overlap allowance is accounted for, as specified by the manufacturer.
Extra material to allow for additional side/end laps and trim waste.
Accounts for lap requirements beyond the sheet's net coverage rating, plus cutting waste at edges, penetrations, and hips or valleys.
Base sheets needed
12 sheets
They open the calculator with your figures already in it
Built-Up Roofing (BUR) Base Sheet Calculator: 12 sheets — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Sheet count = ceil((roof area × (1 + overlap allowance)) ÷ sheet coverage area), accounting for the mandatory side and end laps between adjacent base sheet plies in a built-up roofing system
Inputs used
- Roof Area
- 1080 sq ft
- Sheet Coverage Area (Net of Standard Overlap)
- 100 sq ft
- Additional Overlap/Lap Allowance (%)
- 10
What this calculation does not cover
- Felt is the cheaper half of a built-up roof. The plies are bonded with hot asphalt or a cold adhesive at a rate the specification sets for each ply, and that bitumen is usually the larger part of both the weight going up the hoist and the invoice — a sheet count with no mopping quantity behind it leaves the kettle idle and the crew waiting.
- Fastener quantity is not one number across the roof. Where the base sheet is mechanically attached, the uplift design tightens the pattern along the perimeter and tightens it again in the corners, so a field spacing applied to the whole area under-counts fasteners in precisely the two zones where a roof starts to peel.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Part of bigger jobs
This trade is one line of several job takeoffs. Run the whole job and every other trade comes back with it, off the same measurements.
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Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.1.1
Regulatory standards & verification citations1
- Sheet count = ceil((roof area × (1 + overlap allowance)) ÷ sheet coverage area), accounting for the mandatory side and end laps between adjacent base sheet plies in a built-up roofing system
Cite this page
Your workspace
Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.
Tools and safety for this job
To lay a hot-applied bitumen membrane. Generic types, no brands, no prices.
Protection this work requires
- Torch work ignites dust and joists hours later: use a heat mat, keep an extinguisher to hand, and re-check the area an hour after the last flame.
- Most fatal falls on small jobs are from under three metres: use a tower or a ladder tied at the top, and never work off the top two rungs.
Lay a hot-applied bitumen membrane: This site does not publish a tool list for torch-applied roofing. A gas torch on a roof is hot work that starts fires in timber decks, insulation and eaves hours after the crew has gone; it is done by roofers trained for it, under the hot-work controls the insurer and the site set, with a fire watch after the torch goes out. Cold-applied and self-adhesive membranes remove the flame altogether.