A published “$650 a square” special prices the plan. A TPO or EPDM roof is not that number. It is a membrane mil that does not scale with squares, a recover or a tear-off, dry insulation or wet, and lineal feet of parapet the coupon never counted. Matching the coupon on an 80-mil TPO tear-off is how a sold job becomes unpaid welding time after the first parapet.
Open the free bid calculatorTake a 40×30 garage, TPO 45-mil, recover, two drains, no parapet. That is 1,200 plan square feet and 12 squares — 12.96 membrane squares after 8% waste. The coupon says about $7,800. Raise the same shop to an 80×50 two-story commercial deck at 1/2" per foot. The plan is 4,000 square feet, so the coupon says about $26,026 on 40.04 squares. The job did not scale that way: 80-mil membrane, a welder, a wet-insulation tear-off, two polyiso layers, 80 lineal feet of parapet, six drains, and four HVAC curbs the garage never had.
Put EPDM on that garage. Sheets now cost more per square the TPO-45 recover never priced. Two stories are not “the same squares plus a ladder.” A parapet is not in the square number at all.
The flat roof bid calculator does that arithmetic in the browser from your own hours and invoices. Starting waste, hours, and material rates are ballpark figures to replace, not a catalog or a code table.
This is not a building-code opinion, a permit, a construction specification, a wind-uplift rating, or an engineering stamp. Confirm the jurisdiction and a qualified professional before sending a price. The output is arithmetic on the numbers you typed.
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Start from the building plan, apply the low-slope factor to get roof squares, then count membrane squares after waste, tear-off, insulation layers, parapet flashing, drains, and the permit. A published $650 per square special only sees plan squares.
A 40-by-30 garage is 12 squares of TPO-45 recover. An 80-by-50 two-story commercial deck is 40.04 squares of 80-mil TPO, a wet-insulation tear-off, two polyiso layers, 80 lineal feet of parapet, and six drains. Matching the garage coupon is how the commercial job loses money.
No. Membrane rates, waste, and insulation figures here are common starting points on residential and light-commercial bids. They are not a building-code opinion, a permit, a wind-uplift rating, or an engineering stamp.