Roofing
Flat Roof Cost Calculator
Price a low-slope roof from membrane type, insulation, attachment method and the drainage detail.
Result
A planning estimate, not a quote. Access, the age of the equipment, what is found once it is opened up and local labour rates all move the real figure, sometimes a long way.
Get a Free Business AuditWhat moves the number
- Membrane system, since each has different material and installation cost.
- Insulation thickness and taper, which on a flat roof can exceed the membrane cost.
- Attachment: mechanically fastened, fully adhered or ballasted.
Where this one goes wrong
Pricing the membrane and treating drainage as a detail. A low-slope roof that ponds will fail early regardless of the membrane, and correcting the falls with tapered insulation is a significant cost that has to be in the quote.
Before you quote
- Whether existing falls actually drain, or whether the roof ponds.
- Drain and scupper condition and capacity.
- Whether the existing build-up has to come off or can be recovered over.
Questions
About this calculator
Why does ponding matter so much?
Because standing water accelerates membrane degradation, adds load and finds every weakness in a seam. A membrane installed over inadequate falls will not reach its expected life.
What drives flat roof cost most?
Frequently the insulation rather than the membrane, particularly where tapered insulation is needed to create falls. It is easy to underestimate because it is invisible in the finished roof.
Can a flat roof be recovered rather than stripped?
Sometimes, subject to code limits on layers and the condition of what is underneath. Recovering hides the existing condition, so it needs a survey rather than an assumption.
The formula
total = hours x people x rate + parts + call-out, then sales tax
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How to use this calculator
- Hours on site (h). Enter your own figure; the page starts at 26 h.
- People needed. Enter your own figure; the page starts at 1.
- Labour rate charged ($). Enter your own figure; the page starts at $95.
- Parts and materials ($). Enter your own figure; the page starts at $3,900.
- Call-out or diagnostic fee ($). Enter your own figure; the page starts at $95.
- Sales tax (%). Leave at zero if you are quoting before tax.
The result updates as you type, so you can try a figure, see what it does to estimated total, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Hours on site | 26 h |
| People needed | 1 |
| Labour rate charged | $95 |
| Parts and materials | $3,900 |
| Call-out or diagnostic fee | $95 |
| Sales tax | 0% |
What comes out
| Result | Value |
|---|---|
| Estimated total main result | $6,465 |
| Labour | $2,470 |
| Before tax | $6,465 |
| Sales tax | $0 |
About $6,465: $2,470 of labour, $3,900 of parts and a $95 call-out.
How sensitive the answer is
Holding everything else steady and changing only labour rate charged, this is what happens to estimated total. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Labour rate charged ($) | Estimated total |
|---|---|
| $48 | $5,243 |
| $71 | $5,841 |
| $95 example above | $6,465 |
| $143 | $7,713 |
| $190 | $8,935 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Hours on site (h)
- Measured in h, between 0 and 400, starting at 26 h.
- People needed
- A number, between 0 and 40, starting at 1.
- Labour rate charged ($)
- A money amount, starting at $95.
- Parts and materials ($)
- A money amount, starting at $3,900.
- Call-out or diagnostic fee ($)
- A money amount, starting at $95.
- Sales tax (%)
- Leave at zero if you are quoting before tax.
What the results tell you
| Result | What it is |
|---|---|
| Estimated total | The headline result. A money figure. |
| Labour | A money figure. |
| Before tax | A money figure. |
| Sales tax | A money figure. |
What this cannot see
Material quantities assume a clean rectangular plane and the waste factor you enter. Valleys, hips, dormers, penetrations and a steep pitch all raise real waste, and a tear-off frequently uncovers decking that was not in the quote.
Estimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.