Roofing calculator
Membrane roll quantities with explicit side and end laps, layers, upstand area and cutting allowance.
By Feroz Sheikh · Formula GCC-MEMBRANE-001 v1.0.0 · Tested formula
GCC-MEMBRANE-001v1.0.0Enter your measurements. Switching units converts the same project, including coverage and unit rates. Package yields keep the unit printed beside each field.
Calculated result
Membrane rolls to order
GCC-MEMBRANE-001rolls = ceil((roof area + detail area) × layers × (1 + waste/100) / ((roll width − side lap) × (roll length − end lap)))
Measured surface and details
Effective coverage per roll
Area including layers and cuts
Planning estimate, not engineering advice. Confirm site measurements and product specifications. Calculation limits.
Use the selected roll dimensions and specified laps to estimate a conservative effective coverage. Add measured upstand/detail area and cutting waste before rounding up to whole rolls.
Enter supplier prices and any labour, equipment or delivery costs. Pick a currency — badges, inputs, and totals follow.
Costs use the square, bundle or panel rate you type. Construclytic does not fetch shingle or metal prices. Tear-off, dumpsters, starter and flashing stay separate estimate lines. For GCC projects, select QAR, AED, SAR, KWD, OMR or BHD and enter local supplier rates.
How this calculator works
Feroz SheikhWritten by Feroz Sheikh · founder
Use the selected roll dimensions and specified laps to estimate a conservative effective coverage. Add measured upstand/detail area and cutting waste before rounding up to whole rolls.
GCC-MEMBRANE-001 explicitly removes side and end laps from effective roll coverage. It then shows detail area, layer count and cutting allowance separately so a nominal ten-square-metre roll is never assumed to cover ten finished square metres.
This separate example uses the calculator's starting values in imperial units. It stays unchanged when you edit the tool above. Example rates, yields and dimensions are assumptions, not recommendations for your project.
| Input | Example value |
|---|---|
| Roof length | 32.808399 ft |
| Roof width | 32.808399 ft |
| Additional detail area | 0 m² |
| Roll width | 1 m |
| Roll length | 10 m |
| Side overlap | 100 mm |
| End overlap | 150 mm |
| Membrane layers | 1 count |
| Cutting allowance | 10 % |
Example result: Membrane rolls to order — 13 rolls.
rolls = ceil((roof area + detail area) × layers × (1 + waste/100) / ((roll width − side lap) × (roll length − end lap)))
Use the labelled units above when reproducing this example. To work in metric, switch the calculator to Metric; applicable measurements are converted, while product-specific units remain labelled.
Need the broader workflow? Read the roofing planning guide.
Questions
Overlapping strips consume material. The calculation deducts one side lap and one end lap per roll, a conservative repeating-roll estimate that does not recover exposed boundary edges.
No. They are examples for a cited product. Replace them with the overlaps required by the actual system and substrate details.
This waterproofing membrane calculator publishes formula GCC-MEMBRANE-001, version 1.0.0. The ID stays on the result and on the estimate line.