Project Inputs
Typical: 1000 mm (39.37 in).
Typical: 10 m (32.81 ft) per roll.
Common side lap 75–100 mm.
Common end lap 100–150 mm.
Average number of end laps each roll experiences.
Set 1, 2, or 3 layers as required.
Covers offcuts, detailing, and site losses.
Add contingency rolls on top of calculation.
Roof Areas
| Label | Length (m) | Width (m) | Qty | Area (m²) | Action |
|---|---|---|---|---|---|
| Total area | 0.00 m² | ||||
Results
Effective roll width
— m
Effective roll length
— m
Coverage per roll
— m²
Total design area
— m²
Required rolls (including layers and waste)
—
Includes spare rolls if specified.
| Metric | Value | Units |
|---|
Example Data
These example roof segments can be loaded into the calculator.
| Label | Length (m) | Width (m) | Qty | Area (m²) |
|---|---|---|---|---|
| Main Roof | 18 | 9 | 1 | 162 |
| Terrace | 8 | 3 | 1 | 24 |
| Lift Machine Room | 4 | 3 | 1 | 12 |
| Parapet Caps | 30 | 0.4 | 1 | 12 |
| Total | 210 | |||
Formulae Used
- Effective width = RollWidth − SideLap
- Effective length = RollLength − (EndLap × EndLapsPerRoll)
- Coverage per roll = EffectiveWidth × EffectiveLength
- Design area = Σ(AreaSegments) × Layers × (1 + Waste%)
- Required rolls = CEILING( (DesignArea ÷ CoveragePerRoll) ) + SpareRolls
Notes: All lap dimensions are treated as overlaps that reduce net coverage. Waste covers offcuts, detailing, penetrations, and site losses.
How to Use
- Select units. Enter roll dimensions and required overlaps.
- Enter layers, waste, and any spare rolls for contingency.
- Add roof areas using Length, Width, and Quantity for each segment.
- Click Calculate to see coverage and roll counts.
- Export results as CSV or save a PDF via Save as PDF.
- Adjust inputs to test scenarios, such as different lap allowances.
FAQs
Yes. Add as many segments as required. Each row supports length, width, and quantity. The total area is then used in the design area calculation.
Overlaps reduce net coverage by narrowing effective strip width and shortening effective strip length. The calculator deducts laps before computing coverage per roll.
It is the expected count of end overlaps encountered per roll when laying strips. One is common, but longer runs or many splices can increase this number.
Waste covers offcuts, detailing around penetrations, perimeter flashing allowances, and general handling losses. Increase this for complex detailing, windy roofs, or challenging access.
Yes. Toggle the units switch to enter inches and feet. The calculator converts values internally and shows areas in square meters for consistency.
Set the layer count to match your system. For example, two layers for base and cap. The required rolls reflect total layers across the whole area.