Practical tools for measured work
Single-slope roof layout and materials
Calculate single-slope roof area, entered-spacing rafter centres and effective-covering piece quantities.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
Rafter centre positions along bearing line
| Rafter | Position (mm) |
|---|---|
| 1 | 0 |
| 2 | 600 |
| 3 | 1200 |
| 4 | 1800 |
| 5 | 2400 |
| 6 | 3000 |
| 7 | 3600 |
| 8 | 4200 |
| 9 | 4800 |
| 10 | 5400 |
| 11 | 6000 |
How it works
This is one rectangular, single-slope roof plane. Rise and run are measured between bearing lines. Horizontal overhangs extend that slope; roof area uses the resulting slope length and the overall roof width. The plan diagram shows rafter centres along the bearing length.
Rafters are spaced equally with one at each end, never exceeding your entered spacing. This is a geometric count, not a code-derived spacing choice. The centreline slope length excludes seat cuts, ridge or ledger details, member thickness and cut allowances.
Enter the covering product’s effective installed coverage after laps, not its overall sheet size. Pieces are counted in a rectangular covering grid, with no assumed offcut reuse. The extra allowance rounds up to whole pieces. Confirm product slope limits, lap details and cutting layout with its manufacturer.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Horizontal run between bearing lines
- 3000 mm
- Rise between bearing lines
- 1000 mm
- Length along bearing lines
- 6000 mm
- Low-eave horizontal overhang
- 300 mm
- High-side horizontal overhang
- 0 mm
- Roof extension at each end
- 150 mm
- Entered maximum rafter spacing
- 600 mm
- Effective covering width per piece
- 1000 mm
- Effective covering length per piece
- 4000 mm
- Extra whole-piece allowance
- 10 %
Primary result: Roof slope length including overhangs: 3478.505 mm.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
No structural member, connection, flashing, drainage or waterproofing design is provided. End overhangs may require outriggers, doubled framing or other supports not counted here. Supports, species, grade, loads and local rules need a qualified design. Other roof shapes require separate planes and intersection details.
Frequently asked questions
What should I verify before using this result?
Recheck the physical measurements, confirm that every input uses the displayed unit, and compare the result with the applicable drawing, product specification, code requirement or test piece.
Why might the finished result differ?
Real work can include thickness, kerf, seams, tolerances, hardware allowances, installation clearances or site conditions that are outside the calculation. The limitations section identifies the main exclusions for this tool.
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