Roofing & Solar
The top of your house does two jobs: it keeps the weather out, and it can quietly power the home under it. Start with how much usable roof you have.
Calculators for This Category
Practical Guides
Field guides for roofing & solar are being written. In the meantime, the solar sizing calculator carries its own worked example, assumptions table and FAQ on the tool page — the same standard we apply everywhere.
Solar planning and roofing are the same measurement problem: how much usable, structurally sound roof area do you have? Panels live on the roof, so start with the roof. Our calculator handles tilt, shading and efficiency losses once you know your area.
Roof Pitch Multiplication Factors
Roof area is bigger than its footprint. Measure the building footprint (length × width), then multiply by the factor for your pitch. These multipliers are the standard published values used across the roofing industry.
| Roof pitch | Angle | Multiplier |
|---|---|---|
| 4 / 12 | 18.4° | 1.054 |
| 6 / 12 | 26.6° | 1.118 |
| 8 / 12 | 33.7° | 1.202 |
| 10 / 12 | 39.8° | 1.307 |
| 12 / 12 | 45.0° | 1.414 |
Typical residential guidance only — a roof replacement, structural load check or grid connection should always be confirmed with a qualified roofer or engineer.