Skillion Roof Calculator
Calculate skillion (mono-pitch/shed) roof area, rafter length, and material quantities from span and pitch. Single-slope calculations with waste. Free, no signup.
Roof Area Calculator
Calculate actual roof surface area from plan dimensions and pitch
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Skillion roofs — did you know?
What is a skillion roof?
A skillion (mono-pitch or shed roof) has a single slope. It is the simplest roof form — one rafter length, one slope, no ridge. Common on extensions, modern homes, and agricultural buildings.
Skillion rafter calculation
Only one rafter length: rafter = span ÷ cos(pitch°). At 35° with 5m span: 5 ÷ cos(35) = 6.10m. Add overhang separately. No ridge, no hips, no valleys — simplest rafter calc in roofing.
Typical skillion pitches
Skillion roofs are often steeper than flat roofs but shallower than gable roofs: 10°-25° is common. Modern architecture favours low-pitch skillions (5°-15°) with metal roofing. Minimum pitch depends on material.
Drainage on skillion roofs
Water runs off one side only. Ensure the low side has adequate gutter capacity. At 15° pitch, a skillion sheds water almost as fast as a 15° gable — but ALL water goes to one side. Size gutters accordingly.
Formulas used
Roof area
area = span × length × (1 ÷ cos(pitch°))
Rafter length
rafter = span ÷ cos(pitch°)
Material quantity
qty = area × (1 + waste%) ÷ coverage
Water runoff (single side)
runoff = area × rainfall_intensity
Frequently asked questions
How do I calculate skillion roof area?
span × length × (1 ÷ cos(pitch°)). At 15°, 5m span, 10m length: 5 × 10 × 1.035 = 51.8 m².
What pitch for a skillion roof?
Typically 10°-25°. Modern homes: 5°-15° with metal roofing. Minimum depends on material — check manufacturer specs.
How is a skillion different from a gable?
Skillion = single slope (one rafter length, no ridge). Gable = two slopes meeting at ridge. Skillion is simpler but sheds all water to one side.
Best free skillion roof calculator?
One that handles single-slope area, rafter length, and materials. This tool does all, free.