How much roof space do I need for solar panels?

Each modern 400W panel occupies approximately 1.75m². A typical 4 kWp system (10 panels) needs about 17.5m² of usable roof space. A 6 kWp system needs about 26m². You need to deduct setbacks from edges (300mm+) and area around obstructions.

How do I measure my roof for solar panels?

Measure the south-facing roof plane width and rafter depth. For a pitched roof, the slope area = depth ÷ cos(pitch angle). Deduct setbacks (typically 300mm from all edges), obstructions (chimneys, vents, dormers) and any areas that are heavily shaded.

Can I put solar panels on a hip roof?

Yes, but hip roofs have less usable area than gable roofs because the triangular sections at each end are mostly unusable. A hip roof typically has about 75% of the usable area of an equivalent gable roof. The central rectangular section provides the most usable space.

What setback is needed from the roof edge?

MCS guidelines recommend a minimum 300mm setback from all roof edges for safety and wind loading. Some installers use 500mm, especially on exposed sites. Building regulations may require greater setbacks near boundaries. Check with your installer for site-specific requirements.

Can solar panels go on a flat roof?

Yes, panels are mounted on angled frames (typically 10-15°) on flat roofs. Flat roofs allow flexible orientation but require row spacing to avoid inter-row shading (typically 1.5-2x panel height). This means fewer panels per m² than pitched roofs, but you can choose optimal orientation.

TradeCalculator

Solar Roof Area Calculator

Calculate available roof area for solar panels accounting for roof type, pitch, obstructions and setbacks. Determine maximum panel count and system size.

Roof Type

Gable gives most usable area

Roof Width

Width of south-facing plane

Roof Depth (horizontal)

Horizontal depth (eave to ridge)

Roof Pitch

0 for flat roof

Obstructions

Chimneys, vents, dormers

Price per Panel

How We Calculate This

This calculator determines the maximum solar panel count based on available roof area.

The formula

Usable area = (Gross area × Roof factor) - Setbacks - Obstructions

Slope area = depth ÷ cos(pitch)
Hip roof factor: 0.75
Setback: 300mm from all edges
Panels: usable area ÷ 1.75m² per panel

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.