Solar panels on flat roof vs pitched roof: which is better?

Roof type drives racking, angle, rain/snow shedding, and ultimately ROI. Here's when each wins.

Pitched roof (the default)

About 80% of US single-family homes have pitched roofs. Panels mount on flashed lag bolts into the rafters. Pros: cheap racking ($45-90/panel), built-in tilt, perfect water shedding.

• Racking cost per panel: $45-90
• Tilt: roof slope (typically 18-30°)
• Azimuth: locked to roof face (can be limiting)
• Install time: 1 day for 5-8 kW

Flat roof (flexible)

Flat roofs let you pick tilt and orientation. Trade-off: pricier racking and ballast or anchored mounts for wind.

• Racking per panel: $80-150 (triangular + ballast)
• Free tilt: 10-15° (looks + wind) or 30° (yield)
• Free azimuth: huge advantage
• Risk: membrane puncture if anchors are sloppy

East-west on flat roof

Very popular technique: two rows at 10° facing east and west. More panels per square foot (+40% density), flatter production curve, great aesthetics. Loss vs south optimum: 8-12%, easily recovered by fitting more panels.

Which to pick

Pitched roof facing south or southeast: pitched wins on cost. Pitched facing north: flat (with racking above ridge) wins. Big flat roof + daytime consumption: east-west at 10°, no doubt.

Before deciding, see optimal orientation and tilt and remember maintenance (flat panels accumulate more grime).