Is Your Roof Ready for Solar? The Complete Roof Assessment Guide

Your roof is the foundation of your solar installation - and it needs to be in good shape. A qualified installer will assess your roof during the site survey, but understanding the key factors beforehand helps you make informed decisions and avoid surprises.

Roof Age and Condition

Solar panels last 25-40 years. If your roof needs replacement in less than 10 years, you should replace it before installing solar. Removing and reinstalling solar panels for a roof replacement costs $2,000-$5,000 and risks damaging the system. Asphalt shingles (most common): typical lifespan 20-30 years. If your shingles are 15+ years old, consider replacing before solar. Metal roofs: excellent for solar with 40-70 year lifespans. Solar mounting on metal is actually simpler than on shingles. Tile roofs: 50+ year lifespan. Solar can be installed on tile but requires specialized mounting hardware and experienced installers - tiles are fragile and can crack during installation. Flat roofs: Solar works well with tilted mounting systems that angle panels toward the sun. Ballasted systems (weighted down, not penetrating the roof) are common on flat roofs.

Roof Orientation

The direction your roof faces dramatically affects solar production. South-facing: 100% optimal production. The gold standard for solar in the northern hemisphere. Southwest or southeast-facing: 90-95% of optimal. Still excellent. West-facing: 80-85% of optimal. Good production, with a bonus: peak production shifts to afternoon, which aligns well with time-of-use peak rates. East-facing: 75-80% of optimal. Acceptable, with peak production in the morning. North-facing: 50-65% of optimal. Generally not recommended unless you have no other options and live in the southern U.S.

Most homes have multiple roof faces. A good installer designs a system that uses the best-oriented sections and avoids the worst. Split installations across multiple roof faces are common and work well.

Shading Analysis

Shading is the single biggest production killer. Even partial shading on a few panels can disproportionately affect the entire system (depending on inverter type). Tree shading: The most common issue. Evaluate trees to the south, southeast, and southwest of your home. Remember that trees grow - a tree that doesn't shade your roof today may shade it in 5-10 years. Trimming or removing shade trees can increase solar production by 10-30%. Building shading: Nearby buildings, chimneys, satellite dishes, and HVAC equipment on the roof can create shading. These are usually easier to work around in system design. Self-shading: On roofs with dormers, valleys, or complex geometry, one section of roof can shade another at certain sun angles. Good system design avoids placing panels in these zones.

Structural Considerations

Solar panels add 3-5 pounds per square foot to your roof load. Most roofs can handle this without modification, but some situations require structural reinforcement. Older homes with deteriorated rafters, roofs already carrying heavy loads (multiple shingle layers, heavy HVAC equipment), and flat roofs with long spans may need engineering review. Your installer should assess structural adequacy during the site survey. If there's any doubt, a structural engineer review costs $300-$500 and provides peace of mind.

Available Roof Space

Each solar panel is roughly 18 sq ft (3.5 x 5.5 feet). A typical 8 kW system using 20 panels needs about 360 sq ft of usable roof space. "Usable" means areas with good orientation, minimal shading, sufficient distance from roof edges (fire code setbacks), clear of vents, skylights, and other obstructions, and structurally sound. If your usable roof space is limited, higher-efficiency panels (SunPower at 22.8%) produce more power per square foot, allowing you to fit a larger system in a smaller area.