A useful roof assessment combines an energy estimate with a physical survey. A sunny map cannot tell you whether a roof is structurally suitable.
Start with what surrounds you
Note trees, nearby buildings, chimneys and roof features that cast shadows. Shading changes during the day and across seasons. Photograph the roof from safe ground-level positions; leave access and structural assessment to a competent professional.
Ask for roof-specific estimates
The European Commission’s PVGIS tool can help estimate solar production for a location and orientation. Use it as a starting point, not a substitute for an installation survey. Ask your installer to explain assumptions about shade, system losses and the area available for panels.
Coordinate with future work
A roof likely to need major repairs soon deserves attention before equipment is fitted. Ask whether access, scaffolding, waterproofing and future removal are covered. Also identify who will check any local permission requirements before a contract is finalised.
Compare useful roof areas separately
A roof may have several pitches with different orientations, slopes and obstacles. Ask for a layout and a production estimate for each usable area rather than a single panel count. A small, shaded extension should not be treated like an open main roof. Include access to chimneys, gutters and roof windows in the layout, along with any space the installer needs for mounting and maintenance.
Compare timing as well as annual output
Two layouts with similar yearly production can deliver electricity at different times. Ask to see monthly output and a representative daily profile for each option. Then place your household demand alongside it. This helps explain why the layout with the largest annual total may not deliver the largest reduction in purchased electricity. It also prevents a summer production graph being mistaken for an all-year pattern.
Turn the survey into a written scope
Separate the survey’s findings into work required before solar, work included in the solar contract and matters still to resolve. Possible items include roof repairs, scaffold access, cable routes and the inverter location. Ask who is responsible for checking the structure and weatherproofing. If an outbuilding is proposed, include the electrical route back to the home; a convenient roof can still involve substantial connection work.
Your planning checklist
- A panel layout for each roof face, showing obstructions.
- Monthly generation estimates with shading assumptions.
- A record of roof condition and any work needed first.
- Access, cable routing and survey responsibilities in the quote.
Common questions
Can a satellite image replace a roof survey?
It can help with an initial layout, but it cannot establish hidden roof condition, mounting details or structural capacity. Use the desktop estimate to prepare questions for the site assessment.
Should I repair an ageing roof first?
Compare the expected repair timetable with the cost of removing and refitting panels later. Ask the roofer and solar installer to agree the sequence and warranty responsibilities before either job is booked.