Check the roof covering before the panels

Flat roofs

• Felt and asphalt. Look for blistering, cracking, splits at the edges and around outlets, and areas that hold water after rain.
• Single-ply membranes. Check the seams and the edges, and ask what the manufacturer allows to sit on or be fixed through the membrane.
• The deck. Soft spots underfoot (seen by a roofer, not by you walking on it) mean rot in the boards beneath.
• Drainage. Frames and ballast must not dam water against upstands or block outlets.

Pitched roofs

• Concrete tiles. Common on later twentieth-century houses; check for slipped or cracked tiles and the state of the ridge and verge.
• Slates. Older houses may have slate; slipped slates in rows suggest failing nails.
• Underlay and battens. Old felt can be brittle; the installer will see it when lifting tiles for brackets.

Signs from the ground that a roof needs work first

• A sagging ridge or a dip in the slope.
• Slipped, cracked or missing tiles or slates, especially in lines.
• Daylight or damp patches visible from the loft.
• On a flat roof: standing water a day after rain, splits along the edges, or a covering that has been patched many times.

Any of these is worth showing to a roofer before an installer prices the job.

Questions for the roofer

• How many years does the covering have left, and would you renew it before panels go on?
• Can the deck and joists take ballasted frames, or should the frames be fixed through the covering?
• What protection should sit between the frames and the membrane or felt?
• Will your guarantee on the covering still stand once someone else has put frames on it?

Pitched roofs: what fitting involves

On a tiled or slated roof the installer lifts tiles, fixes brackets to the rafters beneath, and relays the tiles around them, often trimming or replacing a few. Ask how the brackets will be weathered where they pass between the tiles, whether broken tiles will be replaced with matching ones, and whether a few spares can be left with you. On interlocking concrete tiles this is routine; on old slate it needs more care, because slates crack easily and nails may already be failing.

Who answers for a leak

Once a roofer and an installer have both worked on a roof, a leak can become an argument about whose work caused it. Agree beforehand who is responsible for what: the roofer for the covering, the installer for anything fixed through or set down on it. Ask the installer for photographs of the covering before the frames go on, and keep both firms' warranties together.

Weight

Panels and rails on a pitched roof add a modest, spread load. Ballasted frames on a flat roof rely on weight to stay put in the wind, and that weight sits on the joists. The installer should say how much ballast is proposed and whether the structure has been checked.

Timing

Where both trades are needed, book the roof work first and the panels straight after, so the scaffolding or tower can serve both if the firms agree.

If the covering has only a few years left, renew it first. Re-roofing under an existing array means disconnecting it, moving it and refitting it, with access paid for twice. The Warm Homes Loan Scheme rules say it will not fund replacement roofing or structural work needed before solar.

Keep reading

• Flat-roof planner
• Measuring a flat roof
• Finding an installer
• Costs

Where the figures come from

1. DESNZ: Warm Homes Loan Scheme rules v3 (September 2026)
2. MCS: The Solar PV Standard (Installation), MIS 3002 v6.0
3. Legislation.gov.uk: GPDO 2015 Schedule 2 Part 14 (solar on homes)