The short answer: yes, provided the roof and its covering are sound enough to carry the system for its whole life. So the roof is checked before any panel goes on, and a covering close to wearing out is refurbished or renewed first, with every detail made good, because lifting an array off later is a job of its own.
Why does the roof come before the panels?
Because the panels are likely to outstay a tired covering, and once they are fixed down the roof beneath them is hard to reach. Taking an array down so the roof can be re-covered, then putting it back up, spends money on something you already had.
So the sensible order is roof first. Before anything is fixed down, someone works out how much life the covering has left. A roof with plenty to spare may only need a few details put right; one near the end is dealt with while it is still open to the sky. On a block the same logic runs across a larger roof and every flat beneath it. The options for refurbishing a flat roof explain how that decision is reached.
What does the inspection look at?
All of it, not just the area the panels will cover, because water travels and every part of the covering ends up under the array or beside it. In practice the inspection checks:
- The covering: its condition, and whether it is still bonded down or has started to lift, blister or split.
- The insulation: any that is wet or has failed, which tends to show as soft or spongy patches underfoot.
- Falls and ponding: whether rain runs off, and where it stands instead.
- Outlets: whether each one drains freely.
- Upstands and edges: where the covering rises up a wall, and the trims around the perimeter.
- The deck: the boarding under the covering, and whether it is sound.
A building manager who needs those findings on paper can have the same checks written up in a condition survey.
What happens to the details before installation?
They are finished before the installer arrives, since a detail behind a frame is one nobody will look at for years. Outlets, parapets and upstands, chimneys and other penetrations, and movement joints are all made sound, and reinforced wherever the waterproofing system calls for it.
Ballast or brackets: how are the panels held down?
In one of two ways, and each asks something different of the roof. Ballasted frames are held in place by weight, so they need not pass through the waterproofing at all; the price of that is load. Fixed brackets are anchored through the covering into the structure, so every fixing becomes a penetration that has to be detailed on its own.
Whether the roof can carry ballast is a question for a structural engineer, never for a roofer. That check takes in the panels, the frames, any ballast and snow, together.
Where brackets and cables do pass through, cold-applied liquid waterproofing earns its place. It is worked around each fixing as a liquid and cures into a single joint-free piece, with no open flame near details that may be combustible.
How does the roof stay maintainable under an array?
By planning for it in the layout. Frames and ballast stand on a protection layer so they cannot wear into the covering, and walkways keep a clear route to every outlet.
Drainage needs the same thought. Frames, ballast and cable runs laid across the falls can hold water back from the outlets and leave it ponding, so the rows should leave open paths for rain to reach them.
Why put the roof right before rather than after?
Because afterwards much of it is out of sight. Under an array, a split or a lifting seam goes unnoticed until it shows as a stain indoors, by which time the water has had a long run.
Keep a dated photographic record of the roof's condition before installation. It helps the owner plan, and it settles any later disagreement about what was already there and what arrived with the panels. For a building manager, it belongs in the building file beside the installer's paperwork.
What changes about maintenance once the panels are on?
Inspections have to look under the array as well as around it. In the shade of the panels the covering dries slowly and gets little air, so dirt, moss and other growth gather there, and outlets need keeping clear.
Where there is room between the rows, a fault in a liquid-applied membrane can often be repaired locally without disturbing the panels. That depends on access, which is one more reason to leave some.
Who does what on a solar project?
We inspect the roof, put right or renew the covering, and waterproof the details around supports and cables. We do not design, supply or install solar panels, and we do no electrical work; structural checks belong to a structural engineer. Planning, building regulations and fire safety are dealt with by the installer and the relevant approvals.