The commercial solar site survey — what happens, and what can derail your quote

Every commercial solar quote before a site survey is an estimate. The survey is where someone climbs onto your roof, opens your electrical cupboard, and finds out whether the project the salesperson described is actually buildable at the price quoted. Knowing what they check — and what tends to go wrong — lets you spot a thorough survey from a superficial one, and avoid nasty "extras" appearing after you've signed.

What the surveyor actually checks

A proper commercial survey covers five areas:

1. The roof — type, age, condition, and structure. What's it made of, how old is it, and how much life is left? Critically, can it bear the load of panels plus mounting plus ballast plus wind and snow forces? On older or lightweight roofs this is the make-or-break question, and it may need a structural engineer's sign-off, not just a visual check.

2. Orientation, pitch, and shading. Which way does the roof face, at what angle, and what shades it — parapets, plant, flues, neighbouring buildings, trees? Shading doesn't just cut output from the shaded panels; depending on wiring it can drag down whole strings. The surveyor should note shading through the day, not just at the moment they're standing there.

3. The electrical setup. Where's the incoming supply, and does your switchgear and distribution board have the spare capacity to take the solar connection? If your board is full or your supply is constrained, you may need an upgrade — a real cost that should surface now. They'll also note your meter type and MPAN.

4. Grid connection (DNO). For commercial-scale systems, connecting and exporting needs Distribution Network Operator approval (the G99 process). The surveyor should flag whether your local network can accept the export or whether reinforcement might be needed — often the longest lead-time item in the whole project. (More in planning permission for commercial solar.)

5. Access and routes. How will they get panels onto the roof, where does the scaffolding or access equipment go, and how will cables run from roof to switchgear? Awkward access drives cost.

The thing that catches older buildings: asbestos

If your building dates from before 2000, the roof may contain asbestos. That doesn't necessarily stop the project, but it changes how the work is done (and priced), and it must be identified before anyone drills into the roof. A survey that ignores this on an older building isn't a thorough one.

What to have ready

You'll get a faster, more accurate survey — and quote — if you have these to hand:

• Recent electricity bills, and ideally half-hourly consumption data from your supplier. This is gold: it lets the installer size the system and model self-consumption properly (see south-facing vs east-west).
• Roof plans or drawings, and the roof's age and any recent works.
• Any structural information you have about the building.
• Your MPAN (the supply number on your bill) for the DNO side.
• Knowledge of any planned roof works or building changes — if you're re-roofing in three years, say so now.

The findings that change everything

Five survey outcomes commonly move the price or the decision:

1. The roof needs replacing soon. Panels last 25+ years; removing and refitting them to re-roof is expensive. If the roof has under ~10 years left, do the roof first.
2. Asbestos. Manageable, but it affects method and cost.
3. Insufficient structural capacity. May require strengthening, or a lighter system, or ground-mount instead.
4. Electrical capacity shortfall. A switchgear or board upgrade can add thousands.
5. DNO constraint. If the grid needs reinforcement, that's cost and delay — better known now than after you've committed.

After the survey: the quote should firm up

The whole point of the survey is to convert an estimate into a fixed, all-in price. After it, the proposal should account for scaffolding, any electrical upgrade, any structural work, and the DNO position — with no "we'll see after install" caveats left hanging. If extras can still appear later, that's a flag. Use our reading a commercial solar quote guide to pressure-test the post-survey numbers.

Sanity-check questions for your surveyor

1. Have you confirmed the roof can take the load — visually, or does it need a structural engineer?
2. Is there asbestos, and how does that affect the work? (Older buildings.)
3. Does my switchgear have capacity, or is an upgrade needed?
4. What's the DNO position and likely connection timeline?
5. Is this quote now fixed and all-in, or could there be extras after install?

The bottom line

A good site survey protects you: it surfaces the roof, structural, electrical, asbestos, and grid issues before you commit, and turns a salesperson's estimate into a price you can rely on. Have your bills and roof information ready, ask the five questions above, and treat any survey that skips the structure or the grid connection as incomplete.

To get an indicative figure before the surveyor visits, run the calculator. For the financial reliefs that apply once you proceed, see grants and funding, and subscribe to the Brief for ongoing guidance.

General information, not structural or electrical advice. Rely on your installer's qualified survey and any specialist reports.