What happens during a solar survey

A solar survey is a technical inspection, not a sales visit. Over an hour or two a surveyor measures the roof properly, checks the structure from inside the loft, assesses the covering, models shading across the year, inspects the consumer unit and earthing, works out where cables and equipment will go, and reviews how your household actually uses electricity. The output is a design and a firm quotation for your property. A price given without any of that is a guess, and the gap between the guess and reality tends to appear as variations once the scaffolding is up.

Outside: the roof

The surveyor measures the roof rather than estimating it from a footprint. That means slope dimensions, pitch, orientation and the position of everything that interrupts the surface — ridges, hips, valleys, verges, chimneys, dormers, rooflights, vent tiles, soil pipes, aerials and dishes.

The covering matters as much as the dimensions. Concrete interlocking tiles, plain clay tiles, natural slate and profiled metal all need different fixings and different levels of care. Condition matters too: a covering with widespread cracked or delaminating units needs attention before an array goes on top of it, because taking an array off to repair a roof later is expensive.

Height and the surrounding ground are recorded for access planning.

Inside: the loft

This is the part that gets skipped by the surveys that are not really surveys.

In the loft the surveyor checks rafter size, spacing and condition, because fixings go into rafters and the layout has to line up with them. Sagging, previous alterations, water staining and the state of the underfelt all show up here. So does the practical route for DC cable, and whether the loft is a sensible place for the inverter — ventilation, temperature and access all bear on that.

Where there is no loft access — a room in the roof, a sealed cassette — that changes the design and needs to be known early.

Shading

Obstruction positions and heights are recorded and modelled against the sun path across the whole year, not judged by what the roof looks like on the afternoon of the visit. A tree that clears the array in June can sit across it for most of a December day.

The output is a shading assessment that feeds into the layout, the stringing and whether module-level electronics are worth specifying.

The electrical side

The surveyor inspects the consumer unit: type, condition, available ways, protective devices, and whether it is serviceable, full, or due replacement anyway. Main earthing and bonding are checked, because inadequate earthing has to be corrected as part of the work.

The incoming supply is identified — single or three phase — along with the main fuse rating and the meter position. That, together with the proposed system size, establishes whether the installation falls under G98, where the DNO does not have to be contacted in advance and the installer submits an Installation Commissioning Confirmation within 28 days of commissioning, or whether a G99 application is needed, which must be approved before installation.

Cable routes from array to inverter and inverter to board are worked out at this point, along with where isolators will sit.

Access and scaffolding

Where can a scaffold stand? Is there a side gate wide enough to carry materials through, or does everything go over the roof of a garage? Are there conservatories, boundary walls, neighbours’ land, overhead cables, or a driveway that has to stay usable?

Access is often the single largest non-equipment cost on a domestic job, and it cannot be priced from a photograph.

Planning status

The surveyor establishes whether the property is listed, in a conservation area or subject to any local restriction. Roof solar on residential buildings may be permitted development subject to limits and conditions, but listed buildings, conservation areas and World Heritage Sites carry additional restrictions and may require consent — and where that applies it shapes the design rather than following from it.

Your electricity use

Finally, the conversation. Annual consumption in kWh, half-hourly data if you have it, your tariff, who is home during the day, whether there is an EV or one planned, whether a heat pump is under consideration, and what you actually want the system to do.

This is what turns a roof layout into a system design. It determines array size, whether storage makes sense, what capacity, and what inverter architecture suits.

What you get afterwards

A design showing the array layout on your roof, the equipment specification, a performance estimate produced by the standard method with its assumptions stated, the network route, and a fixed quotation that identifies anything excluded.

If we find something that means we would not recommend proceeding — a roof that needs re-covering first, shading that undermines the case — we will tell you at that point.