01
The mounting system is a structural decision
Mounting hardware is rarely the biggest line in a quotation, but it is where the risk sits. It transfers wind and snow loads into the building, it determines whether the roof stays watertight, and it decides how the array is accessed for the next twenty five years.
Every commercial installation should be backed by a structural assessment of the existing roof and its supporting frame, taking account of the added dead load and the wind uplift on the array.
If the roof cannot take it, the answers are a lighter system, a reduced array, strengthening, or a different location such as a car port or ground mount. All of them are better than proceeding on optimism.
02
Flat roofs and ballasted systems
On flat membrane roofs, ballasted frames hold the array in place with weight rather than fixings, avoiding penetrations. Row spacing is set to limit self shading, which is why flat roofs need more area per kilowatt than pitched ones.
East to west configurations lay panels in facing pairs at a shallow angle. They pack more capacity onto the same roof and produce a flatter generation curve across the day, which often suits a commercial load better than a south facing peak.
Ballast is dead load, so the structural calculation is central and the wind uplift assessment must reflect the building's height, exposure and parapets rather than a generic figure.
03
Pitched, metal and standing seam roofs
Profiled metal roofs are usually the simplest case. Non penetrative clamps grip the standing seam, keeping the roof sheet intact and the manufacturer's warranty in place, with loads spread along the seam.
Trapezoidal profiles take rail systems fixed through the crown with weatherproof seals. Detailing matters, since every fixing is a potential leak if it is done badly.
On slate, tile or older composite roofs the assessment covers both the covering and the structure beneath it. Fragile roofs are also a safety issue, and the access and fall protection strategy needs settling before anyone is programmed onto site.
04
Wind, snow and the standards that apply
Loading is calculated to the relevant Eurocodes and their UK national annexes, using the site's exposure, altitude, building height and terrain. A coastal warehouse and an inland unit with the same roof area do not get the same design.
Edge zones and corners see the highest uplift, which is why arrays are set back from perimeters and why ballast is often heavier at the edges. Setbacks also leave the access routes that maintenance and fire strategy require.
Ask for the loading calculations as part of the proposal. A design that cannot show them has not been done properly.
05
Access, maintenance and roof life
Design in the walkways. An array installed edge to edge with no access routes makes cleaning, inspection and repairs slow and expensive, and it can conflict with the roof's fall protection arrangements.
Match the system life to the roof life. Fitting a twenty five year array over a covering with under a decade left commits you to lifting and refitting it, which is why re roofing and installation are sometimes better done as one project.
Where the roof is under warranty, the installer should obtain the roofing manufacturer's written agreement to the mounting method before work begins.
Estimate it for your own building
Draw your roof in the free assessment below and we will show an indicative system size, generation, saving and payback before anyone visits site.
