Solar Panels on Metal and Profile Roofs

What we mean by a profile roof

Sheet metal roofing covers a wide range of buildings: agricultural barns and converted ones, workshops, garages, light industrial units, and an increasing number of contemporary houses. The common feature is a thin metal covering spanning between purlins rather than a covering laid over a deck.

The mounting question splits cleanly by profile. Standing seam is clamped. Trapezoidal and corrugated sheet is through-fixed. Which one you have determines the method, the cost and the risk.

Standing seam and non-penetrating clamps

A standing seam roof has raised, folded upstands running up the slope, with the sheet itself held down by concealed clips rather than exposed fasteners. Purpose-made clamps grip that seam, tightened against the upstand, and carry the mounting rail above.

Nothing penetrates the sheet. That is the significant advantage: the weathering layer is not breached at any point, so the leak risk associated with roof mounting largely disappears.

Two conditions attach. The clamp has to match the seam profile — seam systems vary and a generic clamp is not acceptable. And the sheet’s own clips have to carry the array uplift, because the load path now runs seam to clip to purlin. On a lightly fixed roof that needs checking rather than assuming.

Trapezoidal and corrugated sheet

Here the fixing goes through the sheet. A bracket or short rail sits on the crown of the profile, fastened with a self-drilling screw carrying a bonded EPDM sealing washer, compressed correctly — under-tightened leaks, over-tightened deforms the washer and leaks later.

Where the sheet gauge is light or the uplift high, the fixing should continue into the purlin beneath rather than relying on the sheet. Purlin positions therefore constrain the array layout in the same way rafter centres do on a tiled roof, and locating them accurately is part of the survey.

Insulated composite panels are a further case: the fixing passes through an outer skin, an insulating core and sometimes an inner liner, and the fastener has to be specified for that build-up.

Thermal movement

Metal sheet expands and contracts with temperature far more than tile or slate, and the movement over a long slope is measurable. A mounting system rigidly clamped at both ends of a long rail restrains that movement, and something eventually gives — usually the sheet at a fixing, or the coating around it.

Rails are therefore run in lengths that accommodate movement, with expansion joints where required by the mounting manufacturer. On standing seam this matters especially, because the roof system itself is designed to move over its clips.

Corrosion and material compatibility

Coated steel and aluminium sheet corrode quickly in contact with an incompatible metal in a damp environment. Copper is the obvious offender; unprotected mild steel is another. Aluminium rail with stainless fasteners and isolating components is the standard approach, and it matters more here than on any other covering because the roof itself is the metal at risk.

Cut edges, existing fixings and lap details are the points to inspect. Weeping fixings and perished washers tell you the coating is at the end of its useful life.

Design, access and limitations

Profile roofs are frequently large and unbroken, allowing simple rectangular layouts across multiple strings and MPPT inputs. Pitches are often shallow, so self-cleaning is reduced and cleaning access is worth planning.

Access is usually good at ground level, but sheet roofs are fragile to walk on and rooflights are a serious hazard, requiring covers, staging or a fall arrest system.

Honest limitations: some seam profiles have no matching clamp, some sheets are too thin to fix to without purlin access, and cement sheet is a different matter entirely and not something to drill into. Where the covering is near the end of its life, replacing it first is the cheaper sequence.