Solar Panels on Metal Industrial Roofs: Trapezoidal, Standing Seam and Composite
Updated 23 October 2026 · SEO Dons Editorial
Which fixing suits which metal roof?
| Roof type | Usual PV fixing | Penetrates the sheet? | First check |
|---|---|---|---|
| Trapezoidal sheet | Short or long rails screwed to the crowns, each hole sealed | Yes | Gauge, crest width and condition of existing fasteners |
| Standing seam | Clamps matched to the seam profile | No, the clamp grips the seam | Roof manufacturer's approval of the clamp, and the roof's own clips |
| Insulated composite panel | Fixings reaching the substructure, or a method the panel maker has approved | Yes | Panel maker's written approval and the panel's fire listing |
How is PV fixed to a trapezoidal sheet roof?
On trapezoidal sheet the rails or clips are screwed through the raised crowns, so every fixing is a penetration that has to be sealed. Two layouts are common.
- Short rails. A short length of rail sits at each fixing point and the module clamps onto it, so no continuous rail crosses the roof; S-5! lists a rail-less metal roof solar mount, its PVKIT. K2's MultiRail is a short rail fastened with self-tapping sheet screws for pitches of 5 to 75 degrees on trapezoidal or sandwiched trapezoidal sheet, and its MiniRail comes with thread-forming screws and a sealing washer.
- Long rails. Rails run across several crowns. K2's BasicRail inserts into clips screwed to the roofing.
Enstall's system also uses screws through the sheet: its profiles have pre-punched holes and pre-applied EPDM rubber seals, and go on trapezoidal, sandwich and corrugated steel roofs with self-tapping screws.
Manufacturers publish minimums that a survey has to check. For MultiRail and BasicRail, K2 states a sheet thickness of at least 0.4 mm for steel and 0.5 mm for aluminium and a crest width of at least 22 mm, and for BasicRail a flush area at least 20 mm across around the hole. Thin, corroded or damaged sheet can therefore rule out sheet-only fixings.
MCRMA publishes advice note AN 07 on proof testing metal roofing and cladding fasteners and guidance document GD24 on purlins and side rails. It also says wind loading must be calculated for every building and needs a qualified engineer or software used by an experienced person. An array adds loads the original design did not include, so that check covers purlins and sheet fixings, not only the rails.
How do clamps work on standing seam roofs?
Standing seam sheets join at raised, folded seams, and clamps grip the seam rather than drilling the sheet; S-5!, a clamp maker, describes its standing seam clamps as non-penetrating.
Clamps are profile-specific. K2 lists clamps for double standing seams in titanium zinc, aluminium, stainless or galvanised steel, two-jaw clamps for Klip-Lok 406 type profiles, clamps for round bulb seams such as Kalzip, Bemo, Aluform and RIB-ROOF Evolution, and clamps for angled and snap seams. Enstall describes three clamp types covering single and double folded, snap and rounded seams.
A clamp avoids a hole, not a load path. It passes wind uplift and downward load into the seam and on into the roof's own clips and purlins, so the roof manufacturer's approval of the clamp and a check of those clips both still apply. MCRMA lists GD22, Installing renewables on metal roofs: a checklist, and a guidance document on industry warranties, GD02, among its publications.
What changes on insulated composite panel roofs?
A composite panel has an insulating core between metal skins, so fixings cannot rely on the core. K2 says its solar fasteners let the mounting system be fixed in the steel or wooden substructure on trapezoidal sheet and sandwich panel roofs, and lists approval from the panel manufacturer as a requirement for BasicRail on sandwich panels. The German building approval K2 cites for direct screwing covers some panel makers only, so a UK project needs the panel maker's own written position.
The core also matters for fire. LPCB's LPS 1181 Part 1 sets requirements and tests for built-up cladding and sandwich panel systems used as the external envelope of buildings, and BRE offers fire testing to it, so ask for the panel's listing and test basis.
Approved Document B's FAQs say that under diagram 8.2a a combustible-core panel should incorporate a band of A2-s3, d2 material 300 mm wide centred over a compartment wall, while low-rise residential, office or assembly buildings fall under diagram 8.2b with different rules. Where an array sits near a compartment wall, the panel construction at that junction is part of the fire design, so ask the designer to show it. For the array itself, insurers read RC62; the RC62 guide sets out the separations.
How are rooflights and fragile surfaces handled?
HSE says all roofs, once fixed, should be treated as fragile until a competent person has confirmed they are not. Rooflights in the roof plane can be hard to see in some light or when painted over, and non-reinforced fibre-cement sheets are likely to be fragile. HSE puts falls through fragile surfaces, particularly fibre-cement roofs and rooflights, at 22% of fatal falls from height in construction.
Its order of control is avoidance first, such as working from below on a platform, then stagings, guard rails, fall restraint, fall arrest and nets, then warning notices on the approach.
The Advisory Committee for Roofsafety (ACR) publishes the Orange Book for work on profiled sheeted roofs and the Green Book for fragile roofs, and MCRMA publishes a non-fragility checklist. MCRMA also notes that designing for safety covers people involved in the installation of PVs, inspections and repair. A rooflight map on the drawing, walkways that stay clear for later work and the CDM duties in the CDM client guide belong in the design, and maintenance depends on them.
What should be agreed with the roof manufacturer and shown in the fixing pack?
- Sheet profile, gauge, crest width and condition, with fixing positions against purlins.
- Proof-test results for existing fasteners where there is doubt.
- The clamp or fixing matched to the seam or profile, which one the roof manufacturer accepts and who may fit it.
- How each penetration is sealed; K2 and Enstall both supply seals with their screwed fixings.
- The roof manufacturer's written approval and, for composite panels, the panel maker's, plus how the existing roof warranty is treated.
- Wind and snow load calculations by an engineer, covering purlins and sheet fixings.
- A rooflight map and fall protection plan.
Who answers for a later leak should be settled in writing too: NFRC lists disputes between trades over responsibility among the consequences when roof and PV work are not coordinated.
The wider sequence is in the commercial PV installations guide, and warehouse and industrial roofs are covered on the warehouses and industrial units page. Low-slope membrane roofs use different methods, in flat roof mounting, as do tiled roofs, in pitched roof mounting. Roof details can be sent through the site's enquiry form.
Sources
- K2 Systems product catalogue: MiniRail, MultiRail, BasicRail, SingleRail and SolidRail, checked 22 October 2026.
- Enstall: ClickFit Evo Steel Roof and Standing Seam Roof, checked 22 October 2026.
- MCRMA: wind loading guidance, roof safety, guidance documents and advice notes, checked 22 October 2026.
- Fragile surfaces, Health and Safety Executive, checked 22 October 2026.
- Loss Prevention Standards, LPCB RedBook Live, and fire testing, BRE Group, checked 22 October 2026.
- Approved Document B: frequently asked questions, MHCLG and Building Safety Regulator, last updated 21 February 2025, checked 22 October 2026.
- S-5! standing seam clamps, S-5!, and NFRC's end-of-life roofs case study (26 March 2026), checked 22 October 2026.
Common questions
Does a standing seam roof need any holes for PV?
Not for the clamps. Seam clamps grip the seam instead of penetrating the sheet, and S-5! describes its standing seam clamps as non-penetrating. Clamps are matched to the seam profile, cable routes and other equipment are separate questions, and the roof manufacturer should still approve the clamp.
Can PV rails be fixed to an insulated composite panel roof?
Yes, with the right fixing and approval. K2 fixes through to the steel or wooden substructure and requires the panel maker's approval for BasicRail on sandwich panels. Enstall lists sandwich roofs for its screwed profiles. The panel maker's written position comes first.
Why does sheet gauge matter?
Screwed fixings only hold if the sheet is sound. K2 states minimum thicknesses of 0.4 mm for steel and 0.5 mm for aluminium, plus a minimum crest width, for its BasicRail. Corroded or thin sheet can fail those minimums, which is why a survey records gauge and condition.
Who checks that the purlins can take the array?
A structural engineer. MCRMA says wind loading must be calculated for every building by a qualified engineer or suitable software in experienced hands. The array adds loads the roof was not designed for, so purlins and fixings are checked as well as the rails.