Composite roof panels on industrial buildings
Updated 23 October 2026 · SEO Dons Editorial
Insulated metal panels have been used on industrial and commercial buildings for over 40 years, according to the trade body EPIC. This guide covers how they differ from built-up roofs, lifespan, defects, insurer questions and repair routes. Sheet roofs have their own fixings and lap seals guide, and the wider choice sits in the industrial roof refurbishment guide.
What is a composite roof panel, and how is it different from a built-up roof?
MCRMA describes sandwich panels, also called composite panels, as factory-produced roofing and wall cladding assemblies: an inner and an outer metal sheet bonded to an insulation core, predominantly polyisocyanurate (PIR). A built-up roof is assembled differently, from metal inner and outer profiles held apart by a support system installed on site, with mineral fibre insulation between them.
The difference moves the weak points. MCRMA's 1995 design guide says a rigid foam panel's faces are impermeable and its core fills the panel, so interstitial condensation cannot occur within a panel; the risk shifts to the joints between panels.
Do insulated roof panels work?
Yes, when they are specified, installed and kept in repair as a system. BSI describes BS EN 14509 as specifying requirements for factory-made, self-supporting, double skin metal-faced insulating sandwich panels, and MCRMA says long panels reduce the number of end laps and so the potential leak locations. The caveat is that a product standard covers the panel as made, not the roof as built. MCRMA's installation guide says panels need their full complement of fasteners fixed as work proceeds, because partial fixing leaves the installation short of the non-fragility category expected. A good product can make a poor roof; the evidence sits in the laps, fixings and sealant.
How long do composite roof panels last?
No source used for this page gives a single service life for an installed insulated panel roof, so this page does not invent one. MCRMA's durability guidance (GD39 section 7, 8 January 2022) says sandwich panels designed and installed as the manufacturer recommends will generally have the durability of the metal they are made from. The finish is where published numbers sit. MCRMA's steel guidance (GD39 section 5, 6 June 2022) says BBA certificates indicate a minimum appearance life, usually the period before first maintenance painting, which is less than the coating's design life against corrosion; typical lives differ by colour and manufacturer and depend on location, aspect and use.
Surroundings matter: MCRMA says salt atmospheres and industrial pollution such as sulphur dioxide harm materials and coatings. An older MCRMA paper from 1995, kept online for reference only, put manufacturers' quotes for coating durability at 10 to 25 years, normally for the coated areas rather than the cut edges, which deteriorate more quickly. Read that as history, not a forecast. The same paper said the building should be inspected annually, with debris removed and panels cleaned; see the gutter cleaning and roof cleaning guides.
What goes wrong with composite roof panels?
Most defects trace to a short list of checkable details.
| Fault | What the sources say |
|---|---|
| Leaking end laps | Three runs of butyl sealant, one either side of the fastener line and one within 15 mm of the exposed end, with fasteners through the external skin of both panels (MCRMA installation guide). |
| Leaking side laps | Stitched with self-drilling fixings at the maker's centres, typically 450 mm, with the seal on the weatherside. |
| Fasteners | From a source the maker recommends, carbon or austenitic stainless steel depending on warranty conditions; not under or over tightened if the washer is to seal (1995 paper). |
| Cut edges and scratches | Site-cut edges are more susceptible to corrosion, deep scratches through the paint can lead to premature corrosion, and panels should be cut with saws, not abrasive wheels (1995 paper). See the cut edge corrosion guide. |
| Skins separating, core exposed | The government's fire risk guide says to check that the skins adhere tightly to the core and that openings for cables and ducts are sealed so the core is not exposed. |
| Cold bridging and condensation | MCRMA's checklist asks for side laps to be fully butted, and supported end laps sealed to the purlin, to limit cold bridging and condensation. |
| Impact damage and penetrations | Coating damage must be repaired to prevent premature corrosion, and penetrations integrated to avoid ponding and leaks (1995 paper). |
Much of this shows from inside the building before anyone goes onto the roof. MCRMA's non-fragility checklist says to assess the roof from the inside first, and to treat it as fragile if:
- fasteners are missing or not attached to the purlins;
- there are fewer than three fasteners per sheet or panel width at each bearing end;
- corrosion is visible on the liner or inside face of the panel; or
- liner or sandwich panel joints are not in close contact with the purlins.
These are safety items as well as defects. MCRMA says end and side lap seals form part of the assembly, and the ACR's Orange Book says a failed component makes the assembly likely to become fragile. The fragile roofs and rooflights guide covers the owner's duties.
What do insurers ask about the core of an insulated panel?
Fire guidance and insurance certification both focus on the core, because cores differ widely. A 2006 government fire risk assessment guide for factories and warehouses says differing fire hazards are associated with common types of insulation, that the core is difficult to identify once installed, and that mineral fibre cores have less potential for fire development than polymeric cores.
EPIC, the trade association for the PIR-cored panel industry, says that from 2004 all its members' panel systems have PIR cores meeting LPS 1181 or FM 4880/4771 Class 1 certification. It says LPCB and FM Global approved PIR panels are generally acceptable to insurers, and relays the Association of British Insurers' view that non-certificated panels have a role in low and medium risk external envelopes, particularly PUR panels on existing buildings. That is one side's summary; insurers set their own terms, so ask in writing.
Cores are hard to access and all PIR cores look alike, so EPIC stresses keeping the literature supplied with the panels. Worth assembling:
- the maker, product name and installation date;
- any LPCB or FM certificate, and the grade or class it states;
- a record of damage, repairs and openings that expose the core;
- the fire risk assessment, which the government guide says may need revising where combustible panels are used in areas with a high life risk.
Repair, over-roof or replace: which route fits?
| Finding | Usual route | Points the sources raise |
|---|---|---|
| Isolated lap or fixing leaks; skins and core sound | Re-seal and re-fix to the maker's details | MCRMA's sealant and stitching details are the benchmark |
| Coating breakdown or cut-edge rust, no perforation | Local treatment | See the cut edge corrosion guide |
| One or a few damaged panels | Replace the panels | The 1995 paper says replacing a damaged outer section generally means removing the entire panel, and the new one may not match the weathered colour |
| Widespread leaks or failing skins on a sound structure | Over-roof | MCRMA says over-roofs can go over composite panel systems; the existing roof and rooflights must be non-fragile as the working platform; Building Regulations and a planning application are likely to be required |
| Wet or separated core, or a core that must come out | New panels | EPIC says panels have been used extensively in refurbishment for over 30 years; its end-of-life guide treats panels made with ozone-depleting blowing agents separately, so identify the panel type before strip-out |
On an over-roof, MCRMA does not recommend fixing new spacers into the purlins through the old ones, because that assumes the old spacers are adequately secured, which may not be the case as they are not visible. It recommends a top hat cleat fixed into the existing purlins. The over-sheeting page covers the method.
Whatever the route, the survey should record what the panels are: maker, core, fixings, laps and penetrations. LRWA lists single skin, twin skin or composite panel among the things to establish before detailing, and new panels or a new outer skin change the vapour picture explained in the metal roof condensation guide. If you want contractors to price a repair, an over-roof and new panels against one survey, you can send an enquiry through the site's form, and the industrial roof refurbishment page compares the options.
Sources
- MCRMA, GD17 (2019), GD23 (2020), GD13 (2020), GD38 (2022), GD39 section 4, section 5 and section 7 (2022), Technical Paper 9 (1995, archived) (MCRMA, checked 22 October 2026)
- Fire safety risk assessment: factories and warehouses (Home Office on GOV.UK, checked 22 October 2026)
- EPIC, about, fire performance, certificated panels, refurbishment, end of life, identification guide (EPIC, checked 22 October 2026)
- BS EN 14509:2013 (BSI, checked 22 October 2026)
- The Orange Book (Advisory Committee for Roofsafety, checked 22 October 2026)
- Guidance Note 10 (LRWA, checked 22 October 2026)
Common questions
Can you walk on composite roof panels?
Not on the assumption that they are safe. MCRMA's checklist says a roof should be declared fragile unless documentation confirms its current non-fragility, although tested systems installed to the maker's instructions can provide a sound platform for work, with netting, edge protection and safety lines.
Are composite roof panels the same as rainscreen composite panels?
No. EPIC says metal-faced, PIR core composite panels must not be confused with rainscreen cladding composite panels, and its identification guide covers only panels with steel or aluminium facings.
How can an owner find out what is inside the panels?
Mostly from paperwork. The government's guide says the core is difficult to identify once installed, and EPIC says the literature supplied with the panels matters; it adds that small samples can be sent to a laboratory when the blowing agent is unclear.