Barn Roof Types and Solar: Steel, Fibre-Cement & Slate

Your roof covering decides the install

When people ask whether their barn can take solar, they usually mean will it fit and will it pay — but the first question an installer actually asks is what is the roof made of. The covering on a barn roof dictates the mounting system, the fixings, the structural check, and in some cases whether panels can go up at all before other work is done. A modern profiled-steel shed and a corrugated-asbestos cattle court might look similar from the yard, but they sit at opposite ends of the solar-readiness scale.

This guide runs through the four roof coverings you meet on British barns — profiled steel, fibre-cement, asbestos cement, and traditional slate or clay — and explains the fixings, the pitfalls and the right route for each. Get the covering right and the rest of the design follows easily.

Profiled steel: the ideal canvas

If your barn wears profiled box-profile steel, you have close to the perfect solar roof. This is the standard cladding on most modern agricultural buildings — the steel-frame portal barns that dominate the working farm — and it was practically made for PV.

• Standard clamps, fast install. Panels fix to the raised profiles using purpose-made clamps or short rails that bolt or self-drill straight into the sheet ribs. There is a mature, off-the-shelf mounting kit for every common profile, so installation is quick and clean.
• No valleys, dormers or shading. A portal-frame roof is a single clear span — one large, simple plane facing one way. That means a high-yielding, easily wired array with no obstructions to design around.
• A frame built for load. Steel portal frames are engineered for snow and wind, so they almost always carry the modest PV dead load (around 10–15 kg/m²) on a simple structural sign-off. We still confirm purlin spacing and frame capacity, but on a modern shed it is usually a formality.

This is the roof type where the only real decision is how big to go — and on a working barn you size to the load, because the roof itself is rarely the limit. Around 7–8 m² of clear roof carries a kilowatt of panels, and most portal sheds offer far more than they need.

Fibre-cement: workable, but check the condition

Many barns from the 1980s and 1990s onward are roofed in modern fibre-cement sheeting — a cement-based corrugated sheet made without asbestos. It is a perfectly good roof for solar, but it behaves differently from steel and the condition matters.

• Hook bolts, not clamps. Fibre-cement is typically fixed with hook bolts that pass through the sheet and grip the purlin beneath, with weather seals at every penetration. The mounting frame hangs off these rather than clamping to a steel rib.
• Condition is the key check. Fibre-cement gets brittle and can grow moss and surface degradation with age. Before any array goes up we survey the sheets for cracking, delamination and fixing corrosion. A sound fibre-cement roof takes panels well; a tired one may need sheets replaced first.
• Mind the foot traffic. These sheets are walked on with crawler boards and roof ladders during install — never directly — because a brittle sheet can give way. This is a normal part of a careful install, not a reason to avoid the roof.

Fibre-cement appears across steel-frame portal barns and older livestock buildings alike, and a well-maintained fibre-cement roof is a straightforward solar job.

Asbestos cement: you cannot load it

Here is the one that stops a lot of projects in their tracks. A great many barns built before 2000 are roofed in asbestos cement — and it is essential to be clear about this: asbestos cement cannot be drilled, loaded or fixed to for solar.

• Why not. Disturbing asbestos cement releases fibres, and the sheet was never engineered to carry the point loads of a mounting system in any case. Drilling a hook bolt through it is both a health hazard and a structural non-starter.
• The law. Under the Control of Asbestos Regulations 2012 (CAR 2012), work that disturbs asbestos cement must be carried out by a competent contractor following the regulations, with safe handling and licensed disposal. This is not a job for the farm team or a general roofer.
• The proven route: strip-and-reclad, then PV. The standard, sensible answer is a combined project — licensed removal of the asbestos cement, re-cladding to modern profiled steel, and then the solar array on the new roof. The advantage is real: the solar business case often part-funds a re-roof you were going to need anyway, so a long-deferred asbestos problem and an energy upgrade get solved in a single project rather than two.

If your barn has the tell-tale grey corrugated sheets of a pre-2000 build, assume asbestos cement until a survey says otherwise, and read our dedicated guide to solar on an asbestos barn roof before planning anything.

Slate and clay tile: heritage roofs

On older barns — particularly traditional and listed barns such as stone threshing barns and field barns — the covering is often natural slate, stone slate or clay tile on a timber structure. These roofs can take solar, but the constraints are heritage and fabric rather than load.

• Heritage controls come first. If the barn is listed, permitted development is removed and you will need Listed Building Consent and usually planning permission; conservation areas, National Parks, AONBs and the Broads bring tighter controls even on unlisted barns. The design then has to be sensitive — discreet siting on a secondary or rear slope, low-profile in-plane mounting, all-black modules.
• Fragile and tired battens. Old slate and clay can be brittle, and the battens and timbers beneath may be at the end of their life. A roof survey precedes any design, and a failing roof may need attention first.
• Reversible fixings. On a historic roof, mounting that goes into structural timbers, reuses existing penetrations and can later be removed without trace is the approach conservation officers respect.

Where a heritage roof genuinely cannot carry an array, a ground-mount system nearby is the fallback that keeps the building untouched.

Find out what your roof is wearing

Steel says size it up; fibre-cement says survey the condition; asbestos cement says strip, reclad, then solar; slate and clay say heritage design first. The single most useful thing you can do before getting quotes is establish, honestly, what your barn roof is made of — because that one fact shapes the fixings, the cost and the timeline of the whole job.

If you are not certain what your roof covering is, or you want it assessed properly, request a quote and we will survey the roof, confirm the structure and tell you exactly which route your barn needs — including whether a re-roof should come first.