The short answer
A barn roof replacement starts with the frame: sound purlins and rafters can take a new covering, while rotten or bent timbers need repair first. The covering is then chosen for how the building is used, usually coated metal sheets, fibre-cement or insulated composite panels. Roof area, access equipment and the number of rooflights usually decide the price. Listed barns and those in a conservation area need consent checks first.
What is a barn roof actually made of?
Barns around Swindon and the Vale fall into a few families. Timber-framed barns of the old type have clay or stone slate, or pantiles, on battens across heavy rafters. Farm buildings put up after the war often carry corrugated sheeting on steel or timber purlins, which are the horizontal beams that hold the sheets. Modern portal-frame sheds hold insulated profiled metal or composite panels on steel rails.
Each family fails in its own way. Old slate loosens where nails rust and slates slip. Cement sheeting turns brittle and cracks along the laps. Metal sheets corrode at fixings and cut edges, which our page on sheet corrosion explains. Knowing which family you own tells the surveyor what to look for.
Does the frame need work before the new covering goes on?
Quite often. Years of small leaks soak timber at the wall plates and the lower ends of rafters, and nests, feed stores and animal moisture add to it. A survey from inside the barn and from the roof itself looks for sagging ridges, spread walls, soft rafter feet and insect damage.
Repairing a rafter foot or replacing a wall plate is routine work. A frame that has moved badly is a different conversation, and a structural engineer may be asked to advise. What the new covering weighs also counts. Stone or clay is heavy, whereas lightweight sheets put far less load on the frame, though they behave very differently in wind and in noise. Settle the frame question first and the covering second.
Have the surveyor photograph the roof from inside the barn looking up, as well as from outside. Staining on boards, daylight through laps and white salt marks on timber all tell a story that the outside of the roof hides.
Which covering suits which barn?
For a working agricultural building the usual choices are coated profiled steel, insulated composite panels and, in some cases, fibre-cement. Steel sheets are light and quick to lay, and a coating protects the cut edges. Composite panels bring insulation, which suits barns holding livestock, temperature-sensitive machinery or stored produce that must stay dry. Our page on composite roof panels compares the build-up.
For a period barn that has been converted, or stands in a village, the right answer may be to keep clay tiles or stone slate. A change of covering alters how the building looks, and councils take an interest. Condensation is the other trap. A warm, damp interior under an uninsulated metal sheet drips like a leak even when the roof is sound.
Rooflights are worth deciding at this stage. A barn used for storage may need very little, whereas a workshop or packing area benefits from steady daylight. Roof windows should be sized and spaced so each sheet and lap stays supported, and each one needs flashing detail around it.
Do you need permission to reroof a barn?
Putting back the same material seldom needs a planning application; to the eye the barn stays as it was. That changes if the barn is listed, if it stands in a conservation area with an Article 4 direction, or if the new material looks different. Ask Swindon Borough Council's planning team, or whichever council covers your barn.
Building Regulations are a separate test. Under Planning Portal guidance, building control approval is not usually required if under 25 per cent of the total building envelope and under 50 per cent of the roof is touched. A barn being converted to a new use is a different case altogether. Should the job be notifiable, that paperwork is part of what we do.
Bats and nesting birds use old barns, and both are protected. If you know a barn has roosts or nests, mention it at the start so the work can be planned properly.
What moves the cost of a barn roof?
Roof area comes first, then height and access. A long, low barn can often be reached from a mobile platform, whereas a tall one needs scaffold or edge protection. MyBuilder quotes around £850 to £1,200 for scaffolding on a standard two-storey house, and a large farm building costs more. The covering, the amount of timber repair, the number of rooflights and the disposal of old sheets all move the total.
If old sheets prove to be asbestos cement, handling and disposal follow separate rules, covered on our page about asbestos on commercial roofs. Our photographs show the frame and the covering, and a written quote follows. Before comparing totals, see whether VAT and scaffold sit inside each figure.
Disposal of old sheets and timber, skip hire and the tidy-up at the end all belong in the total. We leave the yard clear and carry the waste off.
Rooflights, solar and the next twenty years
A reroof is the easiest moment to think about the future. Rooflights bring daylight into a barn that is used as a workshop or store, and panels for solar on the south slope are easier to plan when the frame is open. Our page on solar panels on a commercial roof explains what the structure and covering need to be like first.
Choose a covering whose life matches your plans for the building. For wider background on every system and service we handle, start from our commercial roofing hub.