The short answer
Yes. Roofers repair and replace rafters, the timbers that slope from ridge to wall and hold up the battens, when they are rotten, split or damaged. A short stretch can be strengthened by fixing a new timber alongside, called sistering, while a failed one is cut out and replaced. Work that alters the way the roof carries weight needs a structural check and may need building control.
Rafters sit hidden under the covering, so owners usually meet the question when a surveyor or roofer finds a problem. Here is what gets done and who decides.
How a damaged rafter is dealt with
A rafter slopes from the ridge, where the two sides of the roof meet, down to the wall plate, a timber bedded on the wall head. Battens nail across the rafters and the covering hangs from the battens. When a rafter is soft or cracked, the slope above can dip, so the fix has to restore its strength.
What is sistering?
Sistering means bolting or screwing a new timber of the same depth beside the weak one, so the pair work together. It suits a rafter that is sound for most of its length but damaged at one end, or one that has cracked without rotting through. A badly rotten rafter is cut out and replaced with a new length, jointed into the ridge board and wall plate.
Which route is right depends on what the timber looks like once it is exposed, not on a guess from the loft. We look at the damaged section, take pictures and show you before the work is agreed. Wet rot and beetle usually have a cause, such as a leaking valley, failed lead around a chimney or a blocked gutter, and mending the timber without mending the cause only postpones the next repair.
When a structural engineer is needed
A roofer can judge plenty of timber repairs from experience. Some jobs go beyond that, and an engineer has to calculate the loads and design the fix.
Which rafter jobs need an engineer?
Cutting out several rafters together, removing a purlin, a chimney breast or a wall that holds the roof up, changing the roof shape, or putting on a heavier covering all change how the load travels. Where a new covering adds weight, the Planning Portal recommends an engineer's or surveyor's opinion first. A ridge that sags or a slope that bows is another prompt for that call, rather than propping it up by trial and error.
A written engineer's detail also gives your building control body, and any future buyer, something to read. Not sure what you are looking at? The answer on a sagging roof explains the signs, and the work usually begins with a loft inspection and photographs. A structural fault is never a place for guessing. When timber needs a designer's eye, the survey tells you so before a price is given.
Building control and structural work
Structural work on a roof falls under the Building Regulations. Structural alterations are on Somerset Building Control's own list of work needing an application, and a registered building control approver can handle it instead.
Does replacing a rafter need approval?
It depends on the scope, and your building control body is the one to ask. For a re-roof, the Planning Portal sets the national test: normally no application is required while under 25 per cent of the total building envelope and under 50 per cent of the roof is touched. Somerset Building Control publishes no separate figure, so that test is the guide. Strengthening or replacing structural timbers is a different thing from swapping a covering, so ask before starting, not afterwards.
Somerset Building Control answers on 0300 303 7790. Where work was done without approval, regularisation can be sought if it was carried out after 11 November 1985. A completion certificate gives you the paper that a buyer's solicitor asks for. Keep any engineer's drawing, the timber receipt and the certificate together with your house papers.
What decides cost and what happens next
Rafter work varies more than almost any other roof repair. A single end repair under a slipped valley is a small job. A run of rotten rafters beneath a leaking chimney flashing may mean stripping the slope, replacing timber, fitting new battens and underlay and recovering it, with scaffold standing for the length of the job.
Will repairing a rafter mean re-roofing?
Sometimes, since the tiles must be stripped before the timber can be reached. When the covering is sound, reusing roof tiles explains how they can go back on. If the battens are failing as well, the answer on whether roof battens need replacing lists the signs. Cost follows the number of rafters, how hard the slope is to reach, the type of covering and what the exposed timber turns out to be.
The pitched roofing page sets out our wider work. A survey comes first: we inspect the roof and the loft, you see photos of the timber, and one written price follows. Where an engineer is needed, that comes up at the survey, well before work starts.
More on rafter repairs
Can rotten rafter ends be mended without a new roof?
Often, yes. The covering is lifted over the damaged area, the rafter end is cut back to sound timber and a new section is spliced or sistered in, then the covering is relaid. Where the rot is widespread, the slope may be better stripped and rebuilt, and the survey shows which applies.
How do I know if a rafter is damaged?
Signs include a dipping roof line, a wavy slope, daylight or damp patches in the loft, and timber that feels soft when pressed with a screwdriver. A look in the loft with a torch, from the joists, is a start. A roofer can inspect the whole run, including parts you cannot reach.
The full picture: Pitched roofing in Taunton ยท More short answers