Rafter, purlin & roof timber repair
In short
Where a leak has run long enough to reach the structure, the rotted rafter ends or purlin sections get cut out and spliced or sistered with new treated timber. A visibly sagging or dipped roof is structural and gets looked at properly before anything is re-covered over the top of it.
Also called: Rotten rafters · Roof timber repair · Sagging roof · Purlin repair
Signs you need this
- A visible dip, sag or bow in the roof line
- Timber in the loft that is dark, soft or crumbling
- Rotted rafter ends visible from inside the eaves or behind the fascia
- A ridge line that has dropped noticeably at one end
- Walls bowing outwards at first-floor or eaves level
- Cracked plaster following the line of a ceiling or a wall head
Roof timber is the last thing to fail and the most expensive, which is the whole argument for dealing with leaks early. Water that gets past the covering soaks the batten first, then the underlay, then the rafter beneath — and by the time it has reached the rafter it has usually been going on for years.
Rafter feet are where it shows first. The bottom end of a rafter sits at the eaves, which is the wettest, coldest, least ventilated part of the roof, and it is directly behind the gutter. An overflowing gutter left for a few winters rots rafter ends and the wall plate they sit on, and that repair is considerably more involved than the gutter clearance that would have prevented it.
The repair itself depends on how much has gone. A short rotted length is cut back to sound timber and spliced, or a new section is sistered alongside the original and bolted through so the load transfers into good wood. Where a purlin has sagged, it may want propping and a new member alongside. Where the damage is extensive, the honest answer is a structural engineer rather than a roofer with an opinion.
A sagging roof line is worth understanding rather than panicking about. Many old roofs have a gentle dip that has been there for a century and is doing no harm — a slate roof settles, and Victorian carpenters were working to what the timber gave them. What matters is whether it is moving. A dip that has always been there is a characteristic; a dip that has appeared or worsened in a couple of years is a structural problem.
Spreading is the other classic. A pitched roof pushes outwards at the eaves, and if the ties that resist that have been cut — usually to make a loft conversion, sometimes decades ago by somebody who did not think it mattered — the roof spreads, the walls bow, and the ridge drops. That has to be resolved structurally before any new covering goes on, because a new covering on a spreading roof is a lot of money spent on a moving target.
Woodworm and rot get confused, and they are different problems. Active rot needs the moisture stopped and the timber replaced. Old woodworm flight holes in dry timber, with no frass and no live activity, are historic and generally need nothing at all — which is a conversation worth having before somebody sells a treatment for a beetle that left in 1974.
What the job covers
- Full inspection of the roof structure from within the loft
- Rot traced back to its source — the leak gets fixed first
- Rotted sections cut out and spliced or sistered in treated timber
- Wall plate and rafter feet checked at the eaves
- An honest call on when a structural engineer is needed instead
- No re-covering over a structure that has not been resolved
What it costs
We don't publish a price for this yet, because a number pulled out of the air is worse than no number at all — your roofer has to honour it. On roofing it would also be close to meaningless: access is often the biggest single factor, and it varies enormously house to house. You'll get a firm price for your actual job when they ring you back, before any work starts. The quote itself is free and there's no obligation either way.
Common questions
My roof has a dip in it. Is that serious?
Often not. Plenty of old roofs have carried a gentle sag for a century with no consequence at all — settlement in a Victorian roof is normal. What matters is movement: a dip that is the same as it was in the photographs from ten years ago is a characteristic, and one that has appeared or deepened recently is a structural question worth answering properly.
Do I need a structural engineer?
For localised rot in a rafter foot, no — that is a carpentry repair. For a roof that is spreading, a purlin that has deflected, or anything where the walls are moving, yes. A roofer who tells you plainly that this one is beyond them is doing you a favour; the alternative is a new roof laid over a problem that is still moving.
Should I treat woodworm I have found?
Only if it is active. Old flight holes in dry, sound timber with no fresh frass are historic and usually need nothing. Beetle activity depends on moisture, so the far more useful step is normally to fix whatever is keeping the timber damp. Be wary of a survey that recommends whole-roof treatment on the strength of some holes.
Can the covering go back on while the timbers are being done?
The structure gets resolved first, always. Re-covering a roof whose timbers are still moving or still wet wastes the covering and hides the evidence. Where the roof has to stay watertight in the meantime, that is what temporary sheeting is for.
Need this doing in Macclesfield?
Tell us the job and it goes straight to our local roofer — one call back, usually the same day. Free quote, no obligation.