Roof timbers
Do roof timbers need replacing when you re-roof?
The short answer
Not always. A re-roof strips the covering and exposes the timbers underneath, and what happens next depends on what the survey and the strip-out show. Battens are normally renewed with the new covering. Rafters, purlins and the wall plate stay if they are sound and are repaired or replaced only where they are rotten, split or have moved. Sound timber is kept, which keeps the job smaller.
How we judge the timbers under a roof, which ones usually go and which stay, and how a structural repair changes the paperwork.
Which timbers sit under the covering
A pitched roof is a frame. The rafters are the sloping timbers that span from the apex to the lower edge and carry each slope. Purlins are the horizontal beams that hold up the middle of the rafters, and the wall plate is the length of timber laid on the head of the wall where the rafter feet rest. Across the rafters lie the battens, the thin strips that the tiles or slates are hooked or nailed to, and beneath them is the underlay, the sheet that catches whatever gets past the covering.
Of all these, the battens and underlay are the parts that normally come off with the old covering and are replaced with the new one. The frame is different. It was built to last as long as the house, so the question on a re-roof is not whether to renew it but whether it has been damaged, and by what.
The timber check comes first in the job, before a single new batten is ordered, because what it finds decides how much of the frame is touched.
What we look for in the loft and on the strip-out
The survey starts inside the house. Up in the roof space we look over every rafter and the boarding above for dark staining, feel for soft or crumbling wood at the rafter feet, and sight along each slope for sagging between supports. A dip can mean a timber has failed, but it can also mean old, heavy tiles have been bending perfectly sound timber for decades.
Some of it only shows once the covering is off. Rot settles into the spots where moisture has been entering over a long period: around chimneys, along valleys, beneath failing gutters and at the wall plate. Insect damage and wet rot look different, and pressing a bradawl into the wood tells you quickly whether it is sound. Timber that is only stained by a leak fixed long ago is often perfectly good.
Each find gets a picture, which lets you inspect the very same wood before anybody signs off on extra work.
When a timber is repaired, sistered or replaced
The smallest cure that properly works is the one we choose. A rafter with a rotten foot can often be repaired by cutting out the bad section and bolting a new length alongside it, which carpenters call sistering. A short run of damaged boarding or a single batten is simply swapped. Swapping a whole rafter or purlin is reserved for cases where the damage runs through its depth or the timber is cracked across.
Moisture is behind most timber damage, so the repair has to deal with the leak as well as the wood. Fixing one without the other only sets the clock running again. New timber fixed under a covering that is still letting water in will go the same way as the old.
Timber that has rotted because of a long-running leak is also the usual reason a repair turns into a replacement. Our guide to when to replace a roof explains where that line falls, and the main roof replacement page sets out the whole job.
Structural repairs and Building Regulations
Replacing battens is part of re-covering. Altering the structure is different. The Planning Portal names structural alterations as one reason a re-roof needs a building control application, even when the area thresholds would not otherwise apply. A new rafter, a replaced purlin or strengthening for a heavier covering all point that way.
The weight of the new covering is a related check. The Planning Portal gives an increase of 15 per cent or more as needing approval, and suggests getting a structural engineer or surveyor involved before work begins if the new covering is much lighter or heavier than the old one.
Where the work is notifiable, we explain what the building control body will ask for, and we handle the notification for you so it is not left to chance. Our page on re-roofing and Building Regulations covers the thresholds in full.
Bats, birds and what a stripped roof can reveal
Stripping a roof opens spaces that have been undisturbed for years. GOV.UK says bats and their resting places are fully protected, and lists roof replacement among the activities that may disturb a roost. If we find droppings or an occupied nest, work on that part of the roof waits until it has been dealt with properly.
The strip-out also shows how the roof was built. Older roofs sometimes have no sarking, which is the boarding or felt laid directly under the battens, and the timbers may be lighter or more widely spaced than a modern frame. That is not a defect in itself, but it changes how the new covering is fixed.
Cost follows the findings, not the other way round. Once the survey is done you get your quote on paper, as one sum for the whole job. If the strip-out shows more than the survey could see, we show you photographs and agree the next step with you before anything extra is done. Our answer on why roofing quotes vary explains what drives the difference between prices.
Related questions
Timber and re-roofing queries
Can new tiles go straight onto old battens?
It is not good practice. Old battens carry nail holes and may be thin, dry or damaged, and the new covering needs a gauge set out to suit its own tile length. Fresh battens are a small cost beside the rest of the job, so they are normally renewed along with the underlay.
Does woodworm in the rafters mean a new roof?
Not by itself. Old flight holes can come from an infestation that ended long ago. The question is whether the timber is still active and still strong enough. A specialist treatment or a timber repair may be all that is needed. A new roof is for a covering that has failed, not for a frame that can be repaired.