Rotten Window Sill Repair in Wellington
Window and Glass Repair Wellington repairs rotten window sills, bottom rails and jamb ends in timber joinery across the city. We cut the soft timber back to sound wood, let in new timber shaped to the original profile, glue and pin it, and prime it ready for paint. The rest of the window stays where it is.
- Soft timber cut back to solid and new timber scarfed in
- Profiles matched so the repair disappears under paint
- Far cheaper than replacing the joinery
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Timber windows in Wellington rot from the bottom up, and always for the same reason. The paint film cracks, driving rain gets behind it, and the end grain in the sill soaks it up and holds it. South and west facing elevations go first because that is where the weather comes from. The head and the stiles of the same window are usually still perfect old growth rimu or matai, which is exactly why replacing the whole thing is a waste.
Finding the full extent before quoting
Rot spreads further than it looks. Paint holds a shell over timber that has gone soft behind it, so a patch that appears to be 100mm across is often twice that. We probe with an awl along the whole sill and up the jambs before we quote, so the price does not move once we open it up.
Scarf repair instead of filler
Two part filler over soft timber is a cosmetic fix that lasts a season or two. It is harder than the wood around it, so it works loose as the timber moves, and it seals moisture in behind itself.
A scarf repair cuts a clean angled joint back into sound timber and lets in a new piece of seasoned wood, glued with an exterior adhesive and pinned. Shaped and primed, it disappears under paint and lasts as long as the rest of the window.
Stopping it happening again
The repair only holds if the water stops getting in. That means end grain sealed before priming, a proper drip groove under the sill nose so water cannot track back, and paint maintained instead of left until it cracks.
On exposed southerly elevations we will usually recommend recutting the drip groove if it has been painted solid, which is a very common cause of repeat rot.
Making sure it does not come back
The drip groove
Under the nose of a timber sill there is a groove that makes water drop off rather than track back underneath. Decades of repainting fill it, and once it is bridged every drop of water runs back into the joint between sill and frame.
We recut it as part of every sill repair. It is a five minute job and it is the single most common reason a sill that was repaired properly rots again in the same place.
Sealing end grain before priming
Timber takes on water through its end grain many times faster than through its face. A scarf repair creates fresh end grain at both ends of the new piece.
Those faces get sealed before the piece goes in, then the whole repair is primed. Skipping that step is invisible on the day and obvious in three winters.
Rotten Window Sill Repair at a glance
- Method
- Scarf repair into sound timber, glued and pinned
- Timber
- Seasoned exterior grade, profiled to match the original
- Not used
- Two part filler over soft timber as a structural repair
- Detail
- End grain sealed, drip groove recut where it has been painted over
- Finish
- Primed and ready for topcoat, or fully painted on request
- Full sill
- Complete sill replacement into the existing frame where needed
Rotten Window Sill Repair in Wellington: common questions
Can a rotten window sill be repaired, or does the window need replacing?
Repaired, in the large majority of cases. The rot sits at the bottom while the rest of the frame is sound. A scarf repair costs a fraction of new joinery.
Is filler good enough?
Not on its own over soft timber. It traps moisture and works loose. New timber let into a clean joint is the repair that lasts.
Why does the same window keep rotting?
Usually a drip groove that has been painted solid, so water tracks back under the sill instead of dropping off. We recut it as part of the repair.
Recent Wellington jobs
Got three quotes for retrofitting the front of the house. Only ones who measured every opening and explained why the north facing rooms needed different glass. Eleven windows over two days, and the road noise dropped more than I expected.
Landlord here. Had four properties assessed for the Healthy Homes ventilation rule and two needed openable sashes freed up rather than new joinery, which saved me a fortune. Straight answers, written report, no upselling.
Ranch slider had been jamming for years and we assumed it needed replacing. Turned out to be rollers and a bent track. Two hours, a fraction of the price we were braced for.
Fogged unit in the lounge, measured on the Tuesday and in by the following Monday. Fair price and they cleaned up after themselves.
Get a price for rotten window sill repair in Wellington
Free measure, fixed written quote, and a straight answer on whether it needs repairing or replacing.
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Four questions and you are done.