Diagnosis guide

Rotten Timber Windows

Rot in the bottom rail is repairable; rot that has reached the joints and the cill usually isn't worth chasing.

Most people landing here want one thing: to judge whether the timber is repairable or whether the window has reached the end of its life. That's what this page answers — no scare tactics, no automatic upsell to a full replacement.

Get it looked at 07375 533723

Flush sash window replacing rotten timber — rotten timber windows put right by Rosac

What you'll notice first

paint blistering and flaking along the bottom rail and the cill
timber that gives when you press it with a thumbnail or a screwdriver point
open joints at the corners of the sash with a dark line of moisture
putty falling away from the glass line in sections

What actually causes it

1paint film breached at a joint or knot, letting water into end grain that never dries out
2the cill drip groove painted over, so rainwater tracks back under the frame instead of dripping clear
3sealed units bedded into a timber rebate without drainage
4north-facing elevations that stay damp for months at a time

Your realistic options

Splice and repair

Sound approach on a good hardwood frame: cut back to solid timber, splice in a matched section, resin-consolidate, prime and repaint. Preserves the original look on period property.

Sash replacement in the existing frame

Where the outer frame is sound but the opening sashes are gone, new sashes into the retained frame keeps cost and disruption down.

Full replacement

When the joints, cill and outer frame are all soft, the window is past economic repair. Timber-effect uPVC or a flush-sash profile reproduces the sightlines of the original without the maintenance cycle.

Repair or replace — our honest view

Rot is one of the few faults where replacement genuinely is often the right answer — but not always, and not automatically. Localised rot in a bottom rail on an otherwise sound hardwood frame is worth repairing. Softwood frames with open joints, soft cills and thirty years of paint build-up rarely repay it.

What we check on survey

we probe the bottom rail, the cill and each corner joint rather than judging from the paintwork
we check whether the cill drip groove is still open
we look at the internal reveal for staining, which shows water has already crossed the frame
we identify hardwood versus softwood, because it changes the repair verdict

How it's priced

Splice repairs are labour-led and vary hugely with how much sound timber is left. Replacement is priced per opening. On a full elevation we'll usually price both and be plain about which one we'd choose in your position.

How urgent is it? Moderate but rising. Rot spreads along the grain and accelerates once it reaches a joint, and a rotten cill eventually lets water into the wall head and the internal plaster.

Stopping it coming back

repaint before the film breaks rather than after the timber has darkened
keep the drip groove under the cill clear of paint
clear leaves and moss out of the cill rebate every autumn

Rotten Timber Windows — questions we get asked

Can rotten window frames be repaired rather than replaced?

Yes, where the rot is localised and the joints are still tight. Resin repairs and spliced timber are perfectly durable when the underlying frame is sound.

Will uPVC look wrong on a period house?

It can, if you choose a chunky standard casement. A flush-sash profile sits flat in the frame like a timber window and, in a heritage colour, reads far closer to the original than a bulky rebated casement.

Do I need permission to replace timber windows?

In a conservation area or on a listed building, yes — and we'd tell you to check with the council before ordering anything. Outside those designations, replacement is normally permitted development.