Rotten timber windows — diagnosed and fixed across Caerphilly
Most Caerphilly enquiries about rotten timber windows arrive with the same underlying question: whether this is a small job or the start of a big one. On the stone-fronted terraces, post-war semis around the castle and newer estates out toward Bedwas that dominate Bedwas, Trethomas, Machen, the answer usually depends on the age of the frame rather than the severity of the symptom. Locally the complicating factor is wind-driven rain off the mountain ridge, which shortens the life of exactly the components this fault attacks.
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 we typically find on survey
- The front door threshold weather-bar seal is missing its rubber blade and the metal channel is bent.
- The concrete cill under the door has heaved by 3mm across the two-metre span, tilting the whole threshold.
- The transom bar has a live crack in the plastic, opened up by summer expansion cycles.
- The internal glazing bead across the top of the bay lifts out completely with fingernail pressure.
- The internal locking cams on the multipoint have been ground down by a mismatched keep pattern.
- The georgian bar between the panes has come detached from the top spacer on one unit.
How we actually carry out the work
- Fixings are always at the reinforcement points — a screw through the chamber alone loosens within a year.
- The internal cill support is packed with hardwood the full depth of the cill, not just at the ends.
- The reveals are photographed on arrival so any pre-existing damage is on record before the crew touches them.
- Cylinders come out of the box, get numbered, and are the last thing fitted, so a lost cylinder does not stall the day.
- The letterplate brush strip is trimmed to the exact height of the door thickness so it seals without dragging.
- The manufacturer's serial-number label on the new frame is peeled off, not left to yellow on the glass for years.
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
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.
Your realistic options
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.
Where the outer frame is sound but the opening sashes are gone, new sashes into the retained frame keeps cost and disruption down.
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.
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 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
Why this comes up in Caerphilly
- Council
- Caerphilly
- Postcodes
- CF83
- Main route
- A468
- Nearest town
- Cardiff (7 mi)
Around Bedwas, Trethomas, Machen the recurring local factors are wind-driven rain off the mountain ridge; noise from the A469 corridor; tired 1990s-era double glazing failing at the seals. Commercial neighbours such as Pontygwindy Industrial Estate and Bedwas House Industrial Estate change the exposure again on the elevations that face them, and the Caerphilly County Borough Council area sets the standards any replacement work is signed off against.
- Bedwas
- Trethomas
- Machen
- Energlyn
- Llanbradach
- Abertridwr
- Rudry
- Nelson
- Ystrad Mynach
- Senghenydd
- Aber Valley
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.
Do you cover rotten timber windows across the whole of Caerphilly?
Yes — CF83 and the surrounding villages, including Bedwas, Trethomas, Machen, Energlyn. Easy in via the A469, and we're 10 minutes from the A470 for vans loaded with full-house glass.
Is rotten timber windows more common on Caerphilly properties?
It's shaped by the local stock. With stone-fronted terraces, post-war semis around the castle and newer estates out toward Bedwas, plus wind-driven rain off the mountain ridge and noise from the A469 corridor and tired 1990s-era double glazing failing at the seals, the components involved in this fault tend to age faster here than on sheltered inland new-builds.
If replacement is the answer
10-year product, 10-year foil colour, 2-year fitting
10-year product, 2-year fitting, lifetime hardware servicing
10-year product guarantee, 2-year fit warranty, lifetime hardware servicing
10-year product on every frame, 2-year fitting on the whole package, single point of contact
Other faults we see in Caerphilly
Yellowing is cosmetic and treatable; splits at the welded corners are structural and aren't.
ReadFrench doors are a pair, so the fault is usually in how the two leaves meet rather than in either leaf on its own.
ReadFog between the panes means the sealed unit has failed — the glass can usually be swapped without touching the frame.
ReadFull background on rotten timber windows
The main guide covers the mechanics of this fault in more depth, without the Caerphilly context.
Read the Rotten Timber Windows guide →Let's make your house feel more like home.
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