A draughty loft rooflight has one of four causes: the sash seal has perished and no longer compresses, the timber sash has swollen or warped so it no longer closes evenly, the reveal around the frame was never insulated so it sits cold and moves cold air, or the frame has worked loose in the opening and gaps have opened at the lining. On a unit past roughly fifteen to twenty years old, all four tend to arrive together, and that is the point where resealing one part buys a season while the rest keep failing. Replacement is the fix that lasts, and it is usually cheaper over any sensible timeframe than chasing draughts around an old frame.
We do not reseal, re-gasket or patch old rooflights as a service. This page explains how to work out what has gone, so you can decide with your eyes open. The fitting detail on the replacement sits on the main pitched roof skylight installation page.
The four causes, and how to tell them apart
1. Perished sash seals
Every opening rooflight closes onto a gasket, a rubber or foam seal run around the sash that compresses against the frame to shut out air and water. That seal is a wearing part. Over fifteen to twenty years it hardens, shrinks and loses its spring, so even a sash that closes fully no longer seals. The signature is a draught you can feel with a wet finger run around the closed sash on a windy day, worst on the weather side of the house, and it is there whether or not the window is difficult to close.
On a current unit a worn gasket can sometimes be swapped, but on an older frame the gasket profile is often discontinued, the channel it sits in is degraded, and the seal is rarely the only thing gone. Fitting a new seal to a warped sash in a loose frame solves a third of the problem.
2. Warped or swollen timber sashes
Older rooflights, and plenty fitted through the 1990s and 2000s, have timber sashes. Timber in a roof takes the full range of temperature and humidity, hot in summer sun, cold and damp in winter, and over the years it moves. A sash that has swollen or warped no longer meets the frame evenly all the way round. It might close tight at the handle and stand off at the top corner, and that corner is your draught and, in driving rain, your leak.
You can see this. Close the sash and look along each edge from inside against the daylight. A bright line at one corner that closes up at the opposite corner is a warped sash. No seal, however new, closes a gap that the timber itself is holding open. This is the clearest single sign that a unit has reached the end and wants replacing rather than adjusting.
3. Uninsulated reveals: a cold line that feels like a draught
This one is not always a real draught at all. A rooflight frame sits in a gap in the roof insulation, and if that gap was never filled with an insulation collar, a continuous cold bridge runs right around the perimeter of the window. The internal reveals then sit cold, cold air sinks off them and washes down into the room, and it feels exactly like a draught even when the sash is sealing perfectly.
The tell is that it is worst in cold still weather rather than windy weather, it is even all the way round rather than coming from one edge, and the reveals may show condensation or dark mould staining. A real air draught follows the wind and comes from a gap. A cold reveal draught follows the temperature. We explain the insulation collar detail that prevents this on the flashing and collar page, and it is the same detail that causes phantom leaks, covered under water through a loft rooflight.
4. A loose frame and gaps at the lining
If the frame has worked loose in the opening, or the plaster has cracked and pulled away from the frame at the reveal, you get a direct air path from the cold roof void into the room around the outside of the frame. This often follows structural movement in an old roof, or a frame that was never packed and fixed properly when it went in. The draught here comes from the junction between plaster and frame, not from the sash.
| What you notice | Likely cause | Durable fix |
|---|---|---|
| Draught around the closed sash, worse when windy | Perished sash seal | Replace the unit if it is older; a seal alone rarely lasts on an aged frame |
| Bright line at one corner of the closed sash | Warped or swollen sash | Replacement. Timber movement cannot be sealed out |
| Cold even feeling all round, worst in still cold weather, reveals staining | Uninsulated reveal, cold bridge | Insulation collar and vapour seal, usually done as part of a replacement |
| Draught and cracking at the plaster to frame junction | Loose frame or failed lining | Refix and re-line, most often done during replacement |
Why patching an old rooflight does not last
The temptation is obvious. A new seal costs little, so why not fit one and see. The reason is that these four failures share a cause, which is age, and they arrive together. Fit a new seal and the warped sash still stands off. True the sash and the reveal is still cold. Insulate the reveal and the frame is still loose. You end up back up the ladder every winter chasing the next symptom, and the covering gets disturbed each time.
There is also the covering to think about. Any work at the frame means lifting tiles or slates around it, and every time an old covering is lifted and re-bedded you risk breakage and you disturb flashing that was weathering fine. Doing it once, properly, with a new unit, a new flashing kit matched to the covering, a fresh underfelt collar and a fresh insulation collar, resets the whole assembly to zero. That is why replacement is the honest recommendation on an aged unit, and it is the same logic set out for other worn components on rotten rooflights, replace not repair.
We never advise anyone onto their own roof to investigate a draught. Loft rooflights sit on a slope, often two storeys up, and the diagnosis is done from inside the loft and from a scaffold or tower at survey. If the unit is old enough to be draughty from a perished seal, it is old enough that replacement is the sensible answer, and we will price that as one written figure rather than a series of visits.
What a replacement puts right
Replacing a draughty loft rooflight is a like-for-like swap where the size and position stay the same, which keeps it to a one-day job in most cases. A modern unit brings a current gasket that will seal for years, a rigid frame that will not warp the way old timber did, factory-sealed double or triple glazing, and the chance to correct everything the old install skipped:
- A new flashing kit matched to your covering, so the weathering is right rather than tired.
- A fresh underfelt collar, so anything past the tiles is carried back out over the underlay.
- A new insulation collar and taped vapour seal, closing the cold bridge that made the reveals feel draughty.
- Splayed, re-plastered reveals, which throw more daylight and stay warmer.
The cost of a like-for-like replacement is set out on the pitched roof rooflight installation cost page, and if the room is dark as well as draughty, the daylight side is on loft rooflight daylight levels. Where the draught is really a phantom leak from the cold bridge, water through a loft rooflight covers how we tell the two apart.
Common questions about draughty loft rooflights
Can you just replace the seal on my loft rooflight?
We do not offer reseal or repair as a service. On a current unit a worn gasket can sometimes be swapped, but by the time an older rooflight is draughty, the seal is rarely the only thing gone: the sash has usually moved, the reveal is often uninsulated, and the frame may be loose. Fitting a new seal to that buys a season. We replace the unit so the fix lasts, and price it as one fixed figure.
Is the draught from the window or from the reveal?
Test it by weather. A draught that is worst on a windy day and comes from around the closed sash is a perished seal or a warped sash. A cold feeling that is worst in still cold weather, is even all the way round, and comes with staining on the reveals is an uninsulated cold bridge, not an air leak. The two get fixed differently, and both are usually put right in one replacement.
How much warmer is a new rooflight?
A modern double or triple glazed unit fitted with an insulation collar and a sealed vapour layer removes the cold bridge and the sash draught together. You feel it most as the reveals no longer running cold and the room holding heat overnight. We state the glazing U-value in writing on handover so the improvement is on paper, not just a promise.
Get a draughty loft rooflight replaced properly
Tell us roughly how old the unit is, what the roof is covered with and where the property sits. We survey from inside the loft and from a tower or scaffold, work out whether it is the seal, the sash, the reveal or the frame, and give you one written fixed price to replace it with everything itemised. Every installation carries a 10-year workmanship guarantee and the installers have 25 years fitting rooflights behind them.
Request a fixed quote for a loft rooflight replacement in Ipswich, Suffolk or north Essex, or look through our published prices first.
Thinking about this job? We survey across Ipswich, Suffolk and north Essex and give you a fixed price before any work starts, with a 10-year workmanship guarantee.