Replacing an old roof window
In short
A tired roof window can usually be swapped straight into the existing opening with a new flashing kit and no structural work at all, because the major manufacturers have kept frame sizes stable for decades. It is a considerably smaller job than most people expect.
Also called: Replace Velux · Old skylight replacement · Roof window swap · New rooflight in existing opening
Signs you need this
- Draughts around a roof window even when it is shut
- Misting between the panes of the glazing unit
- Condensation running off the frame onto the sill
- Rot or softness in the timber frame or sill
- Handles, catches or opening gear that no longer work
- A unit that will not seal properly when closed
Roof windows age in predictable ways. The seals go hard and stop sealing, so draughts and condensation get worse. The timber frame on older units softens where water has been sitting on the sill. The glazing unit fails and mists between the panes. The operating gear stiffens or breaks. None of those is a reason to touch the roof structure.
The genuinely good news is size compatibility. The major manufacturers have kept their frame dimensions consistent for a very long time, so a window fitted in 1995 can very often be replaced with a current model that drops into the same opening. Whether that is true of yours is a five-minute check of the data plate on the sash, which carries the size code.
A straight swap is a contained job: the old unit out, the opening checked and any rotten timber made good, the new unit in, and a new flashing kit dressed into the covering. No rafters cut, no structural work, no Building Control. Where the covering has to be lifted around the opening it goes back afterwards, so the disruption outside is limited to that immediate area.
The flashing kit is not optional and it is not reusable. Old kits corrode and distort, and they were made for the old frame profile. A replacement window fitted using the previous kit is the second commonest cause of a leaking roof window, after using the wrong kit type in the first place. The kit has to match both the new unit and the covering it sits in.
Modern units are a substantial improvement, which is worth knowing when weighing repair against replacement. Current glazing is far better thermally than anything from the 1990s, the seals and the ventilation flaps work properly, and there are options — solar-powered opening, blinds, laminated or toughened glazing for a bathroom or over a stairwell — that older units did not have.
The one case that turns a swap into a bigger job is a rotten opening. Where the window has been leaking for years, the trimmer timbers around it can have gone, and that has to be repaired before a new unit goes in. It is not common, and it is exactly the sort of thing that gets found when the old unit comes out rather than beforehand — which is why an honest quote allows for looking.
What the job covers
- Size code checked to confirm a straight swap is possible
- Old unit removed and the opening inspected
- Any rotten trimmer or sill timber repaired
- New unit fitted into the existing opening
- New manufacturer flashing kit correct for the covering
- Covering lifted and re-laid neatly around the opening
What it costs
We don't publish a price for this yet, because a number pulled out of the air is worse than no number at all — your roofer has to honour it. On roofing it would also be close to meaningless: access is often the biggest single factor, and it varies enormously house to house. You'll get a firm price for your actual job when they ring you back, before any work starts. The quote itself is free and there's no obligation either way.
Common questions
Will a new window fit my old opening?
Very often, yes. The major manufacturers have kept frame sizes stable for decades, so a unit from the 1990s can usually be replaced by a current model in the same hole. The size code is on a plate on the sash — a two-minute check that tells you whether this is a simple swap or a bigger job.
Can the old flashing kit be reused?
No. Old kits corrode, distort and were made for the previous frame profile. Reusing one is a common cause of a replacement window leaking, and it saves a small fraction of the job cost while risking the whole thing. A new kit matched to both the unit and the covering goes on every time.
Is it worth repairing instead?
Sometimes — handles, catches and blinds are all replaceable, and a failed seal can occasionally be dealt with. Where the glazing unit has misted or the frame has softened, replacement is usually better value, and a modern unit is substantially better thermally than anything from twenty years ago.
Will it need Building Control?
Not for a like-for-like replacement into an existing opening — no structure is being altered. If the opening is being enlarged, or extra units added, that changes the answer because rafters are being cut. Worth confirming the scope before assuming either way.
Need this doing in Macclesfield?
Tell us the job and it goes straight to our local roofer — one call back, usually the same day. Free quote, no obligation.