Velux reglazing
Can a misted or cracked Velux window be reglazed?
Mist between the panes may need only new glass, while a rotten frame or a leak points to a new window. Below: how to tell the two apart.
The short answer
Yes, a misted or cracked Velux window can be reglazed where the frame, the seals and the roof around it are still sound. The glass unit is renewed and the window stays in its opening. Where the timber is soft, the sash no longer closes squarely or the flashing lets rain in, new glass would be spent on a failing window, and replacing it is the better route.
5 min read · Part of Roof windows & skylights
What mist and cracks tell you
A roof window pane is normally a sealed unit: two sheets of glass with a gap between them. When the edge seal fails, damp air creeps into the gap and leaves a film or beads that no amount of wiping will reach. That is a glazing fault and not a roof fault, and the window may still keep the weather out perfectly well.
Droplets on the room side are a different matter. They come from damp air in the room, and new glass would meet the same air. Our page on condensation on Velux windows explains how to separate the two.
A crack may come from a knock, a stone or stress in the glass. It lets the sealed unit breathe, so a cracked pane can mist soon afterwards. Do not lean out to inspect a cracked pane or reach up to it: broken glass overhead is a hazard, and the survey is the safer way to look at it.
Photographs taken from inside the room, in daylight, help us judge it before we visit.
New glass or a new window
The choice turns on what else has aged, and not on the glass alone. Reglazing makes sense only when everything holding the glass still has years in it. The table sets out the usual readings from a survey. Mention it when you call if the sash sticks, has been painted shut or sags in its frame, since that tells us how the timber has moved over the years.
| What the survey finds | Likely route |
|---|---|
| Mist only, frame and seals sound | Renew the glass unit |
| Mist plus a soft or stained frame | Replace the window |
| Crack, with the sash closing squarely | Renew the glass unit |
| Leaks round the frame after rain | Check the flashing, then decide |
The make and age of the window matter as well, because parts are not made for every model for ever. If the right glass unit cannot be supplied, replacement becomes the practical route, and our page on replacing an old Velux like for like covers it. A survey settles all of this on the day. Where glass is the only fault, you are spared a new frame, new flashing and new lining, and the disruption inside the room is far smaller than a full replacement brings.
Part L and the price to compare
Until 24 March 2027, AD L 2021 Table 4.2 sets 1.4 W/m²K or Window Energy Rating Band B as the limit for roof windows put in an existing home, with 2.2 W/m²K held back for rooflights alone. Whether renewing only the glass in an old frame brings those figures into play is a question for building control, so we put it to the council team before starting any job where it might. A window in a listed home or a conservation area has further rules of its own, which we check at the same time.
On cost, MyJobQuote reports an average of £1,100 for a Velux window of standard size and mid-range specification, and says a straightforward swap runs around £100 less because the opening already exists. That is the price of a whole window, not of new glass, which makes it the number to hold a reglazing price against.
What new glass costs depends on the size, the make and the type of glazing, and it is fixed once the unit has been identified. Reglazing is then quoted as one total price, with the scaffold, if the roof needs one, inside it.
Checks made at the survey
Most of the useful evidence sits on the roof and in the frame, not at the pane. On a visit to a misted or cracked window we check:
- the make, size and age, read from the label on the sash
- whether the sealed unit is misted, cracked or both
- the timber of the frame and sash for softness, stains or splits
- the flashing and the roof covering round the opening
- the lining and plasterwork inside, for marks left by earlier leaks
You then hear what the window needs and whether new glass is a sound repair or a window that is close to worn out. Our page on how long Velux windows last puts the age in context, and the roof windows and skylights service page sets out the wider range of work we do with them.
Both are worth a read before you decide, and the survey will tell you which route the numbers favour. Bring the window label, if you can find it, and a note of any past repairs, because both save time on site and make the answer firmer.
More questions
Can I reglaze a Velux window myself?
The glass unit is heavy, and the work is done on a sloping roof with the weather turning. It needs a roofer with scaffold or a roof ladder and the right lifting gear. Taking a sash apart without a plan can leave the opening unprotected in rain, so we would rather look at it than have you attempt it from a ladder.
Will new glass stop the window leaking?
No, since a leak and a failed glazing unit are separate faults. The glass is sealed from the inside, while a leak comes from the flashing, the frame or the roof covering around it. If water comes in after rain, the survey checks those parts, and renewing the glass alone would not cure it.
Tell us what's wrong with the roof.
You'll get one written total price.