An old VELUX window that sticks, drips, mists between the panes or lets the draught in has usually reached the point where replacing it makes more sense than carrying on. This page walks through how to replace an old VELUX window: how to tell when it is time, what the job involves from the scaffold to the plasterwork, and what the rules say. It belongs to our wider guidance on VELUX windows in Brighton & Hove.
Signs the window has reached the end
Old roof windows and skylights rarely fail all at once. They give notice. Moisture appears between the two panes of glass and will not wipe away, because the sealed unit has failed and the gas or dry air inside has been replaced by damp air. The sash drops and rubs on the frame, so it will not close tight. The handle or the control bar feels loose or gritty. A brown stain spreads on the lining below the frame after rain. You can feel cold air at the edges on a windy night.
Any one of those is worth taking seriously. Several together point to a window that has done its time. A failed sealed unit cannot be repaired, so the honest answer is that the glass, or the whole window, needs to be replaced. We cover the glass question in a separate page, can you replace just the glass in a VELUX, and the full unit is the focus here.
Glass only or the whole window
When the frame is sound and only the sealed glass has failed, replacing the glass alone can be an option. When the frame is damaged, the flashing has perished or the window is of an old generation that no longer meets modern standards, the whole unit should come out. The choice depends on what we find at the survey, not on a rule of thumb.
Taking out a whole old window and fitting its equal is building work. Part L of the Building Regulations asks a new roof window in an existing dwelling to achieve Window Energy Rating band B or 1.4 W/m²K. A sound existing frame fitted with new glass alone is not a controlled fitting under Approved Document L. The Building Regulations explainer discusses both routes.
| What we find | Likely route | Why |
|---|---|---|
| Sound frame, failed glass only | Glass can be considered | The frame and flashing are still doing their job |
| Rotten or swollen frame | Whole window | New glass cannot fix a frame that no longer seals |
| Perished flashing or slipped covering | Whole window with new kit | The weathering around the frame has to be reset |
| Early generation unit | Whole window | The old specification will not reach current standards |
Getting the right replacement
A like-for-like swap starts with the label. The size code, such as MK04, tells you the width and height of the frame, with the letter as the width and the digits as the height. The type code, such as GGL or GGU, describes the build. We explain each in our guide to VELUX size codes and in our guide to VELUX window types.
The same size does not always mean the same fit. Over the years the frame depth, the flashing and the glazing have changed. The new window usually drops into the old opening, but the flashing kit has to suit the new frame and the roof covering around it, whether that is plain tile, slate or something else. We always specify the kit by name in the written quote.
What happens on the day
The job follows a set order. The steps below are the ones we take on a standard like-for-like replacement.
- Set up the access. The scaffold, tower or platform goes up as set out in the access plan, with the licences already in place.
- Protect the room. Dust sheets cover the floor and furniture, and we clear the area below the window.
- Remove the old unit. The sash and the frame come out, and the old flashing and the roofing around it are lifted back.
- Check the opening. We look at the rafters, the trimmers and the battens, and replace any timber that has rotted.
- Fit the new window and flashing. The frame is fixed, the flashing is set in order from the bottom up, and the covering is re-laid over it.
- Finish inside. The lining is sealed, the sash is adjusted, and we show you how the window opens and closes.
A straightforward replacement in good access is often a one day job. Whether yours is depends on the roof and the weather, and we cover that in our page on whether a VELUX can be fitted in a day.
Reaching the roof in Brighton and Hove
The window itself is the easy part of the job. The harder part, in this city, is often the route to the roof. A tall terrace in Hove may need a tower from the street. A mansard in a conservation area may call for a scaffold across the pavement. A converted flat may have the roof above a communal stair. Each quote we write carries the access plan, a written page showing how we get up there, who makes the council scaffold licence and bay suspension applications (we do), what the neighbours are told and the Building Control route. Which highway authority grants the licences, and what is involved, is on the licensing page.
Narrow streets and permit-only parking can make the difference between a smooth day and a stalled one. That is why the access plan is written before the work starts, not worked out on the morning.
Inside the room: lining, blinds and disruption
The roof is only half of it. The inside of a loft room takes the mess, so we plan for it. Furniture is moved clear or covered, the floor under the window is sheeted, and we take down the blind and any curtain pole fixed to the frame. If you have a blind that fits the old window, tell us at the survey. Blinds are made to suit the frame, and a blind from an old unit may not fit a new window even of the same size code, so we check before we assume.
The plasterboard or timber lining around the frame is the other thing to think about. Where the new frame is the same size as the old, the lining stays. Where the new frame sits slightly differently, a strip of lining may need to be trimmed, filled and painted. We tell you in advance, so the job does not end with a gap you did not expect. If the loft room is already decorated, you may want to touch up the paint once the sealant has cured.
Plan to be out of the room while the roof is open, and keep children and pets clear of it. The opening is covered as the work proceeds, so the house stays weathertight at the end of each working day.
Questions to ask before you book
Whoever you ask to replace your window, a handful of questions will tell you whether the job has been thought through. Ask who is applying for the scaffold licence and the parking bay suspension, because the council needs the application before the scaffold can go up on the pavement. Ask how the Building Control notification is handled. Ask what happens if the rafters or battens behind the frame turn out to be rotten, because that can turn up on an older roof. Ask what is written down: the unit, the flashing kit, the access route and the price.
Our answers sit in the written quote and the access plan, so you do not have to rely on a conversation. If a survey turns up something extra, such as a trimmer that needs strengthening, we tell you before any work starts and the fixed figure is revised in writing, not after the fact.
Permissions, from planning to the freeholder
For a house, the replacement of an existing roof window like for like is normally straightforward. Houses may add rooflights under permitted development as long as no unit sticks out above the roof slope by more than 150 mm, and each sits below the roof's highest point. Living in a conservation area leaves those rights in place, though an Article 4 direction takes them away, and the city council applies such directions in a good number of its conservation areas. Listed buildings need listed building consent too. If you are unsure, check with the council after reading the Brighton and Hove planning guide.
Flats are different. Permitted development does not reach them, so a new rooflight in a flat needs planning permission. Where a house has been converted, ownership of the roof generally lies with the freeholder, and the leaseholder usually has to obtain a licence for alterations. Check your lease before anything is ordered, because the answer can change what is possible on the roof, how long the paperwork takes and who has to be told first; the consent side is covered under flat and leasehold rooflights. Inside the South Downs National Park, planning decisions come from the park authority, while Building Control stays with the district council.
How long an old window should last
There is no fixed life for a roof window. How long one lasts depends on the quality of the build, the exposure of the roof, the room below and the care it has had. Salt-laden air near the coast and strong south-westerly wind tend to be harder on frames and seals than a sheltered inland roof. Our page on how long VELUX windows last goes into the factors in detail. For this page the practical point is simple: if the window is failing, fix the cause by replacing it, because a failed unit does not recover.
Cost, without the guess
The price of replacing an old VELUX window depends on the size, the type, the glazing, the flashing kit, the roof covering, the amount of timber repair behind the frame, and above all the access. A ground-floor extension roof reached by ladder is a different job from a fourth-storey roof that needs a tower and a licence. We do not give a price in a general article, because the figure would mislead. The free survey produces a fixed written quote, and the access plan sets the price against the route to the roof. If you want to understand how pricing works first, read how much it costs to fit a VELUX window.
Is it time to change brand?
Some owners ask whether they must replace an old VELUX with another VELUX. You do not. A different make of roof window can fit the same opening, provided it is the right size and the flashing suits. Whether it is the better choice depends on the opening, the budget and the look you want inside. We look at the alternatives in our page on alternatives to VELUX. Staying with the same make is a perfectly sound decision, because the opening is already sized for it.
What stays with you after the job
When the work is done, the opening is weathered, the lining is finished and you can use the window. If the swap is notifiable, the notice to Building Control comes from us, and you are handed the paperwork. A 10-year workmanship guarantee stands behind the fitting, and the guarantee page sets out the terms.
If your old window is showing its age, go back to the VELUX windows hub or book a free survey. We will inspect the window, set out the access plan and give you a fixed written quote.
