Like for like swap
Can an old Velux window be replaced like for like?
An old roof window can be swapped for a new one in the same opening, without cutting the roof again. Below: how a swap works, the rules and published prices.
The short answer
Yes, where a window of the right size exists, an old Velux can come out and a new one go into the same opening, with a fresh flashing kit over the top. The rafters and the room's lining stay where they are. The new window must still reach the present energy standard for a roof window, and the survey measures the opening first, because a size that fits the old frame has to exist in the new range.
4 min read · Part of Roof windows & skylights
What like for like means on a roof
On a roof, like for like means the same opening, not the same logo. The new frame has to sit between the rafters that already carry the old one, so the outside dimensions of the new window are matched to the gap. A window one size larger would mean cutting a rafter, and then the job is a new opening, which carries its own checks.
The survey measures four things before any window is ordered:
- the width and height of the old frame, taken from the loft side as well as outside
- the pitch of the slope, since each model has a pitch range on its data sheet
- the covering round the frame, which decides the flashing kit
- the state of the battens and underlay at the edges of the opening, because a new frame set into soft timber will not hold
If the old make has been replaced in the range, the survey checks the current range for the same size, and a different make can be chosen if you prefer. Where no size fits, you hear that before anything is ordered.
How a swap is done
A swap involves less cutting than a new opening, and it follows a set order:
- The tiles or slates round the frame are lifted, and the old flashing comes off with them.
- The sash is taken out, then the frame, and the opening is checked for damp or damage.
- New battens go in where the old ones have softened, and the underlay is renewed round the opening.
- The new frame is set in, levelled with a spirit level, squared to the opening and fixed to the rafters.
- The flashing kit is fitted for your covering, and the tiles or slates are refixed over it.
- The sash goes on, and we check that it opens, closes and seals.
Inside, the lining panels can stay in place. If the old frame has rotted or held damp, the lining panels and the insulation behind them are checked before the new frame is closed in.
Where a scaffold is needed, and on a tall slope it may be, it sits inside the written price, and we arrange the licence with our scaffolder if it stands on the pavement.
Rules that apply to a swap
Any new roof window must reach the energy standard in force. Until 24 March 2027, Approved Document L 2021 Table 4.2 asks for 1.4 W/m²K or Window Energy Rating Band B from a roof window, and holds a rooflight to 2.2 W/m²K, so the two are not interchangeable.
The council side depends on the address. In the Dover district, the council's building control page puts installing roof lights on its list of work needing approval, so a call to that council comes before any swap there. In other districts the local building control team is asked first, and the answer is noted in your written price.
On planning, a house can use permitted development under Class C, but a flat cannot, a listed home needs listed building consent, and an Article 4 direction can remove rights. Our conservation area page covers the question for those streets.
Where the window is also a loft room's way out in a fire, the new one has to keep an openable area of at least 0.33 m² and stay within 1100 mm of the floor, as Approved Document B sets out.
What a swap costs, from published guides
Two sources give a price for a Velux window. Checkatrade, in its repair rates, lists rooflight replacement, for example Velux, from £1,000, and that starting figure is the one it publishes.
MyJobQuote's figures sit in the table, and the guide states no VAT basis for them. Neither guide has seen your roof, and each may group its jobs differently from the other, so treat both as a sense of the scale and no more.
| Figure | What it covers |
|---|---|
| £1,100 | Average for a standard mid-range window |
| About £100 less | A straightforward swap, opening in place |
What we give you is one written total price, set after the survey, with any scaffold inside it. The page on installation cost lists what moves it, and the roof windows and skylights page shows the whole service. A swap that exposes rot or damp round the opening can move the price, so the survey looks at the timbers before the figure is written, and you see the result in writing before work is booked.
More questions
Can the new window be bigger than the old one?
Only by treating the job as a new opening. A bigger window means cutting into the roof framing, so the survey looks at the rafters, the pitch and the covering again, and the planning and building control checks for a new window apply. A like-for-like swap keeps to the size the old frame already has.
Is the flashing replaced along with the window?
Yes, a new frame gets a new flashing kit. Each kit is cut to suit one covering, and the old pieces are shaped to the old frame, so they come off with it. The tiles or slates beside the frame are lifted and refixed over the new kit before the job is closed.
Tell us what's wrong with the roof.
You'll get one written total price.