Yes, an old roof window can normally be swapped for a new one. The key is matching the new unit to the opening and fitting a flashing kit that suits your roof covering.
Many Kingsdown homes have roof windows added decades ago to loft rooms and top-floor spaces, and some are now tired, leaky or misting. Replacing one is usually a straightforward job on the roof side, but the detail matters, because most leaks at roof windows come from the surround and not the glass.
Looking at what is there
We start by checking the existing window, its size and the way it was fitted, along with the roof covering around it. We look at the timbers framing the opening, the flashing, and the lining inside. This tells us whether a like-for-like swap is possible or whether the opening needs adjusting. Age alone is not a reason to replace, but a leaking or misting unit that has been patched before usually is.
Matching the new window
Where we can, the new window is chosen to fit the existing opening, which saves cutting the rafters. VELUX and similar roof windows come in standard sizes, and the new one is matched to a flashing kit made for the roof covering. If the old size is no longer available, the opening can be altered, with timber trimmed and doubled up around it. A good fit matters as much as the product, so we measure the opening and the rafters rather than relying on the label.
Taking out and fitting
The old window is removed along with its flashing, and the tiles or slates around it are lifted. We check the felt and timbers, repair anything damaged, and fit the new frame and flashing kit so that water is taken around it. The covering is then put back neatly round the new window, with seals checked before we finish.
- Old window and flashing taken out carefully
- Felt and timbers checked and repaired
- New flashing kit matched to the roof covering
- Covering relaid tight around the frame
Inside the room
Inside, we check the lining, insulation and vapour control around the opening. A poorly insulated surround leads to condensation and cold spots even with a new window. Plaster and decoration are discussed beforehand so you know where our work stops. Some changes to the opening may need planning or Building Regulations checks, and we advise before work starts. If the lining has been damp for a while, the timber and plaster around the opening may need repair as well.
Access on tight terraces
Roof windows on tall terraces can be hard to reach. We plan access with a scaffold or tower where needed, so the work can be done safely and the roof is protected. It is worth replacing a window that leaks or mists before damp gets into the timbers around it. Once the new window is in, we show you how to open and clean it and how to use any blinds fitted.
Frequently Asked Questions
Does the old flashing get reused?
Normally no. A new window comes with a flashing kit matched to the roof covering, and fitting it properly is what stops leaks. Reusing old flashing risks a weak point at the most important junction. If in doubt, ask us and we will explain what we find.
Will the new window match the old size?
Often, yes. If the old size is not available or you want a different one, the opening can be altered with the rafters trimmed and doubled up. We explain the options on site. If in doubt, ask us and we will explain what we find.
Is it worth replacing just the glass?
If the frame, flashing and lining are sound and only the sealed unit has misted, new glazing may be enough. If the frame or surround is tired, replacing the whole window is usually better. If in doubt, ask us and we will explain what we find.
Talk to our team about VELUX and roof window installation in Kingsdown
Every roof is different — the fastest way to get an accurate answer is a quick chat with our team.