The short answer
The cost of replacing a rooflight comes from four places: the new unit, the way we reach the roof, the covering around the opening, and how much of the ceiling lining inside has to be remade. A like-for-like swap into an opening that is sound sits at the simple end. A larger or different unit that needs timbers trimmed sits at the other. We give no figure until we have seen the roof.
- Free survey, fixed written quote
- 10-year workmanship guarantee
The unit going in
Start with what you have now. A pitched roof window, a flat rooflight on a kerb and a roof lantern are replaced in different ways, and each comes in a range of sizes, glass specifications and opening types. A fixed unit costs us less effort than one with an electric actuator and a power supply to connect, and a long run of glazing bars costs more to make than a plain pane.
The energy limit also shapes the choice. Under Part L, a new or replacement roof window takes the window limit of 1.4 W/m²K, or Window Energy Rating band B at minimum, and a rooflight or lantern takes 2.2 W/m²K. We specify to those limits, so an old single-glazed or tired double-glazed unit will come back as a better-insulated one.
If the glass has misted but the frame is sound, a glass-only exchange may be possible, which is covered under misted rooflights.
| What is there now | Usual route | What drives the work |
|---|---|---|
| Roof window in a pitched roof, size code known | New window and flashings into the same opening | Matching the flashing to the tiles or slates |
| Flat rooflight on a timber kerb | New unit onto the existing kerb if it is sound | Condition and height of the kerb |
| Misted sealed unit in a good frame | Glass-only exchange | Whether the frame and its seals are in good order |
| Lantern with a failed frame | Whole lantern, with the kerb checked | The roof edge and covering around it |
Reaching the roof and what covers it
A ground-floor flat roof over a utility room can be reached by a ladder and a short carry. A window high on the roof of a three-storey house needs scaffolding or a tower, and that time and hire goes on the quote as access. Tight side passages and a small garden can slow the carrying of a large pane of glass, so we look at the route as well as the roof.
The covering around the unit matters as much. On a tiled or slated pitch, the flashing has to lap with the courses beside the opening, so those tiles or slates are lifted and relaid with the new flashing. Pieces that are cracked or slipped near the frame are replaced as the work goes. On a flat roof the membrane is dressed up the kerb, and a worn membrane near the edge may have to be renewed around the unit. We check all of this from the roof at survey, and it is itemised on the quote.
Our guide to flashings for Kent roofs explains what goes under and around a window on different coverings.
Remaking the lining indoors
Take a landing lit by one roof window above the stairwell. If the new unit has the same size code as the old, the lining around it often needs only filling and repainting. If we change the size, the plaster splay is cut back or built out, new reveals are formed and the decorating covers a larger area.
Access can matter inside as well. Working over a stair opening may call for a platform, and in a loft study or a bedroom in the roof, furniture and floors need protecting. Where a blind, a pole or an electric opener is fitted, the lining and wiring are part of that item.
A stairwell landing can need a working platform before the first tile moves.
Lines on a replacement quote
Our written quote breaks the job into lines, so you can see where each part of the cost sits and compare it with any other. The survey is free and the quote is fixed. We handle the Building Control notification where the work is notifiable, and the workmanship carries our 10-year guarantee in writing.
For wider context, our costs page sets out what moves prices across the whole range, and the cost answers for VELUX windows and roof lanterns go further on each product.
Lines a replacement quote carries
- The new unitSize, glass specification and opening type
- AccessLadder, tower or scaffold, and the carry from the van
- Removal and disposalTaking the old unit out and away
- Flashing or kerb workNew flashings, or the kerb and membrane on a flat roof
- Lining and decorationReveals, plaster and paint inside
