A rooflight job is priced from the roof, the opening and the finish inside the room. Two houses on the same street can need very different amounts of work for what looks like the same window. The roof, how big the opening is and the glazing specification move the price, product by product, and each product has a longer cost guide.
The figure for your house comes from a free survey and arrives as a fixed written quote.
By product
What sets the cost of each product
Each product has one or two things that matter more than the rest, and each has a cost guide: roof lanterns, flat roof skylights, roof windows, VELUX windows, electric opening units, walk-on glass and sun tunnels.
| Product | What drives the cost | What the survey checks |
|---|---|---|
| Roof lantern | Size of the opening, glass specification, the upstand it sits on | Roof build-up, structure under the opening, access for lifting |
| Flat roof rooflight | Set by the roof, the kerb and the glass; the flat roof skylight cost guide has the detail | Existing covering, falls, whether a kerb is already there |
| Roof window | Frame size, flashing set, internal lining | Rafter spacing, pitch, tile or slate type |
| Electric opening unit | Motor and controls, power supply route | Where a cable can reach, rain sensor position |
| Walk-on glass | Glass build-up, load rating, supporting frame | The structure that carries the load |
| Sun tunnel | Tube length, rigid or flexible run, diffuser | Route through the roof space, ceiling depth |
On the roof
The roof you already have
Peg tile, slate, concrete tile, felt, EPDM, GRP and lead each need a different method to open and make good. A flat roof that already carries an upstand costs less to prepare than one that needs a new kerb built. A pitched roof whose rafters sit closer together than the window is wide may need trimming in, and that adds timber and labour.
Height matters too. A single-storey extension is reached from a ladder, while a three-storey house may need scaffold or a tower, and that changes the number of days on site.
What the roof adds
- Covering typeTile, slate and flat membranes are cut and sealed in different ways.
- StructureTrimmed rafters, new joist work or a kerb build.
- AccessLadder, tower or scaffold, and room to lift glass.
- InsulationWarm or cold roof build-up around the new opening.
The unit
Glass, frame and how it opens
Specification moves the price as much as size. Double and triple glazing, self-cleaning or solar-control coatings, laminated inner panes and walk-on build-ups all cost differently. A fixed unit is simpler than one that opens by hand, and one that opens on a motor with a rain sensor is simpler to fit than one that also needs a cable run across the ceiling.
For a replacement, the question is whether the new unit matches the old opening or needs it enlarged. A like-for-like swap keeps the structure undisturbed. Changing the size does not.
Inside the room
The finish indoors
Light shafts, plasterboard lining, decoration and making good around a ceiling opening are part of the job. A roof window on a loft slope is usually a short return in the room. A rooflight over a ground-floor extension may sit directly on the ceiling. A sun tunnel through a first-floor bathroom ceiling and a tiled roof means working across two floors. Tell us if you want the decoration finished by us or left for your own decorator, and the quote will say which.
What a quote should list
The product and its specification, the size of the opening, the roof work, the lining inside, the Building Control notification where the work is notifiable, the guarantee, and anything excluded.
Rules and paperwork
Paperwork that sits in the job
Planning checks, Building Regulations compliance and notification are part of the work, and so is energy performance. A new or replacement roof window has to meet 1.4 W/m²K (or Window Energy Rating band B), and a rooflight or lantern 2.2 W/m²K. The two longer guides on planning permission and Building Regulations set out when each applies. If your question is simply what a replacement costs, this answer goes through it.
When you are ready, the form is the way in.
