How Much Does It Cost to Fit a Velux Window?

Checkatrade's window fitting guide, updated for October 2026, gives average costs of £1,250 for installing a new Velux-style roof window and £1,025 for replacing one. Those are national averages, not Crown figures, and a real quote can land well above or below them. Checkatrade's separate repair guide, from July 2026, puts a Velux repair at £165 to £1,050 and £1,000 to £2,500 to replace the whole window like for like.

The gap between those two replacement figures is a reminder that averages hide a lot. A small window on an easy slope is a different job from a big one above a stairwell. Treat the numbers as a yardstick for whether a quote is in a sensible region, not as a price to expect. Ask any roofer whether the figure includes VAT, scaffolding and the inside finishing, because guides and quotes do not always count the same things.

If a quote is much lower than the guides, ask what is missing. If it is much higher, ask what makes your roof harder. Our roof windows and skylights page explains what we fit and how we price it after a survey.

Swapping a window for another of the same size uses the opening that is already there. The old unit and its flashing come out, the new window and flashing go in, and the inside lining is usually left alone. It is the simpler job, and the guide figures reflect that.

A new opening is a bigger job. Rafters have to be cut, and a trimmer fixed above and below the gap to carry the load. The covering is lifted and cut round the frame, and the new window is weathered in with flashings that suit your tiles or slates. Inside, a lining is built, plastered and decorated, and the whole thing must be made safe and weathertight in a day or two. That is why a new opening costs more than a replacement.

It may also need paperwork. Crawley Building Control names new window openings in roofs or walls as work that needs approval, and the Planning Portal counts roof windows within the building envelope. Check with your building control body before work starts. Our answers on replacing a Velux with a bigger window and fitting a Velux in a slate roof show how the cuts change.

Window size is the obvious factor, and our answer on Velux window sizes explains the range. The roof covering matters just as much. Flashing kits differ for plain tiles, interlocking tiles and slate, and a slate roof takes more care to cut and re-lay around the frame.

Access is the next factor. A window over a first-floor landing can be reached from a tower or ladder, while one on the rear of a two-storey house may need scaffold, and scaffold can add a large share of the total. Ask whether the price includes it. The number of windows fitted in one visit helps too, because the access, the mess and the tidying are done once.

Last, the finishing inside. Plaster, a deeper or angled lining, painting and a blind are not always counted in a guide figure. If the loft is already boarded and lined, less is needed. If the room is a new conversion, there is more. Our survey covers the roof, the rafters and the room below, with photos sent to you afterwards.

Planning is usually simple for a roof window. Under Class C of Schedule 2, Part 1 of the General Permitted Development Order, the alteration must stand no more than 0.15 metres proud of the original roof plane, stay below the highest point of the roof, and meet the remaining limits. Any window in a side-facing roof slope has to be obscure-glazed and, unless the openable parts are more than 1.7 metres above the floor, non-opening.

Those rights do not apply to flats, while a listed house also needs listed building consent where its character is touched. Conservation areas and National Landscapes are article 2(3) land, which affects dormers but leaves Class C roof windows within its limits. A local Article 4 direction can still remove rights, so check with the council's planning team.

On top of planning, a new window must meet energy rules. Approved Document L 2021 sets 1.4 for a new window and 2.2 for a rooflight in an existing home. Once we have surveyed, the single written total names the glazing, so you can check it against the data sheet and the guides above.