Can I fit a roof window myself?

A roof window is not screwed on top of the roof like a rooflight kit on a shed. It sits in an opening cut through the tiles or slates, the battens, the felt below them and, nearly always, a rafter, and then it has to be sealed back into the roof so water runs over it and around it, never under it.

In order, the work is: strip the tiles or slates around the chosen spot, cut the opening, trim and double up the rafters when the frame is too broad to fit between neighbouring timbers, fix a support frame, set the window, fit the flashing, and lay the covering back. Flashing is the formed metal that overlaps the window frame and the roof covering to shed water. Inside, the opening then needs lining, insulating and finishing. Each stage depends on the one before it, and a mistake at the first stage shows up as a leak at the last.

The tricky parts are the ones you cannot easily see from inside the loft: whether the rafters are sound where you cut, how the underlay is dressed into the frame, and whether the flashing laps are the right way round for the covering you have. Slate, plain tile and pantile each need a different flashing, and a kit bought for the wrong covering will not seal properly.

This is the part DIY guides tend to skip. The Planning Portal lists structural alterations among the things that need a building control application, and cutting through rafters to make a new roof opening is a structural alteration. Our page on roof window Building Regulations goes through the detail.

The energy rules matter too. Under Approved Document L, a roof window put into an existing home, new or as a replacement, has to reach 1.4 W/m²K or else earn a Window Energy Rating of Band B. If the loft becomes a bedroom or other habitable room, Approved Document B on escape comes into it. On a two-storey house a loft room needs either a protected stairway or an escape window with an openable area of at least 0.33 m², no less than 450 mm in height and width, with the bottom of the opening at most 1100 mm off the floor. Not every roof window meets that, so the choice of model is part of the compliance question.

For sign-off you can choose between the council's own building control officers and a registered building control approver. Swindon Borough Council runs its own service. Ask before you start, not after, because putting right unapproved work is harder than getting approval first.

Many houses can take roof windows as permitted development under Class C, provided the window does not stand proud of the roof plane by more than 0.15 metres and sits below the ridge line of the original roof. On a slope that faces the side of the house, every window has to be obscure-glazed. The 1.7 metre height only changes the rule about opening, not the rule about obscure glass.

Listed buildings need listed building consent, and an Article 4 direction can remove permitted development rights in some conservation areas. If you are unsure, ask Swindon Borough Council's planning team before ordering anything. Our guide to roof window planning permission covers the checks.

The practical risks are bigger than most people expect. You will be on a pitched roof, handling a glazed unit that can be heavy and awkward in any breeze, with a hole open to the weather. Scaffolding is the safer way to work, and MyBuilder's roof window guide puts it at around £500 for a typical job, which is a sizeable share of the money DIY is meant to save.

Weather is the second problem. Once the covering is off, you are committed. A shower arriving halfway through leaves wet insulation and a soaked ceiling. Professional crews plan the opening so it is weathertight again by the end of each working period, and they carry sheeting for the moments when it is not.

Then there is the loft below. Insulation, wiring, water pipes and stored belongings all sit within a metre or so of the opening, and falling tiles, dust and cut timber have to go somewhere. Good preparation inside the loft takes as long as the roof work.

Manufacturers write their guarantee terms around correct installation. Read yours before deciding. If a leak appears and the window or flashing was fitted by the owner, the manufacturer can reasonably point to the installation as the cause, and your home insurer may take a similar view. Neither is a certainty, but both are risks.

When we fit a roof window, the workmanship is covered by a 10-year guarantee in writing, so a leak around the flashing is our job to put right. That is a promise about our work, not insurance, and it only covers what we fitted. A DIY fit carries no such backing unless you can prove the instructions were followed to the letter, and that is difficult to show after the covering has been relaid.

MyBuilder's roof window guide, updated in August 2026, puts installation at £350 to £600 for standard jobs, labour and fitting included, with a basic centre-pivot unit at about £305. Electric versions run higher. Treat these as UK averages that say little about the price for your roof.

Set against the scaffold, the building control fee and the cost of a mistake, the saving from DIY is smaller than it looks. Our roof window or skylight page explains the products, and where to put a roof window helps you choose a position. Whether the roof can take a window at all is covered on can a roof window fit any roof.

If you would rather have it fitted, send us photographs and we will survey the roof, photograph it, and put the price in writing. Our skylights and roof windows page lists everything we do with them.