The short answer
Swapping a standard rooflight or roof window for a new one in the same opening is usually a one-day job on the roof and in the room. A sound frame that only needs a new sealed glass unit is quicker still, often a matter of hours. Anything that changes the opening, such as a bigger size, a new kerb or a rebuilt lining, takes longer, and the plaster needs further days to dry before it is painted.
Rooflight replacement time is set by the roof and the ceiling more than by the unit itself, which is why the survey comes before any date is promised.
A like-for-like swap
When the new unit is the same size as the old one and the roof around it is sound, the work follows a set order. The old frame and glazing come out, the opening is checked and cleaned up, the new unit is fixed, and the flashing or upstand is formed around it. Then the inside is made good. On a roof window in a pitched slate or tile roof, the roof side is typically done in a day. On a flat rooflight set on a kerb, the unit itself can go in quickly, but the roof covering around the kerb sets the pace.
The first part of the day goes on access and protection. Dust sheets go down, the furniture under the opening is moved or covered, and any scaffold or roof access is made safe. That time is not wasted. A room that is properly protected is a room that is clean when we leave.
Replacing only the glass
If the frame is in good order and only the sealed unit has failed, the new glass can be fitted into the existing frame without disturbing the roof covering or the lining. This is the shortest job of all. The old unit is lifted out, the rebate is cleaned, and a new sealed unit is set in on fresh packers and sealed. For a single rooflight it can be finished within a morning or an afternoon, depending on the size and weight of the glass and how it is reached.
Larger and heavier units take longer because they need more hands and often a lifting method. A big flat rooflight over a kitchen extension is not the same task as a small roof window on a landing. Our page on replacing just the glass in a rooflight explains when this route makes sense and when the frame should go too.
What stretches the day into a week
Several things turn a simple swap into a longer job, and most of them are found when the old unit comes out rather than before.
- a timber frame or kerb that has rotted, or a trimmer that has moved, which needs replacing before the new unit can sit square;
- a roof covering that has to be dressed back, such as slate or old tile that will not lift cleanly;
- a new size, which means cutting or trimming rafters, and that is a structural alteration;
- a lining that is out of square or has to be rebuilt to suit the new frame;
- poor access, such as a steep slope or a roof that can only be reached from inside.
A survey before the quote is where most of these are spotted. It is also why we write the roof and ceiling build into the finish schedule, so that the time on site is set by what is actually in the roof and not by a guess.
The finishing after the fitting
The rooflight is watertight at the end of the roof work, but the room is not finished. Where the old lining is reused, the plaster edges are made good, a fresh bead is fitted where the old one has gone, and the surface is prepared for paint. Where the lining is new, there is boarding or plastering to do first.
Plaster takes time to dry, and rushing it shows. A skim coat needs to dry before it takes mist coat and paint, and a lime plaster in an old house needs longer still. Plan for the decorating to follow a few days after the fitting rather than the same afternoon. If you want the opening left ready to paint so you can do the colour yourself, that is a line in the finish schedule. If you want it painted, that is a line too, and it adds to the time on site. The longer sequence is set out in our guide to how a rooflight is finished inside.
Old ceilings and thick walls
A lath and plaster ceiling in a Georgian terrace in St Leonards or Southernhay does not behave like plasterboard. Old plaster can crack if it is cut or vibrated carelessly, so the work around it is slower and more deliberate. The same goes for a cob cottage in the Culm valley, where the roof build is deep and uneven and the lime plaster should be matched with lime. Expect these jobs to take longer than a 1930s semi in Heavitree or a new build in Cranbrook, where the ceilings are plasterboard and the roof builds are regular.
The way to protect an old ceiling is covered in replacing a rooflight without damaging the ceiling. It is worth reading before you agree a timetable, because a rushed job is the one most likely to leave a cracked ceiling.
Building Control and the paperwork
Fitting a complete new rooflight or roof window, including its frame, is notifiable building work, as the new window is a controlled fitting and Part L applies. Building Control is told by us, so it does not add to your list. A glass unit swapped alone into the existing frame is not notifiable. The paperwork runs alongside the work and does not usually add days to the fitting itself, but it is part of the job being complete.
Planning the timetable
A few practical points keep the job to its shortest sensible length:
- Clear the room under the rooflight, or agree who will move what.
- Tell us about access, parking and any scaffold constraints at the survey.
- Choose the finish before the day: ready to paint or painted, straight or splayed lining.
- Allow for dry time between the plaster and the paint.
The written quote sets out what is being done, and the finish schedule sets out how the inside will be finished. Together they give you a timetable that matches your roof, not a general figure. To get one for your home, ask for a quote and we will look at the roof and ceiling at the survey.