The short answer
Swapping an existing roof window for a new one of the same size can often be done in a day. Cutting a new opening in a roof usually takes a few days on site, once the lining and plaster are counted, and a roof lantern or a large flat rooflight takes longer still. The roof is made weathertight on the first day or two. The rest of the time goes on the inside.
Skylight installation time is the same story across roof types: the weathertight stage is short, and the finishing is where jobs differ. That split is why a single number never tells you much. A quote that says "one day" may be describing the glass and flashing only, while the ceiling is left raw. A skylight fitting time is worth asking about in two parts: how long until the roof is sealed, and how long until the room is finished.
Fitting times by type of rooflight
These are typical spans for a straightforward house. Access, roof condition and the room all move them, so treat them as a guide to the shape of the job, not a promise.
| Job | Roof made weathertight | Room finished |
|---|---|---|
| Replacing a roof window like for like | Usually within the day | Often the same day, if the lining is sound |
| New roof window in a pitched roof | One to two days | Two to four days in all, with plastering |
| Flat rooflight on an existing upstand | About a day | Usually a day or so more |
| New flat rooflight with a new kerb | Two days or more | Several days in all |
| Sun tunnel | Part of a day to a day | Often done with the fitting |
| Roof lantern | Several days, with the kerb built first | A week or more in all |
What happens on the first day
On a pitched roof, the day starts with protecting the room and setting up access. Tiles or slates are lifted around the opening, the rafters are trimmed and a framed opening is formed, and the new unit is fixed and flashed. The aim is that by evening the roof is closed and the weather can't get in, whatever the forecast does overnight.
A new opening takes longer than a replacement because of the structure. Cutting a rafter means fitting trimmers either side so the load is carried round the opening, and that has to be right before anything else goes in. It is also building work, so the Building Control notification is dealt with before the roof is opened. We handle that for you, and it doesn't hold up the programme once the paperwork is in.
A like-for-like replacement is quicker because the opening already exists. The old unit comes out, the flashing is renewed to suit the new frame, and the new window is set in the same place. If the old frame was a different size, or the existing lining has to change, the job moves towards the new-opening timings above.
Where the extra days go
Most of the time beyond the roof is the finish inside. Once the unit is in, the lining is formed, insulated and boarded or plastered, then left to dry before it is decorated. A skim of plaster needs a day or so to go off before it takes paint, and lime plaster in an older house takes longer. Plaster that is painted too early can flash or blister, so the schedule leaves the drying time in rather than hurrying it.
A splayed lining adds finishing work, because the angled faces are built up and beaded individually. If the ceiling is lath and plaster, the cut and the making good are done with more care and more time. Our answer on fitting a skylight in a lath and plaster ceiling covers what that involves.
Structural work can add days as well. A wide opening in a flat ceiling may need the ceiling joists trimmed, and a lantern needs a kerb built and insulated before the glass arrives.
What else changes the timing
- Access. A roof reached from a clear drive is quicker than a terrace with no room for a tower. Scaffolding, where it's needed, is usually put up before the work starts.
- Roof covering. Plain tiles and slate take longer to lift and re-lay neatly than interlocking tiles.
- Delivery of the unit. Standard sizes arrive sooner than made-to-measure or electric ones, and lantern glazing is made to order.
- Weather. Rain doesn't stop work on the inside, but the roof opening is only left exposed while the weather allows.
- What is found. Old roofs sometimes hide rotten battens or rafters, which need dealing with before the new unit goes in.
Planning the days around the room
The room under the opening is the one that is disrupted most, so it helps to know the order. Furniture comes out or is covered on the first morning, the roof work happens above and around, and the finishing follows once the unit is sealed. In a kitchen, the worktops and appliances nearest the opening are protected. In a bedroom or landing, the room is usually usable again after the roof stage, if less tidy than before.
The finish schedule that comes with the quote sets out the sequence for your room, so you know which days are roof days, which are plastering days and when the paint line is done. If your timing is fixed, for a party or a visitor, say so when you ask for a quote and the order of work can be built around it.
How long before you can paint
A lining that is plastered is touch-dry within a day or so, but a mist coat and a final colour usually wait until it has dried properly. A board and tape finish dries faster than a wet plaster one. Whether you want the lining handed over ready for your own paint or decorated by us, the quote paperwork records the choice, so nobody has to guess at the end.
For the mess side of the same days, see how much mess fitting a rooflight makes. If you're comparing rooflights and roof windows first, our guide to skylight or rooflight, what's the difference helps, and the full inside sequence is in how a rooflight is finished inside.
To get a timeline for your own roof, ask for a quote. We'll survey the roof and ceiling, then give you the days in writing alongside the finish schedule.