The short answer
It depends on the job. Swapping an old window for a new one in the same opening is the quickest, because the rafters and trimmers are already there. Cutting a new opening takes longer, since the rafters are altered and the covering is cut back. The lining and decorating come after the window itself and often make up a good share of the total, so ask what is included.
Fitting time is set by what the survey finds, not by a fixed number. A swap, a new opening and a pair of windows are three different jobs.
A swap in the same opening
The quickest roof window job is a swap. The old sash and frame come out, the new frame goes into the opening, the flashing goes around it, and the covering is relaid. The structure is already in place, so there is no timber work to speak of.
What can make a swap take longer?
Surprises behind the old window. A rotten batten, the horizontal strip the tiles or slates hang on, has to be replaced before the frame goes in. Old flashing may be bonded to the covering and need careful lifting. If the old window was fitted with a different make of frame, the opening may be a little off square, and the rafters need adjusting to suit the new one.
Access can add time as well. Where the slope faces the street, scaffold or a tower has to be erected before the first tool goes up and taken down after the last. We cover the sequence on the day in our answer on Velux installation day. MyJobQuote lists a straightforward swap at around £100 less than a standard mid-range Velux (Sep 2026), which reflects the lighter job.
A new opening in a roof that has none
Cutting a window into a plain slope is a bigger job. The covering is stripped back to make room, the underlay is cut, and at least one rafter is cut and framed with trimmers so the load goes round the hole. The frame is then fixed, the flashing is laid, and the covering is relaid around the window.
Why does a new opening take longer than a swap?
Because there is structural work before the window can go in, and each stage has to be right before the next begins. The opening has to be sized to the frame and checked for square, and the roof must be weathered by evening whatever stage the job has reached. Each stage waits for the one before it, which is why a new opening is never a quick job to rush.
A new opening may also bring paperwork. Whether it needs Building Regulations approval, and whether it sits on a side slope or in a protected area, depends on the house. That is worth settling before a date is fixed, not on the day. Our page on Building Regulations for roof windows explains when approval comes into it, and some jobs wait on a decision before work can begin.
Finishing the lining and decorating
The window is only part of what you see from inside. Around the opening sits the lining, the boxed return that runs from the window frame back to the ceiling, usually plasterboard with a plaster skim and paint. In a loft conversion it may also include insulation behind the board.
Is the lining part of the fitting time?
It can be, and it is the part most often left out when people ask how long a window takes. The frame and flashing are done in the roof, then the lining follows from inside. Plaster has to dry before it is painted, so even a small lining can stretch over several days once the drying time is counted.
That is why it helps to ask who is doing the lining and when. Some customers want the window fitted and the room left ready for their own decorator. Others want the opening fully finished. We agree the extent before work begins, put it in the written price, and tell you what happens on each day. Clear walls, moved furniture and an empty landing all save time, so do as much of that as you can the evening before.
More windows, more days
Two windows are not simply double one. Setting up the access costs the same once, so a pair on the same slope is quicker per window than two separate jobs. On the other hand, the roof is open in two places, and covering both before dark takes longer.
Can several windows be fitted at once?
Yes, though not always in a single visit. We usually take one opening at a time and close it in before starting the next, so the roof is never open in more places than we can cover. A run of windows across a long slope is planned in stages for that reason.
We settle the order of work, the access and the likely number of visits during the survey. We look at the framing, the covering and the room below, then give you a written plan with the price. For a sense of what the work costs in general, see Velux window installation cost. For the wider choices on windows, start from roof windows and skylights.
More on timing a window job
Will the roof be open overnight while a Velux is fitted?
No. By evening the opening is closed in, either with the new window and its flashing or with a temporary cover tucked under the covering. A job that cannot be sealed by evening is not started that morning, and we tell you the plan in advance.
Can I stay at home while the work goes on?
Usually yes, though the room below the window is out of use for the day and dust travels. Cover or move furniture, clear the floor, and keep children and pets well away from the loft hatch or stair. We tell you in advance which rooms we need, so you can plan the day.
The full picture: Velux roof window and skylight installation in Taunton · More short answers