Short answer: How long to fit a skylight depends on which clock you mean. Swapping one roof window for another of the same size is often done in a day. A new opening in the roof, a new kerb, or plastering and decorating afterwards add days, and a made-to-measure lantern or conservation rooflight has to be made first, which takes weeks before anyone arrives.
Two clocks: lead time and time on site
When people want to know the time a skylight fit takes, they usually mean the days spent on the roof. There is a second clock that starts earlier. Rooflight installation time is lead time plus time on site, and the first is often the longer of the two.
Lead time is the gap between agreeing the job and the day the unit arrives. A roof window in a common size can often be sourced from a maker's standard range without much wait. A rooflight built to your measurements is different. A made-to-measure roof lantern is manufactured to the size of your opening, with its own frame, glass and finish, and conservation rooflights are made in the same way. Expect that to take weeks, and plan the rest of the building work around it.
Time on site starts when we arrive with the unit in hand, and it is the clock that affects your household.
A like-for-like roof window
The quickest job is replacing an existing roof window with a new one in the same opening. The old window comes out, the new frame goes in and the flashing is dressed back into the slate or tile. On a clear day, a pitched-roof window swap is often finished in a single day, including the clear-up.
The words that matter there are like for like. The opening has to be the same width and height, the rafters have to be sound, and the roof covering around the old window has to be in a state that takes a new flashing. If the old frame turns out to be set differently from the new one, or a rafter has to be trimmed, the job can run into a second day. The survey is where we check every one of these points, so the day is planned around the roof as it actually is.
What adds days to the job
Several things stretch a one-day swap, and they are usually known before work begins, which is the point of a survey.
- A new opening cut in the roof
- A new kerb built for a flat rooflight or lantern
- Altering rafters or joists
- Plastering and decorating the lining
- Wiring for electric opening units
A new opening is the biggest step up. Cutting through the roof covering, trimming the rafters and fitting the frame is more work than dropping a unit into a hole that already exists. The structure has to be made good before the window goes in, and the roof has to be closed up again whenever work stops.
The inside matters too. Where the opening is new, the lining has to be formed, plastered and painted, and plaster needs time to dry before it takes paint. The work on the roof may be done in two days while the finishing inside carries on for longer.
Flat roof rooflights and lanterns
Fitting on a flat roof has an extra stage that a pitched-roof swap does not. A kerb, which is an upstand lifting the rooflight clear of the roof surface, carries the unit, and the waterproofing has to run up its sides and tuck beneath the edge of the frame. For a new kerb, the order is fixed: build it, waterproof it, then set the unit.
A roof lantern is the longer end of that range. It is heavy, it often needs a crane or several people to lift, and the glass and the frame have to be set carefully level on the kerb. Fitting a lantern on a new extension takes more than a day, and the lead time before it arrives runs to weeks.
Weather and scaffold
The roof is open while the old window is out. We choose the day with the forecast in mind and cover the opening if the work has to stop, but a long wet spell from the west can push a job back a few days, and we would rather move it than fit in the rain.
Scaffold is the other variable. A single roof window on a low rear slope can often be reached by a roof ladder or a tower. A higher roof, a front elevation on a three-storey house, or a number of units across a slope may need scaffold, which has to be put up before the work and taken down after.
| Job | Before the day | On site |
|---|---|---|
| Roof window, same size | Short for stock sizes | Often a day |
| Roof window, new opening | Short for stock sizes | Longer than a day |
| Flat rooflight, new kerb | Depends on the unit | Several stages |
| Roof lantern, made to measure | Weeks | More than a day |
| Conservation rooflight | Weeks | Depends on the roof |
You can shorten the wait by deciding early. A made-to-measure order cannot start until the size, colour and glass are agreed, and clearing the space under the opening on the day helps too.
For the full order of work, see replacing a skylight or rooflight: the whole job. Cost is dealt with elsewhere, in the cost of replacing a skylight. The paperwork, including the Building Control notification that we take care of, is explained in rooflights and Building Regulations. For the planning side, see planning permission for a skylight. If you want a date that fits your plans, get a free quote and a surveyor will tell you how long your roof will take. The quote that follows is in writing and carries a fixed price.
Timing and dates: what homeowners ask next
Do I need to be at home while the work is done?
Someone needs to let us in and be reachable for decisions, and we need access to the room below the opening. We lay dust sheets, keep to the area we are working in and clear up when we finish.
Can the job be done around my builder's programme?
Yes. On a loft conversion or extension, the rooflight is usually ordered early and fitted when the roof is ready for it, so we work to the main contractor's schedule and tell them what the unit needs.
What happens if it rains on the day?
If the forecast is poor we move the date. If rain arrives part way through, the opening is covered and made weathertight until we can finish, so water does not get into the house.