The short answer
A new rooflight in a roof that has never had one usually takes one to three working days on site, most of it on the structure rather than the glass. A single roof window in a pitched roof sits at the short end. A large flat rooflight or a roof lantern sits at the long end, because the opening has to be framed, insulated and weathered before anyone fits the unit.
Why a new opening is slower than a swap
Fitting a rooflight where none existed means building the hole as well as filling it. That is the part that takes the time.
When an old unit comes out, the opening is already there. The rafters or joists have been trimmed, the upstand or flashing has a history, and the new unit is sized to suit. A brand new opening starts with a solid roof. Tiles or membrane come off, a rafter or two is cut, and the load they carried has to go somewhere. A trimmer goes in on each side, fixed so the cut timbers bear on it. Only after that does the roof begin to look like a place for glass.
The glass itself is the quick bit. A roof window drops into its bracket in minutes. The day is spent on everything around it. If you are weighing a swap against a fresh opening, our page on how long it takes to replace a skylight covers the shorter job.
The sequence, from first cut to last bead
The order matters more than the speed. Each stage has to be dry and sound before the next one closes it in.
- Protect the room. Floors and furniture are covered, and the ceiling below is marked out from the loft or from inside before anything above is touched.
- Open the roof. Tiles, battens and felt come off, or the flat roof covering is cut back to the outline of the opening.
- Frame the opening. Rafters or joists are trimmed and headers and trimmers fixed. On a flat roof, a timber upstand or a prefabricated kerb is set on top and fixed down.
- Weather it. Flashings or a new waterproof membrane are dressed up and over the upstand. This is the stage that has to be finished before the light goes or the forecast turns.
- Fit the unit. The roof window, the flat rooflight or the lantern is lifted into place, levelled and fixed.
- Seal and insulate. Cavity gaps are filled with insulation and the seals at the frame are checked, so warmth and sound stay where they should.
- Line the inside. A reveal is formed in plasterboard from the ceiling up to the glass, then taped and filled ready for decoration.
That is the whole list, and none of it can be skipped to save a morning. The work at stages two to four is what people mean when they ask about timing.
What different rooflights take
The type of unit sets the pace, because each one asks for a different amount of framing and finishing.
| Rooflight | On site | What takes the time |
|---|---|---|
| Roof window, pitched roof | About a day | Trimming rafters, flashing kit |
| Flat rooflight, small | One to two days | Upstand and waterproofing |
| Flat rooflight, large | Two to three days | Bigger opening, lifting glass |
| Roof lantern | Two to three days | Kerb, bars, crane or hoist |
| Sun tunnel | Half to one day | Tube run through the loft |
Those are general ranges for straightforward access, not promises. A survey turns them into a programme for your roof. The size of the opening is the largest single lever, and our guide to sizing a rooflight for the room shows how that choice is made.
What stretches a job
Most overruns come from things that can be found out in advance. That is why the survey looks at them first.
Weather comes first. A roof that is open overnight is a risk, so the work is planned to close it in within the day, and a wet forecast moves the start. We cover that in whether a skylight can be installed in the rain. Access is next. A long carry through a terrace, a steep approach or a roof that needs scaffolding adds hours, as our page on scaffolding for a skylight explains.
Structure is the third. If a rafter carries more than expected or the roof turns out to be built differently from the drawings, the framing takes longer. Where the opening is large, an engineer may need to size the beam, which is set out in does a rooflight need a structural engineer. That work happens before the day, not during it.
The hours you notice indoors
The work above is on the roof, but the room below is part of the job. It is worth knowing what living through it is like.
Expect noise during the opening stage, when timber is cut and fixed. It is at its loudest in the first half of the first day. Dust is contained with sheeting, and the room is left usable at the end of each day, with the roof either finished or closed in. The plasterboard reveal goes in near the end, and the decorating follows once it has dried. A new opening can also mean a new ceiling line, which is why the tidy finish inside is a stage in its own right. Our answer on whether replacing a skylight damages the ceiling goes through that part in detail.
One more thing that adds time, and is worth the hour: the written quiet spec. At the survey we listen for aircraft, road or rain, then set the glazing build, seals and upstand in writing. That happens before the booking, so it never holds up the day itself. The page on the quiet spec shows what it contains.
Questions about timing a new rooflight
Can the job be done in a single day?
A roof window in a pitched roof often can, where access is easy and the rafters need only a simple trim. Anything with an upstand, a kerb or a lantern needs more than a day to frame, weather and finish properly.
Is there a best season to have it fitted?
Dry spells make life easier, but the job is planned around the forecast rather than the calendar. Our page on the best time of year to fit a skylight weighs the seasons.
Does Building Control add delay?
The notification is handled by us and runs alongside the work, so it does not hold the fitting days. A new opening in a roof is covered on our page about Building Control for a new rooflight.
Does a bigger rooflight always take longer?
Generally yes, because the opening is larger, the structure heavier and the unit harder to lift. Two smaller units can take a similar time to one large one, so the number of openings matters as much as the size.
For a programme written around your own roof, get a quote. The wider service is on our page for skylight and rooflight installation in Crawley, and the guarantee covers the finished workmanship.