The short answer
Swapping one roof window for a like-for-like unit is normally a single working day. A larger flat rooflight or a lantern can take a day or two, because the curb, the flashing and the ceiling reveal all need attention. Weather, access, the state of the old frame and any timber behind it decide whether a job finishes on time or stretches.
The day, hour by hour
A replacement follows the same order each time. Knowing the order makes it easier to plan the room and the driveway.
| Stage | What happens | Rough time |
|---|---|---|
| Preparation | Dust sheets, furniture moved, access set up | Early morning |
| Removal | Old glazing and flashings come out | Mid morning |
| Checking | Frame, timbers and curb inspected | Late morning |
| Fitting | New unit set, fixed and flashed | Afternoon |
| Making good | Inside reveal finished, site cleared | End of day |
The times move with the size of the unit. The order does not.
The morning is mostly about protecting the house. Floors and furniture under the opening are covered, and the working area is cleared so nothing is carried through a clean room. Access matters here. A roof window in a loft is reached from the roof slope or a scaffold tower, and our page on whether you need scaffolding to replace a skylight explains when access needs more than a ladder.
The old unit is lifted out with its flashings, and the opening is opened up for a proper look. This is the moment a replacement is either quick or not. The installer checks the rafters or curb, the insulation and the state of the lining, and only then is the new unit brought to the opening.
In the afternoon the new rooflight is set, levelled, fixed and flashed, and the inside is finished so the room can be used that evening. A well planned job is weathertight before anyone goes home.
Size and type set the length of the job
A small roof window and a large glass lantern are different undertakings, even though both count as replacing a skylight.
- Roof window in a pitched roof: the fastest swap when the new one is the same size as the old. A day is a fair expectation, and the roof window installation service is built around that kind of job.
- Flat rooflight or glass pane on a curb: the unit itself may come out quickly, but the curb, the upstand and the roof edge take care. One to two days is sensible, and the detail is on the flat roof rooflight installation page.
- Lantern: heavy glass and a large frame need lifting gear and more hands. Expect two days, and more for a big one. Our roof lantern installation service explains the work.
Changing the size of the opening turns a replacement into a larger job. A bigger unit needs structural thought and a longer visit, which is why putting a bigger rooflight in the same opening is worth reading before you commit.
What stretches a replacement
A day becomes two when something behind the old unit turns out to be worse than it looked from the outside.
Weather is first. Rain does not stop a job if the opening can be covered, but high wind can stop work on a roof or a lifted lantern for safety. A fixed date in winter is less certain than a fixed date in early summer, and can a skylight be installed in the rain covers how wet weather is handled on the day.
Timber is next. Old frames sometimes hide damp, or a curb that has moved, or rafters that were cut short when the original was fitted. Renewing any of this takes extra time, and it is better done now than sealed behind new glass. A failed unit shows signs first, and signs a rooflight has failed lists them.
Finally there is the finish inside. A straight swap leaves the lining intact. A changed size or a damaged reveal means plastering, and plaster needs time to dry before it can be painted. That is why a job that looks finished may still have a second visit for decoration. The page on whether replacing a skylight will damage the ceiling goes into it.
Before the day: what shortens it
A replacement runs smoothly when the survey has done its job and the house is ready.
The survey is where the length is decided. We measure the opening, look at the timbers from the loft where we can, note the roof finish and agree the glass build. That build goes into the written quiet spec, which means the unit that arrives has already been chosen for the room, and nobody is choosing on the day.
Clear the space beneath the opening, including anything on shelves nearby, because vibration shakes dust. Make sure the installer can park and reach the roof. Tell us about any pets or sleeping children, since a loft room will be noisy for a few hours.
Building Regulations also apply to replacement glazing, and we handle the Building Control notification where the work is notifiable. Whether that applies is covered in whether replacing a rooflight is notifiable. Doing it properly adds no time on site.
Our skylight and rooflight replacement across Crawley starts with this survey, and like-for-like or a better unit is decided there.
Questions about replacement timing
Will I be without a roof for part of the day?
No. The opening is covered while the old unit is out, and the new one goes in during the same visit. Good planning means the gap is short and protected.
Can I live in the house while it is done?
Yes. The room beneath is unusable for the day, but the rest of the house carries on. Expect some noise from the roof and some movement through the hall.
How long does a brand new rooflight take compared with a replacement?
A new opening takes longer, because a hole has to be cut and framed. Our page on how long it takes to fit a new rooflight covers that.
How do I find out the time for my own roof?
The survey gives a specific answer for your unit, written into the quote. Get a quote and we will come and look.