The short answer
On a new extension, the lantern is usually lifted and glazed within a single day once the kerb is ready. On an existing flat roof the kerb has to be built first, so the work takes longer and may run into a second day. The exact length depends on the lantern's size and weight, the kerb, the covering and the weather, and the written job plan sets the days out before you commit to anything.
A new extension against an existing roof
The biggest single factor in how long it takes to fit a roof lantern is whether the opening and the kerb are already there. On a new extension the roof is framed with the lantern in mind, the kerb is part of the build, and the fitting day is mostly about lifting the lantern into place and making it weathertight.
On a finished flat roof the day also contains cutting the opening, trimming the joists and building the kerb. These stages are laid out in the retrofit route in detail. They happen in sequence, each one right before the next begins, so a retrofit is the longer job.
Size matters on either kind of job. A compact square lantern on a garden room is a lighter lift than a long rectangular one over a kitchen, and the crew, the lifting aid and the time set aside follow from that. The measurements are already in the plan at survey, so the day is sized to the unit and not guessed.
How a fitting day runs
The morning starts with access. Scaffold or a safe working platform is up, the lantern has been delivered and checked against the plan, and the room below is protected. Where a kerb is to be built, that comes first, with the covering turned up its face.
Then the lantern goes on. A large one is heavy, so it is lifted by several people or with a lifting aid, set on the kerb on its seal, checked for level and square, then fixed. The glazing is inspected, any opening vents are tried, and the outside trims are finished.
Timing within the day is planned too. The lift is done when the crew is fresh and the light is good, the glazing check comes straight after, and the weathering work is left with several hours in hand. A lantern that goes on at the end of a long afternoon is a lantern that has been rushed, so the plan starts early and leaves the close of the day for finishing, tidying and a walk round with you.
- Access in place and the room below protected
- Kerb built, or checked against the surveyed size
- Lantern lifted onto the kerb and fixed
- Glazing, vents and trims finished
- Roof closed and weathertight before the team leaves
Making good inside
Indoors, the underside of the opening needs a neat finish. That might be plasterboard reveals, a lining or a window board, depending on how the extension was built. Where plastering is needed it is booked as its own step, because wet plaster has to dry before it can be decorated.
The plan says who does which part, so there is no gap between the roof being closed and the room looking finished. Dust control and a clear-up belong to the day, and the area is left tidy.
Finishing indoors can follow the roof by a few days. Once the lantern is weathertight, the reveals are lined and the plaster is allowed to dry, and decorating comes after that. A fitting day is therefore the end of the roof work and not always the end of the whole job, and the plan separates the two so you know when the room will be fully usable again.
What can push a job into a second day
Some causes are known at the survey and written down. Others only show once the roof is open. A large or heavy lantern needs more time for a safe lift. A kerb that needs more building than expected, or joists in a different state from what the survey showed, adds work. Weather can stop roof work too, since a covering cannot be laid or joined onto a wet surface.
None of this is unusual, and the point of a plan is that it makes room for it. We would rather book two days and finish early than promise one and leave a roof open.
If a second day does become necessary, the roof is made watertight at the end of the first, with the kerb covered and the lantern either fixed or safely held. You are told what will happen the next morning, and the room below stays protected overnight. A second day is therefore a planned continuation and not a break in the work.
| Factor | Effect on the schedule |
|---|---|
| Retrofit rather than new build | Opening, trimmers and kerb added to the day |
| Large or heavy lantern | A slower, safer lift and positioning |
| Covering tie-in | Needs dry conditions |
| Internal finishing | Plastering and decorating follow on |
| Weather | Roof work waits for a dry spell |
How the plan allows for the extra time
The fitting day, or days, is agreed at the point the lantern is ordered, and appears on the plan beside the delivery lead. Made-to-measure lanterns take weeks to build, so the date is set around delivery. If a second day is likely, it is booked straight after the first and not left to be arranged later.
If weather moves the date, we tell you and rebook the roof work for the next suitable day. Nothing is left open: the roof is always closed before the team goes home.
The work that comes before the fitting day
The preparation matters as much as the day itself. The survey fixes the sizes, we look up the council position for your address, and the Building Control notification is made where the work is notifiable. The first of those is covered in the lantern planning answer, and the structural side of the opening is in timber or steel for the opening.
A steel beam, if the engineer specifies one, arrives with the lantern so that both are on site together. Nothing should be waiting for a delivery on the morning of the fit. Calling the day off at the last moment is far more disruptive than a short delay at the ordering stage, which is why the date is only fixed once the lead times are confirmed.
The roof lantern installation page shows a complete job in order, and each fit is backed by a written ten-year guarantee on our workmanship.