How long does a roof lantern take to fit?

The short answer

Three to four days on site for a straightforward lantern into a sound flat roof, plus a plasterer for a day and a drying period after that. The calendar answer is longer and it is the one that governs a date: a lantern is manufactured to your measured kerb dimension, so nothing is ordered until the kerb exists, and the frame and glass then take several weeks to arrive. From first email to finished ceiling, a typical domestic lantern runs to a couple of months, most of which is lead time rather than work. What lengthens the days on site is almost never the lantern itself: it is what the existing roof deck turns out to be. The full sequence is on the roof lantern installation page.

Days on site against weeks on the calendar

Two clocks run at different speeds and confusing them causes most of the frustration. The first is site time, which is the crew actually working: usually three or four days for the lantern, one for the plasterer, and a return visit for any electrical work. The second is calendar time: survey, then a written fixed price, then the kerb built as a first visit or as part of the main visit, then the frame ordered off the measured kerb, then the manufacturer’s lead time.

Where a lantern is going onto a roof that also needs re-decking or re-falling, site time can double while calendar time barely changes, because both happen inside the same lead window.

What happens on each day, and what state the roof is in that evening

Day	Work	State at the end of the day
Before day one	Scaffold or tower erected, loading bay formed if glass is being lifted, room sheeted and units protected	Roof untouched
Day one	Covering opened, joists trimmed and doubled, deck and falls made good, kerb built and insulated	Kerb standing, roof temporarily weathered and watertight
Day two	Waterproofing dressed up the kerb face and over the top, corners formed, junction into the existing covering completed	Fully watertight kerb. Safe to stand in this state for days if weather turns
Day three	Base frame bedded and fixed, hips, rafters and ridge set, everything checked square and level, glass in pane by pane, caps or structural tapes fitted	Lantern glazed and water tested
Day four	Kerb lining insulated and boarded, vapour layer taped to the base frame, reveal formed, actuator wiring terminated	Ready for plaster
Plasterer	Reveal and ceiling junction skimmed	Wet plaster, two to three days drying before decorating

The order is built around one rule: an opening is never started unless it can be closed and made watertight the same day. That is why the kerb and its weathering come before the frame, and it is the reason the sequence cannot be shuffled to suit a delivery date.

Lead times: why nothing is ordered until the kerb exists

A lantern is not a stock item. It is cut, machined, powder coated and glazed to a specific base dimension, and a base ring manufactured square will not sit down onto a kerb that is out on the diagonal. So the order is placed off the measured kerb rather than off a drawing, and drawings and built kerbs agree less often than anyone expects.

Manufacturing runs to several weeks for a standard aluminium lantern in a common RAL colour. A non standard colour adds a powder coating cycle. A dual colour frame, inside and out in different finishes, adds another. Timber and timber cored frames take longer again, and on a listed rear elevation in Cheltenham where a painted timber frame is the condition of consent, the lead time is a scheduling fact to plan around rather than a surprise.

The things that add a day, and the things that add a week

A day: trimming across two joist bays instead of one, an awkward junction into an existing covering, a soil vent pipe that has to be moved a rafter bay across, or wiring for an actuator run back to a consumer unit.

A week or more: a deck found to be wet and needing renewal, falls that have to be re-formed with tapered insulation before any kerb goes on, a warm deck overlay across the whole extension, a steel needed over the opening with an engineer’s calculation and a Building Control approval before the covering comes off, or asbestos cement sheeting on an older lean-to which has to be removed under licence first. Each of those is identified at survey by opening up a small area rather than guessing from below, and each goes into the written notes with its time consequence.

Rain, temperature and the parts of the job that cannot be rushed

Some operations have a weather window and no amount of willingness changes it. Adhesives for EPDM want a dry substrate and an air temperature above about 5 degrees. Torch applied felt needs a dry deck. Liquid applied systems have cure times measured in hours that lengthen sharply as the temperature falls, and applying one in a Gloucestershire November afternoon with dew forming at four o’clock is how a coating fails to bond.

Silicone bedding under a base frame also wants dry conditions to cure properly. So the practical position through the winter is that the carpentry and the kerb carry on and the wet trades wait for a window, which means a January lantern can spread across a fortnight of calendar even though it is four days of work. Booking a job into spring or early autumn avoids most of that.

Scaffold: when it goes up, and how long it stands

On a single storey rear extension a tower or a small scaffold usually goes up the working day before and comes down after the glass is in and the external work is finished, so it stands for the best part of a week. Where glass is being lifted it needs a loading bay, which takes a little longer to erect and needs somewhere to stand.

In the Stroud valleys the scaffold is frequently the longest single item in the programme. At Chalford, Rodborough and Nailsworth, where a house is one storey at the front and three at the back and the access is a shared lane or a flight of steps, components get hand carried in and the erection that takes half a day on a Quedgeley driveway takes most of two. That is measured at survey and priced from what is actually there.

The plasterer, the drying time and the decoration after

Plastering the kerb lining and the ceiling junction is a day. Fresh plaster then wants two to three days before a mist coat and longer before a full paint system, more in cold damp weather. Rushing paint onto plaster that is still dark in patches is how a ceiling ends up flaking a year later.

Decoration is usually the homeowner’s own arrangement or a separate trade, and it is worth knowing that the sides of a lantern reveal show every imperfection because raking daylight crosses them all day. A splayed reveal throws more light into the room; a vertical one is easier to get airtight, and on a kitchen ceiling with a lot of moisture in the air, airtightness wins.

Living in the house while it happens

The house stays occupied throughout. Floors, worktops and furniture are sheeted before anything is cut, and cutting the deck produces a good deal of dust that wants the doors to the rest of the house closed and taped.

The ceiling is open for part of days one and three, and while it is open the room is not usable. Between those, the kerb stands weathered and the room is closed off from the sky by a temporary covering, so there is no period where the house is exposed overnight. A kitchen with a lantern going in over it is realistically out of normal use for the three or four working days plus the plastering, which is worth planning for rather than discovering on the Monday morning.

Booking a date, and what fixes it

The sequence is an indicative range by email from photographs of the roof and the room, then a survey at a time that suits, then a written fixed price itemised so it is clear what is frame, glass, labour, scaffold and Building Control, then a date. The date is set against the manufacturer’s confirmed lead time rather than against a hope, and the Building Control notification is submitted and the inspections booked as part of the job.

That fixed price holds unless the scope changes at the customer’s request, or unless something structural is uncovered that was written down as a risk in the survey notes beforehand. How the two figures work is set out on the costs page, and questions specific to your own roof are best answered by email to info@severnskylightsgloucester.co.uk.