The lantern itself goes on in a few hours. Everything around it takes longer. Forming the opening, building the kerb, weathering the covering up it, and finishing the reveal inside are the work, and on an existing roof that is generally a week rather than a day. On a new extension it disappears into the build programme.
How long a rooflight job takes generally
The variables common to any rooflight are on how long does a flat roof rooflight take to install.
This page covers what is different about a structure that arrives in pieces and is assembled on the roof.
Day one, the opening
Cutting and trimming, and it is carpentry.
The covering and deck come off within the marked area, joists are cut and trimmed into new members either side, and where a designed beam is needed it goes in here.
The roof is protected at the end of this day rather than left open.
Day two, the kerb
Built, insulated and squared.
The upstand is framed from the trimming, insulated on every face and made accurately square and level, because the lantern will only sit properly on a true perimeter.
What it consists of is on what is a builders kerb.
Why square matters so much
Because the lantern is a rigid rectangle.
A kerb out of square by a small amount leaves a gap that has to be packed and sealed at one corner, and that corner becomes the detail somebody worries about for years.
It is checked with a tape across both diagonals before anything else happens.
Day three, the covering
Weathering the roof up the kerb.
The flat roof covering is dressed up the sides of the upstand and terminated so that the lantern frame sits over it, and on felt that is a torched detail, on single ply a welded one.
At the end of this day the roof is weathertight with or without the lantern.
The lantern itself
Half a day on a standard size.
The eaves beams are set and levelled on the kerb, the rafters and ridge go up, and the glass is placed and capped, working round the structure.
It is the part people expect to take longest and it does not.
Why two or three people
Because of the panes rather than the frame.
Sealed units for a lantern are heavy and awkward and are placed by hand onto a structure standing above a roof, which is a job for a team rather than a pair.
Where a lift is needed
Adds a day at the front and a booking to the programme.
Where the panes cannot be carried through the house or across the garden, a lift is arranged, and that has to be scheduled with the delivery rather than the day.
Making good inside
The part that runs on after everybody has left.
The internal reveal of the kerb is boarded, the ceiling made good around it, and then it is plastered, dried and decorated, which is days rather than hours.
It is usually the plaster drying that decides when the room is finished.
Splaying the reveal
Worth doing and it adds a little time.
Angling the internal faces of the kerb spreads the light into the room considerably, and it is done at the boarding stage rather than added later.
Where a building control inspection sits
Between the structure and the covering. Notifiable work is inspected at the point where the trimming is visible, so the programme is arranged around a visit rather than closing up and opening again.
What applies is on do roof lanterns need building regulations approval.
On a new extension
Barely a separate item at all. Where the extension is being built, the opening and the kerb are part of the roof construction, and the lantern goes on when the roof is finished.
That is why a lantern designed in is cheaper and quicker than one added.
Lead time before any of it
The largest single delay and it happens before anybody arrives.
A standard lantern in a standard colour is quick. A bespoke size in a special finish with opening panes is a manufacturing period, and the date follows the delivery.
Ordering after the kerb is built
What we prefer on an existing roof.
Measuring the finished kerb rather than the drawing removes the risk of a lantern arriving to a perimeter that is not quite what the design said.
It adds the lead time to the end rather than the start.
Weather
Matters on two days rather than all of them.
The day the roof is open and the day the glass goes in are both weather dependent, and a job is moved rather than started against a forecast that will not hold.
Wind and glass
A specific reason a fitting day gets postponed.
Large panes are handled above head height on a roof, and a gusty day makes that unsafe regardless of whether it is dry.
Fitting in winter
Entirely normal, with sequencing. The work is arranged so the roof is never left open, and only the plastering afterwards is genuinely season sensitive because of drying.
That is on can you fit a roof lantern in winter.
Two lanterns rather than one
Less than double, and not by much.
Two openings and two kerbs is genuinely twice the construction, though the access, the protection and the setting out happen once.
What is asked of the household
More than for a roof window. The room below is open to the roof for part of the work, so it is cleared and sheeted, and a kitchen is generally not usable during the days the opening is being formed.
What we give you on a lantern
We give a programme rather than a duration, because the question people actually want answered is which days their kitchen is unusable rather than how long the glass takes to go on.
The whole picture is on the roof lantern installation page.
Thinking about this job? We survey across Worthing, West Sussex and the South Downs and give you a fixed price before any work starts, with a 10-year workmanship guarantee.