How long does a roof lantern take to fit?
One to two days on site once the kerb is ready. The wait before that is manufacturing.
Part of our Roof Lantern Installation guide
The fitting is short. The wait is the manufacturing.
Lead time
Made to size lanterns are manufactured to order, typically three to five weeks from the point the size is confirmed. That confirmation comes after the survey, and on a job with a steel it comes after the steel is designed and in place, because the steel position sets the kerb.
On site
A single lantern onto a sound existing kerb: usually one day. The unit is set, fixed, sealed and the covering terminated.
With a new kerb: add a day, sometimes two, depending on whether the roof covering has to be disturbed and made good around it.
Forming a new opening in a finished roof: longer, and the sequence matters. The opening is formed, structure installed, kerb built, covering dressed and terminated, then the lantern set. Several of those steps need to cure or be checked before the next.
The internal finish
Plastering and decorating the reveal is separate, and it usually happens a few days later once everything has settled. Where we form the reveal, we splay it if the depth allows, because a splayed reveal throws noticeably more light into the room.
What we will not do
Leave a roof open overnight. Whatever stage the job has reached, the roof is made watertight before we leave, every day. If the weather is against us we reschedule rather than work through it badly.
Usually about a week
On an existing extension, a roof lantern installation typically runs to five working days. On a new extension being built, the lantern itself goes in within a day or two because the kerb and the structure are already prepared as part of the build.
The difference is almost entirely the kerb and the structural work.
What the week consists of
Opening formed and trimmed. A lantern is heavy and the opening has to carry it. In an existing roof this means cutting joists and installing a designed trimmer, which is engineered rather than judged on site.
Kerb built. At least 150mm of upstand, square and level, with rigid insulation on the outer face and the deck falling away from it so water cannot pond against the base.
Covering dressed. The roof membrane is dressed up the kerb and terminated correctly. This is the weathering, and it is done before the lantern rather than after.
Lantern set. Frame positioned, levelled, fixed and sealed to the kerb, then glazed. On a larger lantern this needs several people or mechanical assistance, because the glass is heavy.
Internal finishing. Reveal formed, plastered and made good, with drying time before decoration.
What can extend it
Correcting the fall. Where the existing flat roof has no fall, or falls toward the opening rather than away from it, that has to be put right locally around the kerb. It is part of the job rather than an optional extra and it adds time.
Getting it there. A large lantern cannot be manhandled. Crane or glass robot access, and a route to the roof, have to be established before anything is ordered, and arranging a lift is a scheduled event rather than something done on the day.
Weather. An open roof is not left uncovered overnight, and a lantern opening is a large hole. We will not start forming it if the forecast will not allow it to be closed and made watertight the same day.
Lead time, which is the real wait
Lanterns are manufactured to your dimensions. Several weeks is normal and a large or unusual configuration can be longer.
Where a structural engineer is involved, the drawing comes before the order rather than alongside it, because the opening dimensions depend on the trimmer design.
The sensible sequence is survey, structural design, order, then book the fitting to the delivery date. Booking the fitting first and hoping the lantern arrives is how these jobs slip.
What we need before booking
Confirmation of the structural design where a trimmer or steel is needed, a confirmed delivery date for the lantern, and where a crane or glass robot is required, a booked lift and an agreed route to the roof.
All three have to be in place before a fitting date means anything. Booking the week and hoping the lantern arrives is how these jobs slip.
Ask us
Send a photograph showing how the flat roof meets the house and a rough measurement of the room below. We will not price a lantern without a survey, and we will tell you before one whether the project is viable.
Living with it while the work happens
The room below is out of use for the week and it is sheeted rather than merely covered, because forming an opening in a ceiling produces a great deal of dust. The roof is made watertight at the end of each day rather than left open, and we will not form the opening at all if the forecast will not allow it to be closed the same day.
One last point
On a new extension the lantern goes in within a day or two, because the kerb and the structure are prepared as part of the build. Almost the entire difference between that and a week is retrofitting into a roof that was not designed for it.
The lantern itself
Assembling and setting a domestic lantern onto a prepared kerb is typically a day for a competent crew, sometimes less on a small unit and more on a large or heavily divided one.
That assumes the kerb exists, is square and level, and the survey was taken from it.
Everything before that
Which is most of the programme.
Structural design and the steel. Then the opening formed and the kerb built and insulated. Then the waterproofing dressed up the kerb. Then the survey to the finished kerb, and only then the order.
On an existing extension, add correcting the roof fall if it is inadequate, because a lantern kerb on a roof that ponds is a problem from day one.
The lead time
Several weeks from order for a straightforward lantern, longer for a large one or an unusual configuration. Every lantern is made to your dimensions, so there is no stock to draw on.
Afterwards
Making good internally, plaster drying before decoration, and the ceiling realistically repainted rather than patched.
And access: mechanical lifting where the panes are too heavy to carry through the house, which needs a route and a standing position arranged in advance.
More on Roof Lantern Installation
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