Most roof lantern installations take two to four days on site. A like-for-like replacement onto a sound existing upstand is a two-day job: strip and weather in on day one, lantern set and glazed on day two. A new opening cut into an existing flat roof runs three to four days because of the structural framing. Large-span or multi-section lanterns take four to six days. Add three to five weeks of manufacturing lead time before any of that starts.
Those figures are working days on site with the scaffold or tower already up, and they assume the roof structure is sound and the weather is workable. The number people actually care about is different: how long is the roof open? On a replacement, hours. We strip in the morning and the opening is weathered in and watertight the same afternoon. We do not leave a roof open overnight.
The three programmes
| Job type | Days on site | Roof open for | Main variable |
|---|---|---|---|
| Like-for-like replacement, sound upstand | 2 | Half a day | Condition of the existing upstand |
| Replacement with upstand rebuild | 2 to 3 | One day | Extent of timber decay found |
| New opening, existing flat roof | 3 to 4 | One day | Structural framing and engineer’s detail |
| New extension, opening formed as built | 1 to 2 | Not applicable | Coordination with the main contractor |
| Large span or multi-section | 4 to 6 | One to two days | Craneage, sectional assembly, glass weight |
The new-extension case is the quickest and the cheapest, because the opening is designed into the roof rather than cut out of it afterwards. If you are building an extension and a lantern is anywhere in your thinking, decide before the roof deck goes down. Retrofitting the same lantern six months later is a materially different job.
The bit before site: lead time
Aluminium lanterns are manufactured to your surveyed kerb dimension, not picked off a shelf. Standard sizes in a standard RAL colour typically run three to five weeks. Dual-colour finishes add a week or so, because the profile goes through the coating line twice. Marine-specification coating for coastal work adds a similar amount. Timber lanterns, and conservation-style units for listed properties, run six to ten weeks and sometimes longer.
We do not open a roof until the lantern is physically in stock. That rule sounds obvious and it is routinely broken, usually with a sheet of polythene and an apology attached. Nothing starts on site waiting for a delivery.
What extends the programme
- Structural work. A ring beam needs an engineer’s calculation first, and on anything over about 1.5m across you will need one. Allow one to three weeks for the design, plus Building Control’s involvement on retrofit work. This is the single biggest source of delay and it happens before we get anywhere near the roof.
- Upstand decay. Lift a twenty-year-old lantern and the timber underneath is frequently wet. Rebuilding an upstand properly adds most of a day. We photograph what we find and show you before we go further.
- Weather. Membrane adhesives have minimum application temperatures and none of them bond to a wet substrate. Sustained rain stops the weathering-in stage, and we sheet down and return rather than pressing on.
- Craneage. Above roughly 3.0 x 2.0m you are often into a crane lift or a sectional lantern with a structural spine. Crane hire is a booked slot, so it fixes a date in the programme that everything else has to work around.
- Plaster drying. Internal reveals need to dry before decoration. That is on your programme rather than ours, but it is why the room is not finished on the day we leave.
Weather stops work; it does not extend the roof being open. If conditions turn during the strip, the opening is sheeted, battened and secured before anyone leaves site. Coming back on a better day costs a day. Carrying on in driving rain costs a ceiling.
Suffolk and north Essex timing
Coastal work at Felixstowe, Harwich, Frinton and Aldeburgh carries more weather-lost days than inland Suffolk, particularly between November and February when a north-easterly makes working on an exposed flat roof unsafe rather than merely unpleasant. We build that into the programme rather than promising a date we then miss. Marine-specification coating also adds to the lead time, so a coastal job wants planning further ahead than an equivalent one in Stowmarket.
Conservation and listed work across Lavenham, Dedham, Southwold, Coggeshall and central Ipswich runs on a different clock again. Listed building consent takes eight to twelve weeks in practice, and a conservation-style timber unit will not be ordered until consent is granted. Start that conversation with the conservation officer months before you want the work done.
Related questions
- What time of year is best for fitting a roof lantern? goes into seasonal planning.
- How is a roof lantern fitted to a flat roof? sets out what happens in each of those days.
- How much does it cost to replace an existing roof lantern? covers what upstand remediation adds.
More detail is on our stage-by-stage fitting process page and, for the bigger units, large-span and multi-section roof lanterns. Both sit under roof lantern installation.
Get a date and a fixed price
We survey first, then give you one written price and a realistic programme with the lead time stated on it. Every installation carries a 10-year workmanship guarantee. Request a fixed quote for your property in Ipswich, Suffolk or north Essex.
Thinking about this job? We survey across Ipswich, Suffolk and north Essex and give you a fixed price before any work starts, with a 10-year workmanship guarantee.