How Long Does Skylight Installation Take?

Take the simplest job we do: an old roof window in a pitched roof, swapped for a new one of the same size code. The opening already exists, the rafters either side stay where they are, and the new frame fits the gap the old one leaves.

1. Dust sheets go down inside, from the door to the window, and the room below is cleared of anything that could be marked.
2. The old sash comes out first, then the frame, working from inside where the window allows it.
3. A few courses of tiles or slates around the opening are lifted so the new flashing can be dressed under them.
4. The new frame is fixed, levelled and checked for square, then the underfelt collar and flashing kit are fitted.
5. The tiles or slates go back, the sash goes in, and the window is tested through its full opening range.
6. Inside, the lining around the frame is finished and the room is cleaned and handed back.

The opening does not change, so there is no structural work and nothing waits on anyone else. This kind of job can often be done in one visit, with the roof watertight again before we leave.

Each of these adds work to a matched swap, and some add waiting time between stages.

• A new opening. Cutting into a pitched roof means cutting a rafter and fitting trimmers to carry the load around the gap. That is structural work and is slower than refitting a frame into an existing hole.
• A bigger window than the old one. The opening has to be enlarged, which brings the same rafter work as a new opening.
• A lantern or flat rooflight on a new kerb. The kerb is built first, then the flat roof covering is dressed up its sides, and only then does the unit go on. Each stage has to be right before the next.
• Several units on one roof. Each opening is its own piece of work, even when they share the same scaffold.
• Electric opening units. Wiring for the motor and controls adds a stage, and on some jobs it means an electrician's visit.

The survey is where we find these things out. Rafter centres, pitch, the opening size and the condition of the timbers all feed into the time on the quote. You can read what we check on that visit in our answer about the rooflight survey.

A roof is only open while the old unit is out and the new one is not yet sealed. We plan that window of time around the forecast, and a roof is opened only when the forecast for that stretch is dry and calm.

That means the start date can move. If the forecast turns, we call you to agree a new date. Flat roof work is the most sensitive, because the roof covering needs dry conditions to bond properly around a new kerb. A pitched roof window swap is less exposed, as the opening can be covered quickly if a shower arrives.

How we reach the roof shapes the timetable as much as the window itself. Many roof window swaps can be done from inside the room, working out through the opening, so no scaffold is needed. Other jobs need a scaffold tower or a full scaffold, and that brings its own steps.

• The scaffold is booked with the scaffolder, who works to their own calendar.
• It goes up before we arrive and comes down after we finish, often on separate days from the installation.
• Where it stands on the pavement or a shared drive, a licence or a neighbour's agreement may be needed first.
• On a terrace with no rear access, everything has to come through the house, which takes more care and more time.

Our roof window installation page explains which windows can be fitted from inside. For flat roofs, the roof lantern installation page covers the access a lantern usually needs.

Replacing a frame in an existing opening usually needs only the lining around it finished. A new opening needs more. The ceiling or plasterboard is cut, the reveals (the sides of the light well) are boarded, and the surfaces then need plastering or taping and filling, followed by decorating.

Plaster needs time to dry before it can be painted, so this stage often falls after the roof work is finished. Your quote says which parts of the making good we do and which are left ready for your decorator.

Blinds are usually fitted at the end, once the lining is finished, and can be added during the installation visit if they are ordered with the window.

Replacing a whole rooflight or roof window is notifiable, and a new opening needs Building Regulations approval because of the structural work. Neither has to slow the installation itself, but the paperwork has its own timetable.

For a new opening, the application is made before work starts, and an inspector may want to see the trimmed rafters before they are covered. That visit has to be booked, which can set the pace of the job. When the work is complete, the completion certificate follows from the building control body. Our guide to Building Regulations for rooflights explains which jobs need which route.

The quote sets out the time for your job, including any waiting for scaffolding, inspections or drying. If something we find once the old unit is out changes that, we tell you before carrying on.