Roof window fitting time
How long does it take to fit a roof window?
The short answer
It depends on the job, so the useful answer is a range that the survey narrows down. Swapping an old roof window for one of the same size in the same opening is the shortest job. Cutting a new opening in a tiled or slated roof takes longer, because rafters are trimmed, covering made good, the window flashed and the lining finished. Access, weather and indoor finishing all move the time, so the plan goes in the quote.
What makes one roof window go in quickly and another take longer, and the order the work follows from the first tile lifted to the last trim fixed.
A swap and a new opening are different jobs
Replacing a window that is already there means working in a hole that exists. The old window comes out, the frame and flashing are checked, and the new window goes into the same opening. If it is the same size and the flashings are renewed, the structure does not change and the covering is disturbed only close to the frame.
A new opening is a bigger piece of work, because nothing is there to start from. The covering has to be stripped back over an area wider than the window, a rafter or two cut and trimmed with new timbers either side, a border formed round the opening and the covering relaid. Because it alters the structure, a new opening may need approval, and our guide to Building Regulations for roof windows explains when. A loft conversion with several windows takes longer again, simply because more openings have to be formed.
What changes the time on site
The roof covering has a large effect. Interlocking concrete tiles lift off and relay in bulk, while hand-made clay tiles, old slates and stone slates need careful lifting, and breakages are likely on an old roof. A window set into a flat or low-pitch roof has its own detail at the upstand and covering, and that takes longer to form.
Access matters as well. A bungalow reached from a ladder is a different proposition from a tall terrace needing scaffold towers, and if scaffolding blocks a public footway, the scaffold needs a highway licence. West Sussex County Council asks for at least 10 working days between applying and erecting the scaffolding, so the licence can set your start date. Our answer on the cost of fitting a roof window covers what else moves the price.
How the work runs on the roof
On the roof, the sequence is much the same for most pitched jobs. Tiles or slates are lifted over the area, battens cut back, and the opening formed or checked. The frame is secured to the rafters, the underlay is dressed up to it, and the flashing kit fitted from the bottom edge upward, then the covering relaid around it. A sensible plan closes the roof in by the time the crew leaves each evening, so the opening is not left to the weather overnight. If the forecast looks poor, it is better to move the day than to open a roof you cannot close in time.
Weather decides the pace. Wind makes lifting large panes unsafe, and rain in the forecast means more time covering and less time working. A plan agreed beforehand names the fallback for a wet or windy day, and that is better than a promised date. Our guide to replacing an old roof window covers the like-for-like route in more depth, including what to expect when the old frame comes out.
Indoors: lining, insulation and finishing
The roof is only half of it. Indoors, the opening needs insulating round the frame and a lining fitted so the plasterboard returns neatly to the window. If the ceiling is being altered for a new opening, there is also making good, plastering and decorating to come. Those trades can be separate from the roofing, and their time is not always ours to give, so check who is doing what and in which order.
The thermal detail is not optional. Approved Document L 2021 Table 4.2 expects a roof window put into an existing home to reach 1.4 or Window Energy Rating Band B; a frame with poor insulation brings condensation back. A tidy internal finish takes care, and it is the part you look at every day, so it deserves the same attention as the weatherproofing above it.
Questions to put to any roofer
When you ask a roofer how long, ask what the answer includes. Does it cover the scaffold, the plasterer and the clear-up? Has the window been ordered, and how long is the wait for it? Is there a building control inspection to book? A firm that can answer those has thought the job through, and a vague answer is worth probing before you pay a deposit.
We begin with a visit, taking pictures of the roof and the room under it, and the plan then sets out the order of work, who finishes the room and what the fallback is for bad weather. We take the waste away at the end. The quote is written, and its price is one total. Our skylights and roof windows page shows the work we do, and our habit is to explain the job before pricing it.
Related questions
Roof window timing questions
Do I have to be at home while a roof window is fitted?
Someone needs to give access to the room below, and the work makes dust and noise indoors. You do not need to watch it. Access and protection for floors and furniture are agreed before the start, and a walk-round at the end covers the finish.
Does the window have to be ordered in advance?
Usually, yes. Standard sizes may come from a supplier quickly, while made-to-measure or special glazing takes longer. The model and size are confirmed at the survey so the order is right before the roof is opened up.