The short answer
Not completely. A roof window has to be weathered on the outside: the flashing, the slates or tiles around it and the junction with the roof covering can only be done from the roof or from scaffolding beside it. What can be done from inside the room is the opening out, the trimming of the rafters, the framing and the whole lining and finish. So "fitted from inside" is true of about half the job, and the half you will look at every day.
What happens on the roof
The window sits in the roof plane, and the roof covering has to lap over and around it in the right order. On a slate or plain tile roof, that means lifting the surrounding slates or tiles, fixing the frame to the rafters or to a trimmer, then rebuilding the covering up to the frame with the flashing kit lapped in as it goes. The order matters: lower flashing over the covering below, side pieces tucked under the covering beside, head piece under the covering above. Water runs down, so every layer has to sit on top of the one beneath it.
None of that can be reached from a ladder inside the loft. Even a window that is slid into place from the room side needs somebody outside to dress the flashing and make good the roof. If a quote says the whole job is done from inside, ask what is happening to the roof covering around the frame.
What is done from the room
Most of the preparation and all of the finish happens indoors. Typically that covers:
- marking the opening against the rafters and checking it against the size of the unit;
- cutting back and trimming the rafters, and fitting the trimmers that carry the load around the opening;
- insulating around the frame so there is no cold gap between window and roof build;
- forming the lining between the frame and the ceiling, straight or splayed;
- boarding, plastering or taping, then the beads and decoration.
If the roof space is a habitable loft room with the rafters already boarded, the opening is cut through the plasterboard and insulation from below. In a cold loft with a flat ceiling below, the shaft between roof and ceiling is built from inside the loft. In both cases the room side is where the work is slow and the dust is made, so that is where sheeting and dust control go first.
Where the two sides meet
The moment the roof is opened is the point of most care. The covering is lifted, the rafter is cut and the window is dropped in, all in one visit, so the weather can be kept out and the room covered while it happens. Anything cut from below is protected before the roof is opened above it, and the room is sheeted so that a slate or a shower of debris cannot land on a bed or a bath.
This is also why the order of work is written down. Our finish schedule records the ceiling and roof build and how the lining is formed, so the person in the loft and the person on the roof are working to the same plan. See how a rooflight is finished inside for what follows once the frame is in.
Do you need scaffolding?
It depends on the roof and the height, not on whether the window is "outside work". Anyone working on a roof needs a safe way to reach it and protection against falling, and the rules on working at height apply to a small job just as they do to a large one. On a low single-storey roof or an extension, a roof ladder and edge protection may be enough. On a two-storey house, or a roof with a steep pitch and a slate covering that must not be walked on carelessly, scaffolding or a tower is usually the sensible way to work.
Some firms advertise a roof window with no scaffolding. That can be fine where the roof is low and safely reached, but it is worth asking how the person on the roof will be protected and how slates will be kept off the ground below. Scaffolding on a public pavement may need a licence from the highway authority, which adds time, so it is raised at the survey and not on the day.
When a window can be swapped from the room
There is one case where much of the work does feel like it is done from inside. Where an existing roof window is being replaced with a new one of the same size, the old frame comes out and the new one goes in on the same opening, and the rafters usually stay as they are. The flashing and covering still have to be refitted from outside, but the indoor work is far lighter: the lining is often kept or touched up rather than rebuilt.
A like-for-like swap of the whole window is still notifiable building work, because the Building Regulations treat windows as controlled fittings that must meet Part L. Where the job needs it, Building Control is notified by us. Leaving the frame alone and changing just the sealed glass unit inside it falls outside the notification rules. See can a VELUX window be replaced like for like for the detail.
What to ask before you book
A quote for a roof window should say who is working where. Four questions are worth putting to anyone you are considering:
- How will the roof be reached, and does the price include scaffolding or a tower if the roof needs one?
- Who forms the lining and finishes the plaster, and is it in the same quote?
- How will the room be covered and the dust controlled while the roof is open?
- Who handles the Building Control notification?
A clear answer to each tells you the job has been thought through from the roof down to the paint line. A vague answer to the second one is the most common reason a new window ends up with a raw, unpainted opening that nobody feels responsible for.
Next steps
If you are thinking about a new roof window or a replacement, a survey is the place to settle all of this. We look at the roof from outside, the ceiling and rafters from inside, and write down how each side will be handled. For the wider picture, read about roof window installation in Exeter, or check how wide a roof window can be between rafters before deciding on a size.
When you want a written quote, use the quote form and send a photo of the room and, if you can, the roof.