The short answer
Partly. A good deal of the work happens indoors: trimming timbers, fixing the frame brackets and finishing the lining. The outer edge of the window is different. The covering around the frame and the flashing that seals it must be lifted and relaid from the roof, so someone has to be outside, whatever the room looks like. Only some like-for-like swaps keep that outside work small.
Working from the loft saves mess in the room below. The weatherproofing still happens on the slope, and a roofer needs safe access to it.
What gets done from inside
Indoors, the job starts at the rafters, the angled timbers that hold up the slates or tiles. For a new opening, one or two rafters are cut back and a short cross-timber, called a trimmer, is fixed across the gap to frame the hole. Brackets go on the window frame, a lining goes around the opening, and the plasterboard and decorating follow.
Can a swap be finished from the loft?
When an old window comes out and a new one of matching size goes into the same opening, the indoor work is lighter, because the rafters and trimmers are already in place. The old sash can often be unhooked and passed down through the room, and the new one comes up the same way. That is why a straight swap can feel like an inside job.
We still go outside to check the flashing and the covering around the frame before and after. A window that is beautifully fitted indoors but weak at its edges will leak the first time driving rain finds it, and the damp then appears in the lining you have just decorated.
Why the weatherproofing needs the roof
The seal around a roof window is made outside. Slates or tiles are lifted back, the frame is fixed to the battens, the horizontal strips of timber the covering hangs on, and a flashing kit is laid around the frame. Flashing is the set of metal and rubber pieces that carry water past the frame instead of into it. Each piece laps its neighbour in a set order, working up from the bottom edge of the window, and a missed lap is a future leak.
Can that be done by reaching out through the opening?
Not properly. Reaching through the hole means working blind, and a flashing laid by feel is likely to let water in. Lapping a flashing over slates, or under them, depends on seeing every course. Our answer on flashing kits for roof windows shows what goes where.
So a roofer is on the slope for this part, with a roof ladder or a scaffold tower where the pitch demands it. Fitting from inside only is no shortcut that spares the weather side. It is half a job, and the half left out is the half that keeps rain off your ceiling.
When the whole job needs outside access
Some jobs are plainly outside jobs from the start. A new opening in a slope that has never had a window means stripping a patch of covering, cutting the underlay and fitting the frame from above. A larger window than the old one means the opening grows, so the covering around it is cut back too.
Do I need scaffolding for a roof window?
Not always. A window on a low rear slope is often reachable with a roof ladder alone. A window high on a front slope, over a pavement or beside a chimney, is another matter and may need a tower or full scaffold. On Somerset Council ground the scaffold licence is applied for by the appointed contractor, which is why the scaffolder features in the plan from the first visit.
Where a roof window belongs to a loft conversion, there is a second question to settle early: whether Building Regulations apply and what they ask for. Our page on Building Regulations for roof windows sets it out, and the overview of roof windows and skylights covers the rest.
Keeping the room below clean
The usual reason people ask about fitting from the inside is mess. A roof window job makes dust, and some of it falls into the room when the old frame comes out or when plasterboard is cut for the lining.
What protects the room below?
Sheeting over furniture and floors, a clear route for carrying tools, and a dust screen across the loft hatch or stair door all help. We agree the plan with you before work starts: which rooms get covered, which way the waste goes, and who is moving what. Waste leaves with us when the visit ends, instead of stacking up in the garden.
It also helps to clear the space under the window beforehand. Take pictures and shelves off the wall, lift rugs, and empty the area around the opening. If the window is in a bedroom, think about where you will sleep if the lining is still waiting to be finished. Tell your neighbours about any scaffold and noise too, which goes down well. After the survey you receive a written price and a day-by-day plan, so nothing about the visits comes as a surprise.
More on fitting a roof window
Can I take the old Velux out myself and let the roofer fit the new one?
We would rather not leave a hole in the roof between two jobs. Once the old window is out, the opening needs weathering straight away, and the roofer has to check the rafters and trimmers first. Leave the removal to whoever is fitting the new window, so the opening is never left to the weather.
Will the loft lining be finished when you leave?
The lining around the window is part of the fitting, and we agree beforehand how far it goes. Plastering and decorating are a separate stage, so ask what is included before you book. The written price after the survey states the scope for your window.
The full picture: Velux roof window and skylight installation in Taunton ยท More short answers