Can a Roof Window Be Fitted From Inside?

A roof window sits in the plane of the roof. Its frame is fixed to the rafters, and a flashing kit wraps the frame so rain runs over the sides and down onto the covering. That flashing tucks under the tiles or slates above and sits over them below. All of it is outside work.

Slate and tile have to be lifted around the opening, then relaid on the finished flashing. Doing that from the loft is possible only for a few tiles at the edge, and it risks cracking the covering by working at an awkward angle. For a new opening, the rafters also need cutting and trimming from above and below.

Think of it as two layers. The inner layer is the frame, fixed with brackets to the rafters and sealed against the loft side. The outer layer is the flashing and covering. The inner layer can be touched from inside, but the outer layer cannot be built from below.

Some sales talk plays on this, promising a quick fit with no one on the roof. A window cannot be made watertight by working on only half of it.

There are a few situations where more of the job can be done indoors.

• Glass only. If the frame is sound and the double glazing alone has gone, the new glazing can be changed without a new frame. Changing just the sealed glass in an existing frame generally falls outside notifiable work.
• Same-size swap. A matching unit in the same opening can sometimes reuse the existing flashing, but that depends on the age and condition of what is there.
• Interior finishing. The lining, insulation and plaster reveal inside are always inside work.

Even then, we normally go onto the roof to check the flashing and the covering around the opening. Leaving the outside unchecked would mean fitting a new unit into an old weak point. Where glass alone is the issue, misted and failed rooflights explains the replacement route.

On a Georgian house in Bath or Clifton with natural slate, we are extra careful. Old slate can be brittle, and lifting it from below risks cracking the neighbouring ones. That is a good reason to work from the roof, with a roof ladder spreading the weight.

If someone suggests an inside-only fit to save on access, ask three things: how will the flashing be changed, how will the roof covering be relaid around the frame, and how will the roof be left weathertight at night. A good answer names the steps. A vague answer is a reason to compare quotes.

Access still needs thought. A tower or scaffold is not always needed, since a low rear slope can be reached with ladders and roof ladders. A steep or high slope on a Victorian terrace often needs more. The effect on price is covered in roof window fitting cost.

Weather matters too. A wet or windy day can stop roof work, and a careful team will move the date rather than leave an opening exposed. Building that flexibility into the booking is sensible.

One more check is worth making: ask who does the plaster and decorating of the reveal. Some quotes finish at the frame, leaving a bare lining for you to deal with. Ours says plainly where our work ends.

The result is a unit that is fixed from within, sealed from without, and tidy where you see it every day.

Our method keeps the disruption indoors small. Floors and furniture below the opening are protected before any work starts. The roof is made weathertight by close of play each day, so a half-finished opening never sits open overnight. One team handles the roof, the frame and the lining, so nobody waits on another trade to turn up.

Whether the job is a new window or a replacement, a free survey comes first. We look at the covering, the rafters and the attic side, and the written quote says what will be done indoors and what outdoors. A whole new unit in an opening is notifiable work and the notification is ours to make. You can read about the full range on the roof window installation page.

After the unit is in, we line the opening, tidy the reveal and show you how the sash works, including any vent bar for overnight air.

Ask for the order of work in writing, so you know which day the roof is open and which day the plastering happens.