The short answer
The roofer first protects the room below and sets up safe access. Tiles or slates come off around the opening, the frame is fixed between the timbers, and flashings seal it to the covering. The roof covering goes back, the sash is fitted, and the inside lining is finished. The roof is weathertight before we leave.
Installation day follows an order that does not change: protect, open up, frame, seal, close up, finish inside. Knowing the order helps you plan the day.
Before the first tile comes off
The day starts below the roof. We clear the space under the opening, lay dust sheets over floors and furniture, and run protection up the stairs if that is the route for materials. Loft insulation near the opening is lifted aside and kept dry, ready to be tucked back round the new frame. Access is set up before anyone goes onto the slope, with ladders or a scaffold tower, and a full scaffold where the height or the front elevation calls for it.
Does scaffolding need a licence?
Only when it stands on the public highway, since the permission is a scaffold licence under the Highways Act 1980 s169, given by the council that manages the road. On a Taunton street, Somerset Council says it grants these to accredited contractors only, and the appointed contractor makes the application, on ten working days' notice at £124.60 for each 28-day period (April 2026). Elsewhere the rules differ, so we ask the scaffolder who applies and give you the dates.
We also look at the forecast, since an open roof should never meet rain. The start therefore depends on the weather as well as the diary. The main roof windows and skylights page shows how the visit fits into the whole job.
Opening up and framing the hole
With the room protected, the roofer strips the tiles or slates in a patch wider than the window, stacking each one for reuse. Underneath sit the battens, the thin timber laths the covering hangs on, and the underlay, the waterproof sheet under those. Both are cut back to bare the rafters.
Does the roofer cut a rafter?
It depends on the window and the spacing of the rafters. Where the new frame fits between two rafters, none is cut. Where it is wider, a rafter is cut and new timbers, called trimmers, are fixed across the gap to carry the load round the hole. That is structural work, and your building control body may need to see it, so we raise it in the survey. The opening is then squared up and checked before the frame goes in.
This is the point where the day can change shape. A surprise such as a damp rafter or an old repair is dealt with there and then, and we show you what we find and what it means for the price before going further. Our answer on fitting a Velux from inside shows another way in.
Fixing the frame and sealing it
The window frame is lifted into the opening, levelled, and screwed to the timbers with the brackets supplied. The flashing kit follows. This is a set of metal and sheet components that sit around the frame in a set order, starting at the bottom edge and working up, so each piece overlaps the one below and water is carried over the joints.
Why is the flashing the part that matters?
The glass is made in a factory and arrives sealed. The weakness in a roof window is the junction between the frame and the covering, which is made on site. A kit fitted wrongly, or in the wrong order, lets water in at a corner. Our page on the Velux flashing kit explains the parts and how the kit is chosen for your tiles or slates.
The underlay is dressed into the frame so any water that gets past the covering runs out and does not soak the timbers. Then the tiles or slates are refixed round the flashings, with any broken ones replaced to match. At this stage the roof is weathertight again, and the window is in.
Hanging the sash and finishing inside
Once the frame is fixed and sealed, the sash goes on. The opening glazed part is hung, the handle checked and the seals tested. If you ordered a blind, it can go on now. Some windows come with a fitted insulation collar and a lining kit that finishes the deep sides, called the reveal.
How does the room look when we leave?
The lining forms the neat splayed surface inside the room, joining the window to the ceiling and wall. We fit it, tape the joints, and leave it ready for paint. Decorating is yours unless agreed otherwise. We clear the dust sheets, take waste away and leave the room as we found it, apart from the new window.
You should expect an explanation of how to open, close and clean the sash, plus the data sheet for your records. For how long the job takes, our page on how long a Velux takes to fit is the place to look. Send us photos of the room and the roof, and the survey and the written price will spell out what your day involves.
More on fitting day
Do I have to be in while the window goes in?
Someone should be there to let us into the room, answer questions and see the finished window before we pack up. You do not need to watch the work. We tell you each morning what the plan is, and each evening what has been done.
What if it rains while the roof is open?
We plan the start around the forecast and keep tarpaulins and sealed sheeting on site. If rain comes, the opening is covered and made watertight until the work can continue. A good survey reduces the risk, but weather is the one thing a roofer cannot book.
The full picture: Velux roof window and skylight installation in Taunton · More short answers