Roof window installation in a tiled roof, so the roof looks untouched

The work starts on the ground and in the loft, because what lies under the tiles decides how the window is fitted. A roof window is not bolted onto the outside. It is built into the roof.

From inside, we look at the rafters: their size, their spacing and their direction. The window wants a clear opening between them, or a trimmed one, and the choice sets the size of the window we can offer. Our page on standard roof window sizes and rafter spacing explains that fit. From outside, we look at the tile type, its condition and its lap. A sound roof of plain clay tiles behaves differently from one of concrete interlocking tiles, and an old roof of brittle tiles is handled more carefully than a recent one.

We also check the pitch. Every roof window has a range of pitches it is made for, and a flashing kit is matched to the pitch. The limits are covered in roof pitch and roof windows. All of this goes into the written plan, along with the flashing and the tile reuse, before work starts.

The sequence below is the core of the answer. Each step is small, and each one has a reason for where it sits in the order.

1. Mark the opening. The position is set out from inside, then transferred to the outside with a tile at the edge of the patch chosen to keep the courses tidy.
2. Strip the tiles. Tiles are lifted from the patch and from a few courses above, where the flashing will run under them. They are stacked carefully, because we reuse them.
3. Cut back the felt and battens. The membrane is cut to the frame line and folded back. The battens are cut to the opening and trimmed to the width the flashing needs.
4. Frame and fix the window. The rafters are trimmed where the opening requires it, a new timber border is fixed, and the window goes in at the chosen height from the ridge.
5. Dress the membrane. The felt is lapped onto the window frame and sealed to it, so water running down the roof is steered round the opening, not into it.
6. Fit the flashing kit. Pieces go on from the bottom upward, so each one laps over the last.
7. Relay the tiles. The tiles go back in courses, cut where they meet the flashing.

The order matters most at steps five and six. Water sheds downhill, so every layer must overlap the one below it. A flashing fitted the wrong way round might look fine on the day and fail in the first hard winter.

This is the part of the job that keeps the house dry, and it varies with the tile. The flashing is a set of pieces for the bottom, the two sides and the top of the frame.

For tiles with a pronounced profile, such as concrete interlocking tiles or pantiles, the side pieces are made to follow the ridges of the tile, so there is no gap beneath them. For flat tiles and slates, the sides are built up with soakers, small pieces of metal that lie between each course and turn up against the frame. In both cases the top piece tucks up under the tiles above, and the bottom piece lies over the tiles below. We go through the detail of each in roof window flashings for tiles and slates explained.

A correct flashing kit is made by the window's manufacturer for the window and the tile profile. Using one that matches is what keeps the fit predictable, and it is part of why we choose the product before the day. The brand question has its own page: comparing roof window brands.

A neat result is the point of relaying the tiles rather than patching in whatever comes to hand. The roof should look as though the window was always there.

Because the tiles were stacked in order, the same ones go back. Tiles that cut across the flashing are trimmed to fit, and the course lines are kept straight, so the window reads as one clean rectangle in the pattern. Any broken tile lifted during the work is swapped for a matching one rather than reused. On an older roof, the exact colour match of weathered tiles is worth attention, and where the roof is in a conservation area we check whether the planning position affects a window on the front slope before anything is ordered. Rules differ by address, which is why that check is made for each one.

Inside, the work is finished with a lining that ties the window to the sloping ceiling. The plasterboard splay, the insulation and the finish are covered on our page about roof window linings and making good the reveal.

A roof window is usually over a bedroom, and a tiled roof already muffles weather better than a flat roof does. The window is still the thinnest part, so we specify it for the room.

The glazing is the first choice: laminated glass, with a thicker outer pane or an acoustic build, is what calms rain and aircraft overhead. The flashing is the second, because a loose or badly bedded piece of metal can tick in the wind. Both go into the quiet spec that comes with every quote, and the glazing options are covered in acoustic glazing options for roof windows in loft bedrooms.

The work is installed to current Building Regulations, we handle the Building Control notification where it is notifiable, and the install carries our 10-year workmanship guarantee, set out on our guarantee. To have a window planned for your roof, get a quote. The whole service is on our roof window installation page.

How long does the roof stay open?

Only for the part of a day that the work needs. The felt and flashing go on as the window goes in, and the opening is weathered the same day, before we leave the roof.

Will my tiles be damaged?

Sound tiles lift and relay without harm. Old, brittle tiles can break, which is why we check them first and keep spare matching ones on hand rather than use a mismatch.

Does the window need its own gutter or channel?

Where a roof window sits on a single line of rafters, a flashing kit carries the water past it. A wider combination or a window that blocks a long run of water may call for a back gutter above it. We decide at the survey.

Can the window be fitted by someone with a ladder and a weekend?

It is possible, but the flashing and the weathering are where amateur work goes wrong. Our page on whether a roof window should be fitted by a professional goes through it fairly.