Can a roof window be fitted to a slate roof?

A slate roof is one of the flattest coverings there is. That is an advantage when you want a window to look settled in it.

Plain tiles curve and interlocking concrete tiles have deep ribs, and the flashing around a window has to rise over them. Slate does none of that. Each slate is a thin flat sheet, laid in overlapping rows, so the surface is close to a plane. A flashing kit made for slate is therefore shallow: its apron lies over the slates at the sides with very little step up, and the window frame stands only a short way above the roof line.

The effect from the street is tidy. A slate roof with a low-set window reads as one surface, where the same window in a thick tile roof casts more shadow at the edges. On a period house, that matters as much as the watertightness. We go through the kit types for each covering in roof window flashings for tiles and slates explained.

The brand matters less than the flashing you specify for it. Whether the window is a VELUX or another make, the slate kit from that manufacturer is what fits the slate, and the standard tile kit is not a substitute. Our page on VELUX window installation covers that range.

This is where a slate job is won or lost. The slates are fragile at the edges, and they cannot be hammered or levered like tiles.

Natural slate is split from rock, and it is typically only a few millimetres thick. The nail holes are close to the head of each slate, and a slate that is shifted roughly can crack at the hole or along the grain. So the work follows a careful order.

1. The slates in the opening area are lifted one row at a time from the top, stacked in order and kept for reuse.
2. The opening is framed and the window fixed, with the underlay dressed into the gutter channel at the side.
3. The flashing is built up from the bottom, as it is on any covering, with each piece lapped over the one below.
4. The slates come back, cut to fit against the flashing, and are fixed with new nails of a material that suits slate.

Cutting is done with a slate cutter or a slate axe, and with a clean line, not a chipped one. A badly cut edge weathers unevenly and looks rough within a year or two, and it may let water past the overlap it is meant to make. Where the cut slates have to be finished against the kit, they are fixed so they do not lift in wind.

Not every slate roof is the same material, and the difference changes the work. The covering decides how much care is needed and how much new material goes in.

Old Welsh slates may have been on the roof for a hundred years or more, and their nails have often rusted. That makes them weaker at the hole, and some will not survive being lifted. A newer or synthetic covering is more forgiving, though it still has to be cut and fixed properly. At the survey we look at the condition of the slates at the edge of the proposed opening before we agree a position, because a slate that is sound in the middle can be crumbling where it will be lifted.

The exact position also depends on where the courses fall. Our answer on how close to the ridge a roof window can go explains how the gauge of the covering sets the height.

Slate is common on older roofs in the area, and some of those roofs are in conservation areas or on listed houses. The planning position is checked for the address, and it is worth checking before you choose a window.

A conservation rooflight is a slim-framed unit made to sit flush with the slate line, with a thin glazing bar and a single low profile. It is a different product from a standard roof window, and it often suits older roofs better. Our page on conservation rooflight installation covers the product and the approach. A standard window on a slate roof may need planning permission, or may not, depending on the property and the council. For general guidance you can read the national rules on the Planning Portal, and for a specific address we check at the survey.

Sound matters on slate too. A slate roof is a hard, thin covering. In the loft below, rain on it is audible, and a window can bring that closer to the bedroom. A laminated acoustic inner pane and well-seated seals are a sensible choice. We write what we chose into the quiet spec for the room, and our piece on acoustic glazing options for roof windows in loft bedrooms explains the build.

These come up at the survey when slates are visible from the ladder.

Will fitting a window crack my slates?

It should not. Slates are lifted by hand and stacked, and only the ones that must be cut are cut. A slate that is already cracked or loose at the edge of the opening is easier to spot when the work starts, and we replace it with a matching one.

Is the flashing different for slate?

Yes. The slate kit has a low profile to suit the flat covering, and the apron and side pieces are shaped accordingly. Using the wrong kit leaves gaps at the sides, so the kit is chosen for the covering, not for the window alone.

Does a slate roof cost more to fit?

It can, because of the careful lifting and cutting. The quote explains what is included, and general guides to roof glazing costs are on the costs page.

How do I arrange a survey?

Send photographs of the roof on WhatsApp, or use the quote page. The wider process is set out in our roof window installation guide.