Rooflights in plain clay tile roofs

Why they are forgiving

Flat, like slate, so a flat profile flashing kit sits tight and a flush conservation unit beds in cleanly.

Being small, they also allow the opening to be set out more freely: with a large interlocking tile the opening tends to align to the tile module, whereas plain tiles give finer increments.

The volume of cutting

The trade-off. A plain tile roof has many more tiles per square metre, so an opening means cutting a great many of them, and each cut tile has to be supported and lapped so it does not rely on the interlock it has lost.

That is time rather than difficulty, and it is why a plain tile roof takes a little longer than slate.

Brittleness

Old clay plain tiles are fragile, particularly at the nibs, and breakages are normal when lifting. Expect to need replacements.

Matching matters: new clay beside hand made weathered clay is obvious. Reclaimed tiles of the right size and camber are worth sourcing, and availability is checked at survey rather than with the roof open.

Camber

Traditional plain tiles have a slight curve across their width, which is what keeps them shedding water. It also means the covering surface is not perfectly flat, and a flush unit is bedded with that in mind.

Conservation

Plain tile is the classic conservation rooflight context. A flush unit in plain clay tile, correctly set out to the courses, is nearly invisible from the ground, which is exactly what makes an application succeed.

The most demanding covering in this trade

Plain clay tiles are small, laid in double lap so every point on the roof has two thicknesses of tile over it, and on older buildings they are handmade and irregular. They are also brittle.

None of that prevents a rooflight. It means the work is slower, more careful, and priced differently from the same job on a concrete tile roof.

What actually happens

Tiles have to be lifted individually over an area larger than the opening, because the double lap means you cannot simply remove a rectangle. Nibs and pegs have to be released without cracking the tile, and old clay does not always cooperate.

A proportion breaks whatever care is taken. That is not a sign of carelessness; it is the nature of a fifty or hundred year old handmade tile.

Matching

The real difficulty. Handmade clay varies in colour, texture and camber, and a weathered tile has a patina that a new one does not. Modern machine made plain tiles look wrong next to old handmade ones even where the dimensions match.

The usual answer is to take sound tiles from a rear or hidden slope, use those around the new opening, and put the replacements where they cannot be seen. On a listed building that approach may itself need describing in the consent application.

Where a reclaimed match can be sourced, it is worth the cost and the wait.

The flashing

Plain tiles need their own detail, generally using soakers interleaved with the tile courses rather than a single formed apron. It is more work than a proprietary kit on an interlocking tile and it is what makes the installation weathertight.

A universal flashing bodged onto a plain tile roof does not work, and it looks wrong from the ground as well.

What is underneath

On a roof that has never been stripped, frequently no underlay at all: tiles hung on riven battens with the rafters visible from inside.

Modern rooflight weathering assumes a membrane to lap into. Where there is none, the detail is built around the opening instead. That is normal on a period property, it takes longer, and it belongs in the quotation rather than in a conversation on the day.

Steep pitches, which help

Plain tile roofs are usually pitched at 40 degrees or more, because the covering needs it. That is good news for a rooflight: water sheds fast, gravity does much of the weathering work, and the headroom gain from a roof window is generous.

What to expect on a quotation

More time than the same job on concrete tile, an allowance for broken tiles, a stated approach to matching, and a contingency for decayed timber, which on a roof of this age is a realistic possibility rather than a remote one.

Why it is a favourable covering

Plain clay tiles are small, flat and laid in fine courses with a double lap. They lie close to the batten line, so a low profile unit reads as genuinely low rather than merely low relative to the timbers.

That makes plain tile, along with slate, one of the two coverings where a conservation rooflight looks its best and where a flat profile flashing lies tight with no voids beneath it.

The fine coursing also means cuts around the opening fall in manageable places rather than leaving awkward slivers.

Flashing into plain tile

A flat profile kit, matched to the window size. Soakers interleave with the courses up each side, an apron at the sill, a head flashing at the top with the tiles above lapping over it.

Underlay collar first, dressed and lapped, then the flashing, then the tiles reinstated over it.

Matching, which is the practical challenge

Old plain clay tiles weather to a range of oranges, browns and reds, frequently with lichen and moss. New tiles beside them are unmistakable.

Some will break during the work, particularly on a roof of age where the tiles have become brittle or the nibs have weakened. Allow for it.

The answer where an exact match cannot be found is to take sound tiles from a hidden slope for use around the rooflight and put the new ones where they will not be looked at. Reclaimed plain tiles are widely available in this part of the country and worth sourcing in advance.

What lies below the tiles

On an unstripped period roof, frequently no underlay at all, and sometimes torching: mortar applied to the underside of the tiles between battens as an early weather barrier. Both are normal, both take more time, and both should be identified at survey.