How do you match a rooflight to old handmade tiles?

What a handmade clay tile is, physically

A handmade plain tile is a slab of clay thrown into a sanded mould, struck off, turned out and dried before firing. Nominally around 265mm by 165mm, roughly 12mm to 15mm thick, hung on battens at a gauge of about 100mm so that every part of the roof is three tiles deep.

The important properties are the ones that come from being made by hand. It has a camber along its length, put there deliberately so the tail sits down onto the tile below and water cannot track sideways. It usually has a cross-camber as well, a slight twist across the width. The sanded face gives it texture and holds lichen. And the colour varies from tile to tile and from kiln to kiln, which is why an old roof reads as a field of related tones rather than a single flat colour.

None of those things is consistent. Two tiles from the same batch differ measurably in length, thickness and curve.

The camber is why a standard flashing struggles

A pressed flashing skirt is manufactured to bridge a known shape. On a flat slate it lies down. On a machine-made concrete tile it follows a roll that is identical every time.

On a handmade tile it has to sit across a curve whose height varies from tile to tile. Press a flat-covering skirt onto that and it bridges the high points and leaves a void at every camber, typically 5mm to 10mm of open gap running the length of the unit on both sides. That void is not a leak in still weather. In a driving south-westerly it is a direct path under the covering, and the mark that eventually appears inside is not below the rooflight but somewhere down the slope where the underlay first sags.

The flashing choice on a cambered tile

The proprietary answer is a profiled flashing kit, sold for tiles with a profile up to about 120mm, dressed down hard onto the camber by hand once it is in position. On a regular handmade tile with a consistent camber that works, and it works well, provided the fitter actually dresses it rather than laying it on.

Where the tiles are older, more irregular or a mix of salvaged stock from more than one source, the honest answer is lead. Individual soakers are cut and set into the courses at each side, and the apron is bossed to follow the tiles actually beneath it rather than a nominal profile. That is slower and it is skill rather than product, and it is the first thing thinned out when a roof has been priced as though it were modern.

Either way, the head flashing is set under a full course and the underlay collar goes in behind it. Those parts do not change with the covering, and they are covered in more depth on what is a conservation rooflight flashing kit?

Tiles come off in order and go back on

The best matching tiles on the market are already on your roof. They have weathered under the same sky for a century, they carry the same lichen, and they came from the same kiln.

So the tiles lifted to form the opening are handled as material, not waste. They come off in course order, stacked on edge in the order they were lifted, kept off the ground and kept out of the way of anyone walking. Handmade tiles are brittle at the nib and a stack knocked over loses a good proportion of it. Peg holes and nibs are checked as they come off, because a tile with a broken nib can still be used lower down where it is nailed rather than hung.

Around the finished unit, those same tiles go back. The cut pieces that inevitably fall at the flashing line are made from the poorest of the salvaged stock, not the best, and the best go where they are visible.

Where replacements come from when tiles break

Some always break. Nibs go, tails snap, and tiles that have been mortar-torched from below sometimes come off in two pieces. So a proportion of extra stock is needed, and it comes from reclaim rather than a builders’ merchant.

Sorting is the part people underestimate. A reclaimed handmade tile of roughly the right colour is not automatically the right tile. It has to be within the size band of the tiles around it, within a few millimetres of the same thickness, and carrying a camber of similar depth, or it will sit proud and cast a shadow line that is visible from the road. New handmade tiles are still made in this country and they are excellent, but next to a century-old roof they read as new, and they go on reading as new for a very long time.

Where a roof is stone rather than clay, the sourcing question is different again and covered on can you fit a rooflight in a stone slate roof?

Setting out to the gauge so nothing has to be cut

At a 100mm gauge you have a fine-grained roof, which is an advantage. The head and foot of the unit can nearly always be landed on a course line, so the flashing finishes under whole tiles above and discharges onto whole tiles below, with no row of cut pieces at either end.

That is set out on the roof before anything is lifted. We measure the actual gauge over ten courses rather than assuming 100mm, because an old roof drifts, and the drift accumulates. Then the frame height is chosen and the position adjusted up or down by a course to land it cleanly. Moving a unit 40mm to avoid a row of cut tiles costs nothing at that stage and cannot be done at all afterwards.

Frame finish, and why flush counts double here

An old clay roof has almost no flat surfaces on it. Everything is slightly curved, slightly uneven, and the whole plane has a texture that catches light. Drop a projecting aluminium box onto that and the contrast is not the colour, it is the flatness and the shadow it casts.

A recessed conservation unit in a dark finish, set so the glass comes down close to the plane of the tiles, avoids nearly all of that. The glass takes the sky, which on most days is a similar tone to a weathered clay roof, and there is no shadow line under a raised frame. We install VELUX, Fakro, Keylite and Roto units including their conservation ranges, and on handmade tile we would recommend one every time, whether or not the building is designated.

A glazing bar down the centre helps as well on a larger unit, because it breaks the reflection into two panes at the scale of the surrounding tile work rather than one large mirror.

Peg-hung, nib-hung and torched roofs

What is holding the tiles on changes how the roof comes apart. Nib-hung tiles lift off a batten cleanly. Peg-hung tiles, common on the oldest roofs around the county, hang on oak or bone pegs through two holes, and every peg found intact is a tile that will hang again.

Torched roofs, where lime mortar was pointed to the underside of the tiles from within the loft, are the slowest. The torching has to be broken back carefully around the opening or it drops in sheets, and where the roof has no underlay at all, one goes in locally around the unit as part of the work along with the collar. Those conditions are found rather than assumed, and they are the reason we look inside the roof at the survey as well as on top of it.

How a day on a handmade tile roof runs

Scaffold or a tower goes up first, because tiles this fragile are not thrown down and nobody works off a ladder over them. The set-out is marked on the roof and agreed. Then the tiles come off in order and are stacked, the battens are cut back, the trimming is formed, the collar and unit go in, the flashing is fitted and dressed, and the tiles go back around it.

The roof is never left open overnight. If the weather or the structure means the work will not close in the same day, the opening is boarded and covered before anyone leaves, and we would rather move the date than start a job we cannot close.

Four details decide whether it stays dry: the collar behind the head, the gutter above the frame, the lap of the soakers into the courses, and where the tiles terminate against the flashing. All four disappear the moment the covering goes back, which is why the workmanship carries a ten-year guarantee. Fifteen years of these roofs, a range by email once we know what the covering is, and a fixed price after the survey.