Sitting flush with a thick clay pantile

Why it is difficult

On slate or plain tile, the covering is flat and a flush unit beds into it cleanly. The soakers lie against a flat surface and the geometry is simple.

On a pantile, every course presents a roll and a valley alternately. The soakers have to be dressed into that profile so water running down the roof is carried around the opening at every point, not just at the flat parts.

Getting it wrong leaves a route under the roll, and on an exposed Essex roof that is a leak within a season.

Cutting

Pantiles have to be cut to close against the unit, and a cut pantile loses the interlock that makes it weathertight. The cut edges have to be supported and lapped so they do not rely on that interlock.

Old clay pantiles are also brittle. Expect breakages when lifting, and expect to need replacements. On a roof of obsolete tiles, sourcing matching reclaimed ones is part of the job and it is worth establishing availability at survey rather than with the roof open.

Setting out

The unit has to align with the tile courses, not just with the room below. A conservation rooflight set half a course out is obvious from the lane, and on a roof that has moved over two centuries the courses are rarely regular.

That is why we set out from the roof rather than from a drawing.

Time

A flush unit in pantile takes meaningfully longer than the same unit in slate. It is worth paying for. A correctly bedded unit is nearly invisible from the road; a badly fitted one is the first thing you see.

What makes pantile difficult

Depth and irregularity.

A pantile has an S shaped profile: a roll on one side, a trough on the other, interlocking with its neighbour. That profile stands up substantially from the batten line, far more than a plain tile or a slate.

So the plane of the roof, as your eye reads it from the garden, is well above the plane the rooflight frame sits on. A unit that sits low relative to the timbers can still stand proud relative to what you actually see.

And clay pantiles, particularly old hand made ones, are irregular. They vary in camber, in thickness and in colour, and no two courses lie in quite the same plane. A flashing has to accommodate that variation rather than assume a flat surface.

What flush means on this covering

Genuinely flush, as in the glass finishing level with the tile surface, is not achievable on a deep profile pantile and should not be promised.

What is achievable is a unit that sits as low as the profile allows, with the flashing dressed into the tile form well enough that the eye reads it as part of the roof rather than an object on top of it.

That is the honest target, and it is worth setting expectations at survey rather than after installation.

The flashing profile

This is where the job succeeds or fails.

Flashing kits come in profiles matched to the covering type, and there is a specific profile for deep tiles. It is not the same product as the one for slate or plain tile, and using the wrong one is the commonest fault on pantile installations.

A flat profile kit on a pantile roof cannot follow the tile form, so it bridges across the rolls and leaves voids in the troughs. Those voids are open channels straight under the flashing, and driven rain finds them.

The deep profile kit has a corrugated or formed apron designed to be dressed down into the troughs and over the rolls, so it follows the covering rather than sitting above it. Fitted correctly, there is no continuous void.

Where the tile is a hand made or unusual pantile that no standard kit suits, the answer is lead dressed on site by somebody who can do it. That is a leadworking skill, it takes time, and it should be priced honestly rather than substituted with a kit that nearly fits.

Cutting tiles around the opening

Pantiles interlock, so removing one is not like lifting a slate. The tiles around the opening have to be cut, and cut pantiles lose part of their interlock.

A cut edge that no longer engages with its neighbour needs mechanical fixing and needs to be supported by the flashing rather than relying on the interlock that has been removed.

Where cutting would leave a very narrow sliver of tile, the correct move is to widen the cut and use a wider piece, or to adjust the opening position by a small amount so the cuts fall in better places. That is a decision made on the roof with the covering off, and it is one of the reasons an experienced fitter produces a visibly better result on this covering.

The underlay collar

More important on pantile than on a flat covering, because the covering itself is less reliable at excluding driven rain.

A pantile roof relies on the underlay as a genuine secondary barrier. Water does get under pantiles in wind driven rain, runs down the membrane, and is discharged at the eaves.

So the collar around the rooflight opening has to be dressed and lapped so that water arriving on the membrane above the unit passes around it and continues down, rather than arriving at the opening and stopping.

Sequence: underlay collar first, lapped over the membrane below and under the membrane above, then the flashing, then the tiles reinstated over the flashing.

On an older pantile roof there may be no underlay at all. That is normal on a period building and it means the detail is built differently, around the opening rather than lapped into a membrane. It takes longer and it should be identified at survey rather than discovered on the day.

Which unit suits

On a pantile roof in a sensitive location, the low profile conservation rooflight is still the better looking answer, but the gain over a standard roof window is smaller than it is on slate. The tile profile is doing more to determine the visual result than the unit is.

Which means the cost benefit calculation shifts. On a slate roof, a conservation unit transforms the appearance. On a deep pantile it improves it, but the improvement is less dramatic, and a well fitted standard window with the correct deep profile flashing may be the better value on a rear slope.

Where consent is the driver rather than preference, ask the conservation officer directly what they will accept on this covering. Some are relaxed about pantile precisely because the profile limits what is achievable; others are not.

Colour matching

Old clay pantiles weather to a range of oranges, browns and blacks, frequently with lichen. A new tile alongside them is obvious.

Where tiles break during the work, and some will, the answer is not to buy new ones and put them beside the opening. It is to take sound tiles from a hidden slope or from the lowest course, use those around the rooflight where they will be looked at, and put the new tiles where they will not.

Reclaimed pantiles are widely available in this part of the country and are worth sourcing in advance on a roof of any age. A small stock of matching tiles on site avoids a compromise made under time pressure.

Pitch

Pantile roofs are often laid at moderate pitches, sometimes lower than a plain tile roof would allow, because the interlock and the profile let them get away with it.

A lower pitch means water moves more slowly and driven rain has more opportunity to get under the covering. Every detail around the rooflight has to be that much better as a result, and a shallow pantile roof is not a place to accept an approximate flashing job.

Check the manufacturer minimum pitch for the roof window itself as well. Standard roof windows have a minimum pitch below which they are not warranted, and some pantile roofs sit close to it.

Setting expectations at survey

Genuinely flush, with the glass level with the tile surface, is not achievable on a deep profile pantile and should not be promised.

What is achievable is a unit sitting as low as the profile allows, with the flashing dressed into the tile form well enough that the eye reads it as part of the roof rather than an object on it.

Saying that at survey rather than after installation is the difference between a satisfied customer and an argument, and any installer who promises flush on pantile is either inexperienced or telling you what you want to hear.

Where a pantile roof holds water

The troughs. Each trough is a channel running down the slope, and at the head of a rooflight those channels are interrupted by the flashing.

Water arriving in a trough has to be lifted over or diverted around the flashing, and if the flashing does not sit down into the trough properly, water runs under it instead.

That is the specific failure mode on this covering, and it is why the profile of the kit matters so much more here than on slate.

Hand made against machine made

Worth distinguishing, because they behave differently under the hands.

Machine made pantiles are dimensionally consistent, so a standard deep profile kit fits them predictably and cuts are repeatable.

Hand made pantiles vary in camber, thickness and length. No standard kit follows them exactly, and the answer on a roof of quality is lead dressed on site by somebody who can do it. That is a leadworking skill, it takes time, and it should be priced honestly rather than substituted with a kit that nearly fits.

Sourcing replacements before the day

Old clay pantiles are brittle and their nibs weaken, so a proportion will break on removal. Assume it rather than hoping.

Reclaimed pantiles are widely available in this part of the country and worth sourcing in advance, matched by colour and profile as closely as possible.

Where an exact match cannot be found, use the best matches around the rooflight where they will be looked at, and put anything that does not match on a hidden slope.

Minimum pitch

Pantile roofs are frequently laid at moderate pitches, sometimes lower than plain tile would allow, because the interlock and the profile permit it.

Check the manufacturer minimum pitch for the roof window itself as well as for the covering. Some pantile roofs sit close to it, and below it the unit is not warranted and a flat roof product on a kerb is the correct answer instead.