Roof Repointing Guide: Ridge Tiles, Verges and Mortar

Three places, mainly. Along the ridge, bedding the ridge tiles onto the top of both slopes. Along the hips on a hipped roof, doing the same job on the diagonal. And at the verge, the gable edge, where the tiles overhang the wall and are bedded onto an undercloak.

Some older roofs also use mortar fillets where the roof meets a chimney or a wall. That was never a good detail and should be replaced with lead rather than repointed.

Valleys and abutments should be lead, not mortar. If you have cement in those places, repointing is not the answer, re-leading is.

From the ground, look along the ridge line against the sky. Gaps, missing sections and dark shadow lines between ridge tiles are visible from the pavement with binoculars.

Mortar debris in the gutters or on the ground after wind is the second sign. Sand-coloured crumbs at the base of a gable wall mean the verge is going.

A ridge tile that rocks when nudged is urgent. A loose ridge tile in a gale is a genuine danger to whatever is below it, and insurers take a dim view of damage caused by a defect you already knew about.

Mortar is rigid. The roof beneath it moves with temperature and with the building. Over years of expansion, contraction and wind loading, hairline cracks open in the bedding.

Then water gets in, freezes, and expands. Each frost widens the crack slightly. Twenty winters of that on an exposed North East ridge is enough to break the bond completely, which is why so many local roofs need ridge work at around the twenty to thirty year mark.

Poor original mixes accelerate it. Too much sand and the mortar is weak from day one. Too much cement and it is brittle and cracks early. Getting the mix right for the exposure is a craft skill, not a formula off a bag.

Traditional repointing strips the failed mortar, cleans the tiles, and re-beds them in fresh mortar to the correct mix. Done well it gives another twenty years or so and keeps the traditional appearance, which matters on period and conservation properties.

Dry fix does away with mortar altogether. Ridge tiles are mechanically fixed with screws and clamps onto a ventilated ridge roll, and verges use a dry verge unit clipped over the tile edge. Nothing can crack out because nothing is bedded.

Dry fix costs slightly more up front and is effectively maintenance free for the life of the roof. It also adds high-level ventilation at the ridge, which helps the loft breathe. On any full re-roof we specify dry fix as standard unless the property calls for traditional bedding.

The failed mortar has to come out properly, not be skimmed over. A thin new layer applied on top of old crumbling bedding has nothing to grip and will fail within a couple of winters. This is the most common corner cut in the trade.

Ridge tiles are lifted where the bedding beneath has gone, the surfaces are cleaned, and the tiles are re-bedded solid with the joints struck neatly. Verges are re-bedded onto a sound undercloak, replacing the undercloak where it has broken down.

The mortar is then protected while it cures. Repointing done in the rain or in a hard frost will not achieve strength, which is why we plan mortar work around the weather rather than the diary.

Ridge repointing on a typical house runs from around £500 to £1,200 depending on ridge length, access and whether hips are included. A gable verge is usually £300 to £800. Converting to dry ridge and dry verge typically adds a few hundred and removes the job permanently.

Access dominates the cost, as it does with all high-level work. If you are already having scaffolding up for a chimney, roofline or repair job, this is the moment to sort the pointing too.

If your ridge has visible gaps, do not wait for a leak. Water entering at the ridge runs a long way along the underlay before it appears inside, so by the time you see a stain the timber has usually been wet for a while.