Is mortar bedding still allowed for ridge tiles?

1What the standard changed

BS 5534 covers how slate and tile roofs are laid and fixed. BSI lists the current version as BS 5534:2014+A2:2018, published in February 2018, and designers, roofers and manufacturers all work from it when they decide how a roof should be held down.

Marley describes the shift in a few lines. Until the 2014 revision, a mortar bed with nothing else behind it was still commonly accepted on ridges. After it, the pull-off strength of mortar could not be counted on to keep a ridge or hip tile in place, and bedded fittings should have mechanical fixings. People read that as a ban, but the word that matters is partner. Mortar has not been taken off the roof. It has been given a second fixing to work alongside.

2Law, contracts and common sense

Marley is clear on one point that surprises many homeowners: working to BS 5534 is not required by law. Nobody will fine you for an older mortar ridge. The standard bites when it is written into a contract, a specification or a manufacturer's warranty, and a roofer who knows it will normally follow it in any case.

The practical argument is stronger than the legal one. A ridge is the highest part of the roof and takes the wind first. Marley adds that edge tiles were to be fixed twice, and that ridge, hip and single-lap tiles all needed a mechanical fixing whatever the mortar was doing. That is the sensible line to hold. When you ask for a quote, ask what the ridge will be fixed with as well as what it will be bedded in. The page on gaps under the ridge tiles shows what happens when a bed is the only thing in charge.

One more caution. The 2018 amendment recognises that the standard may not suit every heritage roof, and the advice is to involve the council and a conservation specialist.

3What a sound mortar ridge looks like now

From the street, a modern bedded ridge looks just like an old one. The difference is out of sight. The tiles are held back to the roof structure by clips or screws, and the mortar only seals the joint, evens out the bed and keeps the line neat. If the bed cracks in a few winters, the ridge is still held and the repair is a re-point.

A ridge laid the old way depends entirely on the mortar staying stuck to both tiles. Salt air, frost and a long run of gales slowly break that bond. The ridge starts to rock, a gap opens, and the next storm finds it. There is rarely a warning from the ground until the tile moves.

If you are weighing up the two approaches side by side, our guide to mortar versus dry fix compares them, and the page on the mortar mix for ridge tiles covers the material itself.

4Questions to put to a roofer about a mortar ridge

If you are getting a quote for a ridge, a few plain questions tell you a great deal. What is each tile fixed to, apart from the bed? What happens to the old mortar? Is the ridge board checked for rot before the tiles go back? Will the colour of the mortar match the tile? And if the weather turns, how is the open stretch protected?

A roofer who answers in detail has done the job before. One who says the mortar is enough on its own is describing the way ridges were done before the standard changed. You can also ask to see photographs of the bed before and after, which is how we work: the survey images come with the written quote, which lets you compare the state of the bed before and after.

5Mortar or a dry-fix system: which suits your roof

Either route can meet the standard. A dry system replaces the bed with clips, screws and a flexible seal, and BS 8612:2018 is the test standard for such systems. Our page on the dry hip system explains the parts.

Mortar still makes sense where the roof is old and the appearance matters, where lime is the correct material, or where the existing bed is sound and a repair is all it needs. A dry system tends to suit a roof whose bed has failed repeatedly, a long run that would eat a lot of mortar, or an exposed edge where you want the tiles held by something that does not weather.

We trace the fault first, photograph your ridge, and recommend the lightest job that truly cures it. Where a re-point is enough, that is the job. Where the ridge must come off and be re-fixed, the photographs show why. The wider service sits on the ridge tile repairs page.