Question 1

Why do ridge tiles come loose?

Accepted Answer

Because on most older roofs they are held on by mortar alone, and mortar on the most exposed line of the building cracks through freeze-thaw and thermal movement. Since BS 5534 was revised in 2014, mortar on its own is no longer an accepted fixing — ridges, hips and verges must all be mechanically fixed as well. The ridge is the highest and most exposed line on the roof. It takes weather from both sides, has nothing above it, and until relatively recently it was held on by nothing but a bed of sand-and-cement mortar. That mortar takes the full force of frost, heat and wind pressure, and eventually it cracks. Once it has cracked, two things follow. Water gets into the crack and into the roof space, and the bond holding a heavy tile at the top of the building starts to go. A ridge tile coming off is a leak and a falling-object risk, and where there is a footpath or a drive underneath, the second is the more serious. Freeze-thaw is the main driver, and that is why it happens faster in some parts of this patch than others. Temperature falls roughly half a degree per hundred metres, and the Met Office records substantially more air frost on the high ground than on the Cheshire plain — Buxton averages 51.5 air-frost days a year against 40.0 at low-lying Woodford. Kerridge Hill is 313 metres. A ridge up there gets many more freeze-thaw cycles a year than the same ridge in the town centre, and it fails correspondingly sooner. The mortar mix itself decides a lot. Too rich a mix — too much cement — shrinks as it cures and cracks early, and it is harder than the tile it is bedded against. A properly graded mortar laid in decent conditions and protected while it cures lasts far longer. Ridge work done in frost, or in baking sun with no protection, is compromised before it has set. The standard changed for exactly this reason. BS 5534, the code of practice for slating and tiling, was substantially revised in 2014, and mortar is no longer accepted as the sole fixing for ridges, hips or verges. Every unit now has to be mechanically fixed as well — either through a dry-fix system with a ventilated ridge roll and screwed units, or with clips and screws set under a traditional mortar bed where the appearance matters. That means a quote to simply re-bed a ridge in mortar is a quote to a superseded standard. On an exposed roof it is a quote to do the job again after the next serious gale. If somebody offers to re-bed your ridge, ask what mechanical fixing is included.

Question 2

Why did my ridge tile fall off?

Accepted Answer

Because on most older roofs they are held on by mortar alone, and mortar on the most exposed line of the building cracks through freeze-thaw and thermal movement. Since BS 5534 was revised in 2014, mortar on its own is no longer an accepted fixing — ridges, hips and verges must all be mechanically fixed as well. The ridge is the highest and most exposed line on the roof. It takes weather from both sides, has nothing above it, and until relatively recently it was held on by nothing but a bed of sand-and-cement mortar. That mortar takes the full force of frost, heat and wind pressure, and eventually it cracks. Once it has cracked, two things follow. Water gets into the crack and into the roof space, and the bond holding a heavy tile at the top of the building starts to go. A ridge tile coming off is a leak and a falling-object risk, and where there is a footpath or a drive underneath, the second is the more serious. Freeze-thaw is the main driver, and that is why it happens faster in some parts of this patch than others. Temperature falls roughly half a degree per hundred metres, and the Met Office records substantially more air frost on the high ground than on the Cheshire plain — Buxton averages 51.5 air-frost days a year against 40.0 at low-lying Woodford. Kerridge Hill is 313 metres. A ridge up there gets many more freeze-thaw cycles a year than the same ridge in the town centre, and it fails correspondingly sooner. The mortar mix itself decides a lot. Too rich a mix — too much cement — shrinks as it cures and cracks early, and it is harder than the tile it is bedded against. A properly graded mortar laid in decent conditions and protected while it cures lasts far longer. Ridge work done in frost, or in baking sun with no protection, is compromised before it has set. The standard changed for exactly this reason. BS 5534, the code of practice for slating and tiling, was substantially revised in 2014, and mortar is no longer accepted as the sole fixing for ridges, hips or verges. Every unit now has to be mechanically fixed as well — either through a dry-fix system with a ventilated ridge roll and screwed units, or with clips and screws set under a traditional mortar bed where the appearance matters. That means a quote to simply re-bed a ridge in mortar is a quote to a superseded standard. On an exposed roof it is a quote to do the job again after the next serious gale. If somebody offers to re-bed your ridge, ask what mechanical fixing is included.

Question 3

Ridge tiles keep coming off — why?

Accepted Answer

Because on most older roofs they are held on by mortar alone, and mortar on the most exposed line of the building cracks through freeze-thaw and thermal movement. Since BS 5534 was revised in 2014, mortar on its own is no longer an accepted fixing — ridges, hips and verges must all be mechanically fixed as well. The ridge is the highest and most exposed line on the roof. It takes weather from both sides, has nothing above it, and until relatively recently it was held on by nothing but a bed of sand-and-cement mortar. That mortar takes the full force of frost, heat and wind pressure, and eventually it cracks. Once it has cracked, two things follow. Water gets into the crack and into the roof space, and the bond holding a heavy tile at the top of the building starts to go. A ridge tile coming off is a leak and a falling-object risk, and where there is a footpath or a drive underneath, the second is the more serious. Freeze-thaw is the main driver, and that is why it happens faster in some parts of this patch than others. Temperature falls roughly half a degree per hundred metres, and the Met Office records substantially more air frost on the high ground than on the Cheshire plain — Buxton averages 51.5 air-frost days a year against 40.0 at low-lying Woodford. Kerridge Hill is 313 metres. A ridge up there gets many more freeze-thaw cycles a year than the same ridge in the town centre, and it fails correspondingly sooner. The mortar mix itself decides a lot. Too rich a mix — too much cement — shrinks as it cures and cracks early, and it is harder than the tile it is bedded against. A properly graded mortar laid in decent conditions and protected while it cures lasts far longer. Ridge work done in frost, or in baking sun with no protection, is compromised before it has set. The standard changed for exactly this reason. BS 5534, the code of practice for slating and tiling, was substantially revised in 2014, and mortar is no longer accepted as the sole fixing for ridges, hips or verges. Every unit now has to be mechanically fixed as well — either through a dry-fix system with a ventilated ridge roll and screwed units, or with clips and screws set under a traditional mortar bed where the appearance matters. That means a quote to simply re-bed a ridge in mortar is a quote to a superseded standard. On an exposed roof it is a quote to do the job again after the next serious gale. If somebody offers to re-bed your ridge, ask what mechanical fixing is included.

Why do ridge tiles come loose?

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