Question 1

How long does a slate roof last?

Accepted Answer

The slate itself will do a century and often considerably more — it does not absorb water and it does not degrade in frost. What ends a slate roof is the fixings: original iron nails typically start failing somewhere between eighty and a hundred and twenty years, which is why so many roofs in this town are being stripped and re-laid now. Slate is a remarkable roofing material and the reason so much of Macclesfield's older housing still has its original covering. It is effectively impermeable, dimensionally stable, and unaffected by frost. Failures in a hundred-year-old slate roof are almost never the slate. They are the nails. Victorian and Edwardian roofs were fixed with iron nails, and iron in a roof space corrodes. After a century or so the nails no longer hold the weight of a slate, and they fail one at a time, over years, in no particular order. That is nail sickness, and it is the single commonest reason an old slate roof comes off. The pattern is what identifies it: slates slipping two or three a year from different slopes, rust-coloured staining running down below the nail positions, and reddish grit in the gutters. From inside the loft the nail heads are visibly swollen and rusted, and slates that should be solid move under a gentle push. The good news is that a strip and re-lay is much less wasteful than it sounds. On a typical hundred-year-old Welsh slate roof a large majority of the slates come off perfectly sound and go straight back on, with reclaimed matching stock making up the shortfall. Re-laid on new treated battens with copper or stainless nails and a breathable membrane, the same slates should comfortably see out another lifetime. Local context matters here. VOA council tax data puts central Macclesfield at 54.1% pre-1919 against an England average of 20.1%, so the town centre has an unusual concentration of roofs at exactly this age. Tytherington, by contrast, is 1.5% pre-1919. Two roofs a mile and a half apart in this town can be at completely different points in their lives. One caveat worth knowing: not all slate is equal. Good Welsh slate is the benchmark. Some cheaper imported slate has performed poorly, delaminating or discolouring within a couple of decades. If a roof was re-covered in the last thirty years and the slates are already flaking, that is a material problem rather than a fixings one.

Question 2

Life expectancy of a slate roof

Accepted Answer

The slate itself will do a century and often considerably more — it does not absorb water and it does not degrade in frost. What ends a slate roof is the fixings: original iron nails typically start failing somewhere between eighty and a hundred and twenty years, which is why so many roofs in this town are being stripped and re-laid now. Slate is a remarkable roofing material and the reason so much of Macclesfield's older housing still has its original covering. It is effectively impermeable, dimensionally stable, and unaffected by frost. Failures in a hundred-year-old slate roof are almost never the slate. They are the nails. Victorian and Edwardian roofs were fixed with iron nails, and iron in a roof space corrodes. After a century or so the nails no longer hold the weight of a slate, and they fail one at a time, over years, in no particular order. That is nail sickness, and it is the single commonest reason an old slate roof comes off. The pattern is what identifies it: slates slipping two or three a year from different slopes, rust-coloured staining running down below the nail positions, and reddish grit in the gutters. From inside the loft the nail heads are visibly swollen and rusted, and slates that should be solid move under a gentle push. The good news is that a strip and re-lay is much less wasteful than it sounds. On a typical hundred-year-old Welsh slate roof a large majority of the slates come off perfectly sound and go straight back on, with reclaimed matching stock making up the shortfall. Re-laid on new treated battens with copper or stainless nails and a breathable membrane, the same slates should comfortably see out another lifetime. Local context matters here. VOA council tax data puts central Macclesfield at 54.1% pre-1919 against an England average of 20.1%, so the town centre has an unusual concentration of roofs at exactly this age. Tytherington, by contrast, is 1.5% pre-1919. Two roofs a mile and a half apart in this town can be at completely different points in their lives. One caveat worth knowing: not all slate is equal. Good Welsh slate is the benchmark. Some cheaper imported slate has performed poorly, delaminating or discolouring within a couple of decades. If a roof was re-covered in the last thirty years and the slates are already flaking, that is a material problem rather than a fixings one.

Question 3

How old can a Welsh slate roof get?

Accepted Answer

The slate itself will do a century and often considerably more — it does not absorb water and it does not degrade in frost. What ends a slate roof is the fixings: original iron nails typically start failing somewhere between eighty and a hundred and twenty years, which is why so many roofs in this town are being stripped and re-laid now. Slate is a remarkable roofing material and the reason so much of Macclesfield's older housing still has its original covering. It is effectively impermeable, dimensionally stable, and unaffected by frost. Failures in a hundred-year-old slate roof are almost never the slate. They are the nails. Victorian and Edwardian roofs were fixed with iron nails, and iron in a roof space corrodes. After a century or so the nails no longer hold the weight of a slate, and they fail one at a time, over years, in no particular order. That is nail sickness, and it is the single commonest reason an old slate roof comes off. The pattern is what identifies it: slates slipping two or three a year from different slopes, rust-coloured staining running down below the nail positions, and reddish grit in the gutters. From inside the loft the nail heads are visibly swollen and rusted, and slates that should be solid move under a gentle push. The good news is that a strip and re-lay is much less wasteful than it sounds. On a typical hundred-year-old Welsh slate roof a large majority of the slates come off perfectly sound and go straight back on, with reclaimed matching stock making up the shortfall. Re-laid on new treated battens with copper or stainless nails and a breathable membrane, the same slates should comfortably see out another lifetime. Local context matters here. VOA council tax data puts central Macclesfield at 54.1% pre-1919 against an England average of 20.1%, so the town centre has an unusual concentration of roofs at exactly this age. Tytherington, by contrast, is 1.5% pre-1919. Two roofs a mile and a half apart in this town can be at completely different points in their lives. One caveat worth knowing: not all slate is equal. Good Welsh slate is the benchmark. Some cheaper imported slate has performed poorly, delaminating or discolouring within a couple of decades. If a roof was re-covered in the last thirty years and the slates are already flaking, that is a material problem rather than a fixings one.

How long does a slate roof last?

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