How long does a slate roof last?

Why the nails give up before the slate

Good natural slate is a dense, layered stone that sheds water and shrugs off frost. The parts around it are far less durable. Each slate hangs from one or two nails driven into a batten, the timber strip fixed across the rafters. On older roofs those nails were often iron, and iron rusts. When a nail corrodes through, the slate slides down out of its course. Roofers call this nail sickness, and across a whole roof it marks the end of the fixings rather than the slate. The Stirling City Heritage Trust describes exactly this: iron or poorly galvanised nails corrode, the slate slips, and the result is termed nail sickness.

The battens age too. Damp from condensation or a long-standing leak softens the timber, nails lose their grip, and the slope starts to look uneven. Below them, many older roofs have either no underlay or an early felt that has become brittle. Underlay is the sheet laid under the battens to catch water blown past the slates, and without it a single slipped slate lets rain straight onto the loft floor.

So a slate roof can often be reused. When the fixings fail, the slate comes off, is graded by hand, then goes back up over fresh battens with copper or stainless nails, with new slate making up any shortfall. You can read more about how we approach this on our slate roofing service page.

Welsh, Spanish and man-made slate

Slate is not one material. Its life depends on where it was quarried and how it was graded.

Welsh slate is what many older Bath houses carry. MyBuilder's 2026 guide has good Welsh slate commonly passing 100 years, and the Welsh Slate quarry claims over 100 years of useful life for its own stone. MyBuilder gives Spanish slate 75 to 100 years, and notes that even well-quarried slate nailed carelessly may give out in 10 years or less. Spanish slate is cut in a wide range of quarries and sold in several grades. The better grades make a long-lasting roof. Lower grades can contain iron minerals that rust and run down the slope as brown streaks, or can split into layers sooner than a denser stone would. When choosing Spanish slate, the quarry and the grade matter more than the country.

Man-made slate, made of fibre cement or a resin mix, is a different product. It is lighter and more uniform, and it is often chosen on cost. It generally wears out sooner than a good natural slate: MyBuilder gives fibre-cement and synthetic slate 30 to 50 years, and SSQ, a natural-slate supplier, says 30 to 40, and its edges and surface weather in a way stone does not, so the manufacturer's own guarantee and fixing instructions are the best guide to what you can expect. If the house is listed, or its roof is visible in a conservation area, ask B&NES planning before swapping natural slate for man-made.

Signs a slate roof is reaching the end

A slate roof seldom fails all at once. It sends warnings, and the pattern of them tells you whether the slate, the fixings or both have reached the end.

• Slipped slates on more than one slope. One slipped slate is a repair. Gaps appearing across the roof after every winter point to nail sickness everywhere.
• A roof dotted with tingles. A tingle is the small metal strap used to hold a replacement slate. A scattering of them shows years of patching.
• Flaking or soft slate. Slates that are splitting into layers, crumbling at the nail holes or turning powdery at the edges have reached the end of their own life, not just their fixings.
• Damp battens or daylight from the loft. Stains on the timber, rot at the batten ends or light through the slope mean water is getting past the slate.
• A sagging line. A ridge or slope that has dropped out of true can mean tired battens or a structural problem below them.

Any one of these alone may still be repairable. Several together usually mean patching has run its course. Our page on whether to repair or re-slate sets out how we make that call on a real roof.

What a re-slate keeps and what it replaces

A re-slate is not the same as throwing a roof away. When we strip a slate roof, every slate is checked as it comes off. Sound slates are stacked for reuse, usually on the slopes the street sees, while cracked, soft or flaking ones are discarded. New or reclaimed slate, matched for size and tone, makes up the shortfall.

Everything below the slate is renewed. New underlay goes on the rafters, new battens are fixed at the gauge the slate size needs, and the slates are nailed with copper or stainless nails that will not rust as the old iron ones did. Lead at the stack, walls and valleys is normally replaced at the same time, since reaching it later would mean lifting new slate.

The Planning Portal sets the line: re-covering escapes approval only where under 25 per cent of the total building envelope and under 50 per cent of the roof is affected. Stripping and re-slating a whole roof crosses both, so approval normally applies, and better loft or rafter insulation may be required. We deal with building control for you when it applies.

Cost depends on the slate, the size and shape of the roof, scaffold and how much of the old slate can be reused. For natural slate laid, MyBuilder's 2026 typical UK range is £100 to £180 per square metre. The slate roof cost guide unpicks those figures and what moves them, and your own fixed price is given in writing after the survey.

Making the slate roof you have last longer

The cheapest way to extend a slate roof's life is to deal with small faults before they let water reach the timber. A slipped slate replaced promptly protects the batten under it. A gap left through a wet winter can rot it.

Gutters matter more than people expect. When a gutter overflows, water runs back under the bottom course and soaks the eaves timbers, which are often the first to rot on an older roof. Clearing gutters and valleys of leaves and moss is simple work with a direct effect on the roof's life.

Lead is the other weak point. A flashing, the lead dressed over a joint where the roof meets a chimney or wall, can lift in wind or crack with age, and a small split lets water into the very place a roof is hardest to dry out. Having the lead looked at from time to time, and after any storm, costs far less than the damp it prevents.

Finally, keep pressure washers off slate. MyBuilder's roof cleaning guide warns the method can harm delicate tiles, and slate edges are no exception. Walking on slate cracks it too. After a hard winter, a look along the eaves and valleys from the garden, with binoculars if you have them, will show a slipped slate before the batten behind it starts to rot.