How long do fibre cement slates last?

Natural slate and concrete tile come with published expectations. CORC gives maintained slate 100+ years, and Marley reckons on around 60 years for concrete, adding that it is no guarantee. For fibre cement we have no equivalent figure to quote, and an invented one would mislead you. Different makers have used different formulations over the decades, and the oldest roofs on the street are not a fair guide to today's products.

What decides the life of a particular roof is a set of ordinary things: how dense the slate is, how well it was nailed, how steep the roof is, how much moss and debris it carries, and whether anyone has trodden on it. Two neighbouring houses fitted in the same year can age at different rates. Our page on natural against artificial slate compares the families of product. A maker's warranty, meanwhile, is a commercial promise about defects, and it tells you little about the working life ahead.

These slates age from the surface and the edges inward. Early on you see a darker, more uneven colour, with moss and algae collecting on the lower slopes. Later the surface roughens and fine hairline cracks appear. The corners and bottom edges chip, and slates start to break when someone steps on the roof or leans a ladder against it.

The worst sign is brittleness. A slate that snaps when a neighbour is lifted for a repair means the whole slope is likely to behave the same way, and every repair will cost more slates than it saves. Fixings matter too: if nails have rusted or heads have pulled through, the slates drop in groups. From the ground, look for a patchwork of colours, lines of broken edges and sagging courses. Natural stone fails differently, by shedding layers, as we describe on the delaminating slates page.

This is the part of the answer that matters most for safety. Where the house dates from before 2000, or was refurbished then, the HSE tells owners to presume asbestos is somewhere in it, and some artificial slates of that era may be asbestos cement. HSE classes asbestos cement roofing as non-licensed work when it is lifted carefully and not broken. Once it is badly damaged or broken up, the job becomes notifiable, and notice goes in before work starts.

HSE also calls asbestos cement roofing always fragile. For an owner, that comes down to three rules. Do not walk on the roof, pressure wash it, scrape the moss, or drill it. Do not hand a sample to anyone who has not been told what it may be. Fixings, flashings and ridge pieces on such a roof should be treated with the same suspicion as the slates themselves. And have the slates identified before any work is priced. Asbestos waste is wrapped twice, labelled and never mixed in with other rubbish, and the contractor fills in the consignment note as waste producer. Looks prove nothing here, so a roof is treated as suspect until it has been identified.

If a fibre cement roof is sound but has a few broken slates, a repair is reasonable, though an older roof still carries the asbestos caution above. Replacement slates should match in size and thickness, and a roofer should check the neighbours for movement before and after. If breakages are frequent, or the slates have gone brittle, each repair buys little, and renewing the covering is the more sensible course.

Re-roofing triggers questions about regulations, because a new covering of different weight needs checking. The Planning Portal sets the weight trigger for approval at a new covering 15 per cent heavier or more, and building control can confirm whether your job crosses it. Our slate roofing page sets out the replacement options, from new natural slate to modern artificial products, and the survey tells you which is realistic for your house. Whichever way it goes, the timber under the covering is looked at as well: battens that have been damp for years may need renewing, and that is easier to price before the roof is opened than after.

If you are buying a house, or just wondering what you have, start with the paperwork: a survey report, an energy performance certificate or old invoices may say what the roof was built from and when it was last touched. From outside, check the dates of the house, the colour pattern, and whether the roof looks identical across all slopes, which hints at a single original covering.

A roofer can then inspect it safely, photograph every slope and give you a clear call between a repair, a stopgap and a replacement. That verdict comes with the evidence, so you can decide at your own pace. Where the roof is heading towards replacement, plan for it rather than waiting for a gale to make the decision, because a planned job on a dry day costs less stress and usually less money than an emergency one.