How Long Should a Roof Last Before Replacement?

Most pitched roofs around Taunton are covered in one of three materials, and the published lives for them are the longest of any covering.

What life can you expect from slate?

CORC, the Confederation of Roofing Contractors, puts slate that is well maintained at 100+ years. The condition attached to that figure does real work. The stone itself is hard and slow to wear, but the nails holding it can rust and the battens behind it can rot, so a slate roof tends to be repaired many times before the slate is spent. On a Taunton terrace with a hundred-year-old roof, the question is nearly always about the fixings, not the stone. Our page on slate roof lifespan goes into that in more detail.

How do clay tiles compare?

Marley cites the BRE as giving clay a minimum life expectancy of 60 years, and that minimum is for clay only. A building-conservation article on old peg tiles cautions that 60 years can mislead for those, since their lives vary so widely.

What about concrete tiles?

Marley expects around 60 years from its concrete tiles and is explicit that the figure is neither a guarantee nor a warranty. It is a description of the product, not a commitment about your roof.

So these are not one figure under three labels. They come from different sources, measure different things and carry different cautions. A page that merges them into a single line saying tiles last 60 years has smoothed over the detail, and the detail decides whether your roof can be left alone or needs attention in the next few winters.

Flat roofs are covered in membranes, sheets that are bonded or fixed to a deck, and their published lives are shorter than for slate. They also vary more with the material and the standard of installation.

• Torch-on felt: Less gives 10 to 20 years, with the caution that workmanship decides whether a roof reaches the top of that range or fails early.
• GRP, glass-reinforced plastic laid as a jointless fibreglass skin: Less gives 25 to 40 years.
• EPDM, a single-piece rubber membrane stretched over the deck: GreenSpec gives an expected service life of 20 to 30 years, and Less says 30 to 50.

Why do the figures for EPDM disagree?

Because they come from different authors with different assumptions. GreenSpec is a building-product guide, and Less is a home-improvement site. Neither is wrong, and the gap is itself informative, because it tells you the real figure depends on the installer, the deck, the drainage and the exposure. When you hear one number quoted for EPDM, ask where it came from.

The point about workmanship in the felt range applies to every flat roof. A badly detailed upstand, the short upturn where the membrane meets a wall, or a low spot that holds water, will shorten a life more than the choice of membrane does. Our warm roof versus cold roof page covers how the build-up beneath the membrane affects it.

Garage roofs, porch roofs and extension roofs tend to be flat, so this section is relevant to many pitched-roof houses as well. Dormer cheeks and bay roofs can be covered the same way, and they often fail first because they sit where water collects.

A roof is more than its main covering, and some of its parts are meant to outlast it. Lead flashing and lead valleys are the obvious case. MyJobQuote says lead can last for over 80 years, and that is worth reading as a lower bound, not an average. Zinc has a longer published figure again: VM Zinc cites the BRE Environmental Product Declaration, which states 100 years.

Other parts do not match that. Ridge tiles bedded in mortar can fail while the tiles on either side are sound. A valley lined with an old bitumen product will age faster than the slate beside it. Plastic fascia, the board under the eaves that carries the gutter, has a retailer's figure of between 20 and 40 years, and a retailer has a stake in the answer, so weigh that figure accordingly.

Should I replace everything at the same time?

Not necessarily. When a roof is stripped for a new covering, the old lead, ridge and underlay are often renewed as a matter of course, since access is already there and the new covering has a long life ahead of it. Laying a new slate or tile covering around a lead valley with twenty years left is more of a judgement call, and the answer depends on how the lead looks once it is uncovered. We tell you what we find, with pictures, before the plan is settled.

Chimney flashings and flaunching, the mortar bed the chimney pot sits in, are the other details that age faster than the roof around them, and they are worth including in any assessment of the whole roof.

This is the most common mix-up in roofing. A warranty is a firm's written undertaking to repair certain faults within a stated period, subject to conditions. A lifespan is a forecast for the material itself, and nobody is committed to it. The two are separate, and a short warranty says nothing about a short life, just as a long one does not promise a long life.

Marley makes the point directly for concrete tiles. Around 60 years is expected of them, and the same page adds that this is no promise of longevity. The life expectancy describes the material. A warranty, if there is one, describes a contract.

Why does the distinction matter when you choose a roofer?

Because a quoted year count can mislead. A roof warranty may cover workmanship only, may exclude certain defects, or may rely on the company still trading when you need it. Ask what is covered, what is excluded, who stands behind it and what you must do to keep it valid, and ask for the answer in writing.

New-home cover works the same way. Under NHBC Buildmark the builder stands behind the home for the first 2 years, and years 3 to 10 are covered by NHBC insurance against defects in certain parts of the building. That is defect cover in two stages. It is not a forecast of how long the roof will last. Our guide to spotting a dodgy roofer covers what to ask any roofer to put in writing.

The takeaway is simple: use published lives to judge when to start paying attention, and use paperwork to judge who is accountable if something goes wrong. Keep the quote, the invoice and any certificate together in one folder, because they are what you will reach for in ten years.

A roof's age tells you where it sits in a published range. Its condition tells you what to do. Two roofs of the same age can be in very different states, and a younger roof with a fault can be in worse shape than an older one that has been looked after.

What should you look for?

• Slipped, cracked or missing slates or tiles spread over several spots, not a lone casualty.
• Rows that sag or ripple where the lines ought to be dead straight, which can mean the battens behind are failing.
• Daylight in the loft, or staining and damp patches on the timbers.
• Moss and growth that holds water against the covering.
• Lifting flashing and crumbling mortar at the ridge and chimney.

From the ground you can see the first two and the last, and from the loft with a torch you can see the rest. Our guide to checking a roof from the loft shows how. What the ground cannot show is the underside of a slate, the condition of a nail or the state of the underlay, which is why a roofer goes up.

One more point. When you are weighing a repair against replacement, age matters less than how widespread the faults are, and how far the damage reaches below the covering. A scattering of repairs on a sound roof is often the better buy, and that is the advice you get when the survey finds it.

Put the published lives together with the signs, and a decision begins to take shape. A slate roof of a hundred years with a few slipped slates is a repair. A concrete tile roof past sixty, with failing battens and spreading moss, is a different conversation. A felt flat roof at fifteen years with water ponding on it has probably reached the end of its working life. In every case the published figure frames the conversation, and the survey settles it.

When does replacing beat repairing?

When the covering, or the timber that carries it, is failing across a whole slope, so that each repair disturbs sound neighbours and the repairs keep coming. You are then paying again and again for patches on a roof that needs to be redone, and the cost of a new roof spread across its life is lower than the cost of a decade of call-outs. The cost side is set out in how much a new roof costs in the UK, and the work itself in the re-roofing process.

Where timbers are soft once the covering is off, the plan widens to include them, and rotten roof timbers explains what that involves.

The next step is a survey. We go up, look at the covering and the details, check the loft, and send pictures of your own roof, so every comment can be matched to something visible. One total price follows in writing, and when the better answer is a repair, that is the advice you get.