Repair or replace: how to tell when a roof has actually had enough

Somebody has been up on your roof, come down, and told you it needs replacing. The number they said is somewhere between five and fifteen thousand pounds. You have no way of checking whether they are right, because you cannot see your own roof and the only other person who has looked at it is the one asking for the money.

This is the most common situation I get called into, and it is worth writing down what I look at, so you can look at some of it yourself.

How long a roof lasts

The honest answer is that it depends on what is on it, and the useful answer is a set of rough numbers.

Notice that most of those are longer than people expect. A slate roof in Leeds that went on in 1890 is not necessarily near the end. That is the first thing to hold onto when somebody tells you a Victorian roof has had it.

Here is the thing those numbers do not tell you, though, and it is the part that matters most. On a slate roof, the slate almost never runs out. The nails do.

Nail sickness, which is what is actually wrong with most Leeds roofs

The slates on a Victorian terrace are fixed with iron nails. Over a hundred-odd years those nails corrode. The slate itself is fine, geologically fine, will-outlast-all-of-us fine, but nothing is holding it any more.

You can tell nail sickness from ordinary damage by the pattern:

• Ordinary damage is one or two slates, usually after a storm, usually in one place, often near an edge or a valley where the wind gets under.
• Nail sickness is slates coming out in ones and twos, in different places, across the whole slope, over several years. You fix one and another goes six months later somewhere else.

If that second pattern sounds like your roof, the re-roof quote is probably honest. You cannot repair your way out of nail sickness, because the thing that has failed is on every slate at once. Every repair is buying a few months.

If it is the first pattern, you are being quoted for a roof that does not need replacing.

The other genuine end-of-life signs

Battens. The timber the slates or tiles hang on. When a slate comes off, a roofer can see the batten underneath. If it is soft, split, or crumbling, the fixings have nothing to hold onto and it does not matter how good the slate is.

Felt or underlay. Older roofs may have none, and that was normal. Bitumen felt from the fifties onwards goes brittle and tears, particularly at the eaves where it should be lapping into the gutter. If the felt has gone, wind-driven rain and snow get into the loft even when every slate is in place.

Widespread tile decay on concrete. Interwar concrete tiles are now approaching a hundred years old. When they go, they go across a whole slope at once, because every tile up there is the same age and has had the same weather. Look for grit and fragments washing out of the downpipe, and for tiles that ring dull rather than sharp when tapped.

The roof line itself. Sight along the ridge from the pavement. If it dips or sags, that is structural, and it is a different and more serious conversation than covering.

The signs that sound alarming and usually are not

One damp patch on a ceiling. Water runs a long way before it drips, so the mark inside is rarely under the hole. This is nearly always a flashing, a valley, or one slipped slate. It is a repair.

Moss. A moss-covered roof is not a failing roof. Moss holds moisture against the surface and can lift tiles slightly at the edges, so it is worth dealing with eventually, but it is not evidence that the roof is finished. Anybody using moss as the argument for a re-roof is stretching.

Age on its own. “It is a hundred years old” is not a diagnosis. Plenty of hundred year old roofs in Headingley, Kirkstall and Meanwood are in better condition than fifty year old ones in the suburbs.

A cracked ridge tile or two. Ridge re-bedding is a day’s work, not a re-roof.

What to do when you get a quote you do not trust

1. Ask what specifically has failed. Not “the roof is at the end of its life”, but which component. Slate, nails, battens, felt, structure. A roofer who has actually looked can answer that in one sentence.
2. Ask for photographs. You cannot see your own roof and they can. Any roofer with a phone can take pictures of what they found. Somebody who will not is telling you something.
3. Ask what a repair would cost and how long it would buy. If the honest answer is “eight hundred pounds and two years”, that is useful information and a straight roofer will give it to you even though it is a smaller job for them.
4. Get a second opinion before you commit. Not a third and a fourth, which just produces confusion, but one other person looking at the same roof.
5. Be suspicious of urgency. Roofs that have been quietly deteriorating for fifteen years do not become emergencies during a doorstep conversation. If there is genuine urgency, it is because water is coming in now, and the first job then is making it watertight, not signing for a re-roof.

The middle option nobody mentions

It is not always repair or replace. Sometimes it is replace one slope.

On a terrace or a semi, the front and back of the roof have had different weather for a century. In Leeds the weather comes off the Pennines from the west, so a west-facing slope is often noticeably worse than the east-facing one on the same house. Doing the bad slope now and the other in ten years is a legitimate approach, costs a good deal less in one go, and no salesman will suggest it.

The same goes for a back addition. On the through terraces in Hyde Park, Woodhouse and Harehills, the back addition roof is smaller, lower, and often in worse shape than the main roof. Doing just that is a common and sensible job.

The short version

If slates or tiles are coming off across the whole roof over several years, the roof is telling you it is finished, and a re-roof is money well spent. If you have one leak and one mark on a ceiling, you have a repair, and anybody quoting a re-roof for it is either not looking or not being straight with you.

The difference is usually visible in ten minutes to somebody who knows what they are looking at, which is why a second opinion costs nothing and is worth having.