Slate roofs get replaced too early more often than too late. The covering and the fixings have wildly different lifespans, and confusing the two is expensive.
Cadw's study of Flint records that slate dominates the town's roofscape, particularly machine-cut later nineteenth-century slate. Machine-cut slate of that period is a durable product, and that fact is the source of most of the confusion about when these roofs need replacing.
The confusion is this: people treat “the roof” as one thing with one lifespan. It is not. It is several systems stacked on top of each other with wildly different lifespans — and the one you can see from the street usually lasts longest.
| System | What it does | Typical life |
|---|---|---|
| The slates | Shed water | Longest by far — a century and often much more |
| The fixings | Hold the slates on | Decades; the usual first failure |
| The battens | Carry the fixings | Decades; fail with water or old nail damage |
| The underlay | Second line of defence | Shortest, in older bitumen felt |
Read that table again, because it contains the whole answer. Three of the four systems will need renewing several times before the slates themselves are worn out. A roof that is failing is usually a roof whose fixings, battens and underlay have gone — with a covering on it that has decades left.
Slates slipping in ones and twos, in different places, over several years, with no storm to account for them.
Every nail on the roof went in at the same time and has sat in the same conditions since, so they corrode at broadly the same rate and fail together. Once it is general there is no repair: the slates either side of the one you refix are on the same clock, and you pay for access every time.
Visible from the loft on a bright day. Old bitumen felt goes brittle and tears, particularly at the eaves where it has been carrying water and taking daylight through the gutter gap. Once it has gone, a slipped slate is a leak indoors rather than an inconvenience.
Split along the nail line, or soft where water has been sitting. If the battens have gone, everything above them has to come off to renew them.
Press the rafter ends where they meet the wall plate — the first place to go, because that is where a failing gutter deposits water. Soft timber there means the job has grown beyond roofing.
A different question, and the one that decides whether you are buying new slate or relaying your own.
A handful of poor slates on an old roof is entirely normal and means nothing. What matters is the proportion. Where most of the roof rings sound and looks solid, the slates are worth keeping.
If the roof has failed but the slates are sound, there is a third route between patching and a full new covering: strip the roof, renew the battens, underlay, fixings, lead and insulation, and relay the original slates.
It is not cheap — every slate is handled twice, sorted, graded and re-holed, and you buy in material to cover the losses. But it can come in below a full roof of new slate, and it keeps the appearance of the building exactly as it was. On a terrace where the neighbours are unchanged, and inside a conservation area, that is worth more than the arithmetic alone.
It is worth asking for it to be priced alongside a new covering, so you can see the difference rather than assume it.
Everything above pushes towards not replacing a slate roof prematurely, and that is the right instinct. But there is a real cost to leaving it too long, and it is not about the slates.
Once the underlay has perished and the fixings are going, water reaches the battens and then the rafters. At that point the job stops being a re-roof and becomes a re-roof plus carpentry — and the slates you were protecting get handled during structural work rather than a clean strip, which is when breakage rates climb.
The sweet spot is the point where the fixings have clearly gone but the timbers are still sound. That is when the slates come off cleanest, the survival rate is highest, and the job is purely roofing.
Flint is in Wales, and the position is not the same as it is across the border. Planning: section 55 of the Town and Country Planning Act 1990 applies in Wales as well as England, so a like-for-like re-roof is not development at all and needs no permission. But Wales never adopted the 2015 permitted development order that applies in England — it still uses the General Permitted Development Order 1995, as amended.
Building regulations: regulation 23 of the Building Regulations 2010 applies in England and Wales alike. Where more than 50% of the roof's surface area is renewed, or the work forms part of a major renovation, the roof must be brought up to current thermal standards so far as that is technically, functionally and economically feasible. A patch repair does not trigger it, and neither does a roof over unheated space such as a detached garage.
If your slates have years left in them, we will tell you — and price the job that keeps them.
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