Slate roof repair in Lewisham
Lewisham is full of Victorian and Edwardian slate roofs, most of them original. Slate itself lasts a very long time. The nails holding it on do not — and that distinction determines whether you need a repair or a re-roof.
If slates are slipping off your roof, the useful question is not "how do I put that one back" but "why did it come off, and are the rest about to do the same". This page explains how to tell.
Nail fatigue: the defining problem of a Victorian slate roof
Slates are hung on nails. On roofs of this age those nails are typically iron, and iron corrodes. Over a century or so the nail shanks rust through, and the slate — still perfectly sound in itself — simply slides off.
This is called nail fatigue or nail sickness, and it has a characteristic signature:
- Slates slip one or two at a time, at intervals, in different places across the slope
- The fallen slates are usually undamaged — they are not broken, they have just come loose
- It accelerates over time: one a year becomes several a year
- It typically affects a whole slope, because the nails all went on at once and are all the same age
That pattern matters enormously, because it changes the economics. Refixing individual slates on a roof with widespread nail fatigue is a treadmill: each repair is cheap, but you will be paying for access repeatedly, and the pace increases.
Repair or re-roof — the honest test. If slates are slipping in isolated spots and the fallen ones are broken rather than intact, you have localised damage and a repair is the right answer. If intact slates are slipping in scattered places at an increasing rate, you have nail fatigue and are approaching a re-roof, whatever anyone patches in the meantime. We will tell you which pattern we can see — including when it is the first one.
The other things that go wrong with slate
- Delamination. Slate is a layered stone, and at the end of its life it starts splitting along those layers. Slates go soft, flake and lose their edges. Unlike nail fatigue, this is the slate itself failing and cannot be repaired — only replaced.
- Broken slates from impact: a falling branch, a dropped tool, scaffolding, or someone walking on the roof. Almost always localised, and a straightforward repair.
- Previous bad repairs. The most common thing we correct. Slates "fixed" with mortar dabs, foam, bitumen or exposed nails through the face — all of which trap water, damage neighbouring slates and fail again quickly.
- Perished underlay. The bitumen felt beneath the slates becomes brittle and tears, so water that gets past the covering is no longer caught. Visible from the loft.
- Failed valley, ridge or verge details, which are mortar and lead problems rather than slate problems. See ridge and verge repair.
- Torching failure. Some older roofs were finished internally with lime mortar between the rafters. As it crumbles it drops into the loft and stops doing its job.
How slates are properly refixed
You cannot simply nail a replacement slate back in the middle of a slated slope — the course above covers the fixing point. A slate must be held by a tingle (also called a slate hook or clip): a strip of lead or copper nailed into the batten below, bent up over the bottom edge of the new slate to retain it.
Done properly, a tingle is barely visible and lasts. Done badly — or replaced with mortar, mastic or a face-fixed nail — it creates the next problem:
- Mortar dabs hold water against the slate and crack off within a couple of winters
- Face-fixed nails put a hole through the slate exactly where water runs
- Mastic and foam trap moisture, degrade in UV, and make later proper repair harder
If someone has previously "repaired" your roof this way, expect to be dealing with it again.
Matching slate on a period roof
Slate is not one material. Welsh slate, Spanish slate and reclaimed stock differ in colour, thickness, texture and how they weather. On a terraced street where the roofs are visible from the pavement, a patch of mismatched slate is permanent and obvious.
For repairs on period property we would normally use reclaimed slate of matching size and type where we can source it. Sizing matters as much as colour — slates come in a range of dimensions and the wrong size disrupts the coursing and the headlap, which is what keeps water out. This matters most on the consistent Victorian terraced rooflines north of Catford and around Blackheath, where a mismatched patch is visible from the street permanently.
Slate and chimneys
The area around a chimney stack is where slate roofs most often leak, because it is where the covering has to be interrupted and detailed around masonry. Slipped slates near a stack, or a repair around the base of one, frequently turn out to be a flashing problem rather than a slate problem. See chimney flashing repair and roof leak repair.
Do not walk on a slate roof. Slate breaks under point loads and offers no grip when damp. Walking on it to inspect or retrieve a slipped slate reliably creates more damage than it resolves, and slate roofs are steep. Access needs to be from a ladder, a tower or a scaffold, working off the roof rather than on it.
Losing slates?
Tell us how many, over what period, and whether the ones that came down were broken or intact. That is genuinely the information that determines the answer.
Slate questions
How long does a slate roof last?
The slate itself commonly lasts a century or more — good Welsh slate considerably longer. The limiting factors are the nails, the battens and the underlay, all of which have shorter lives. That is why so many Victorian roofs are re-covered using a substantial proportion of their original slate.
Can slipped slates be put back, or do I need new ones?
If the slate came off intact it can usually be refixed with a tingle. If it broke on the way down, or is delaminating, it needs replacing. Either way the fixing method matters more than the slate — a correctly fitted tingle lasts, a mortar dab does not.
Is it worth repairing a roof with nail fatigue?
For a while, yes — particularly if the roof otherwise has life in it and you need to spread the cost. But go in knowing what you are buying: repairs on a nail-fatigued roof are a holding measure, and the interval between them shortens. The honest calculation is repair cost multiplied by expected frequency, against the cost of doing it once — worked through on the roof repair cost page.
Can a slate roof be repaired in winter?
Slate refixing itself is not especially weather-sensitive — it is a mechanical fixing, not mortar. What limits winter work is safety: wet or frosted slate is dangerous to work near, and high winds stop work at height. Mortar-dependent elements such as ridge bedding do need frost-free conditions.