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Reading the Roof Before You Touch Anything

Slate is one of the most forgiving roofing materials ever laid on a British building. A well-detailed Welsh slate roof can shrug off a century of Atlantic weather and still look as though it was finished last summer. That durability can be deceptive, though. A roof repaired piecemeal over decades often hides a string of small failures that only show themselves after a hard frost or a gale from an unusual direction.

Before you go looking for a ladder, accept one firm rule: never walk on a slate roof. Slate is brittle, and it is slippery when damp even when the surface looks dry. A single misplaced boot can turn a hairline crack into a hole, and a fall from eaves height will ruin your year far more thoroughly than a leak ever could. Everything below is written on the assumption that you will stay on the ground, in the loft, or at a window.

Assessing the Damage from a Safe Distance

Start with a pair of binoculars and a slow walk around the building in good light, ideally after rain when damp patches darken and stand out. Note where the damage sits: a scatter of cracks across the whole slope tells a different story from a cluster near a chimney or valley.

• Hairline cracks across the face of a slate, often near the nail holes or running diagonally from a corner. These let in wind-driven rain and will widen with freeze-thaw cycles.
• Spalled corners and edges, where the slate has laminated and flaked. This is a material failure rather than an impact, and it usually spreads.
• Slipped but intact slates, sitting proud of the course below. Often the nail or the batten has failed rather than the slate itself.
• Missing slates, leaving a gap that exposes the battens, sarking or torching beneath to the weather.

Then go into the loft with a torch. Look for daylight between the slates, damp staining on rafters and battens, and any softness in the timbers. Check for a tide mark on the chimney breast, which points to failed flashing rather than a cracked slate. Photograph everything with the date visible; your insurer and your roofer will both thank you. Whatever you do, keep your weight on the joists, not on the plasterboard.

Finding Slates That Match a Heritage Roof

Slate is not a single material. Welsh, Cumbrian, Cornish, Scottish and Irish slates all behave and weather differently, and many older roofs were laid with a mixture of sources as supplies ran short. Slates imported from Spain or further afield are usually easy to spot by their colour and thickness, and some are already showing their age after twenty years where a good Welsh slate would be barely settled in.

Ask your roofer to match on five points: size, thickness, colour, texture and the position of the nail holes. Imperial sizes such as 24 x 12, 20 x 10 and 16 x 8 inches are common on older roofs, and a 5 mm slate cannot be substituted for a 7 mm one without the repair showing. On roofs laid to diminishing courses, the slates get smaller towards the ridge, so you will need several sizes, not one.

Reclaimed slates from a reputable salvage yard are almost always the better choice for a period building, even at two or three times the price of new. Take a sample down from a broken slate — carefully, from the loft side if you can — and hand it over. Buy a few extra, label them by size and store them somewhere dry. For a listed building, a labelled stock of spares is genuinely worth having.

Temporary Fixes That Buy You Time

Roofers are busiest exactly when you need them most, so a short-term measure that lasts a fortnight is worth having. Work only from a loft hatch, a dormer window or a flat roof you can stand on properly.

• Contain the water inside. A bucket under the drip, a plastic sheet over vulnerable possessions and a closed door will protect the room far more reliably than any attempt to seal the roof from below.
• Sweep the gutters clear with a hook on a pole from ground level. A blocked gutter backs water up under the eaves and turns one leak into three.
• Use a lead tingle for reachable cracks. A slip of lead code 4, about 100 mm wider than the break and long enough to lap over the two courses below, can be eased under the damaged slate from a Velux. It is a genuine weatherproof measure, not a bodge.
• Silicone is a last resort. A smear over a hairline crack might hold a few weeks, but it traps moisture and looks poor on heritage work. Never bed a slate in cement or mortar instead.
• Do not tug at loose slates. If it is holding on, leave it; you are more likely to dislodge the slates either side of it.

When to Stop and Call Someone In

Working at height kills more people in the UK than any other single cause of workplace death, and domestic repairs account for a grim share of that. Stop immediately if the work needs a ladder above first-floor level, if the roof is wet, frosty or windy, if you have no harness and anchor point, or if you would be working alone. The same applies if a ceiling is sagging, if water is anywhere near wiring or a light fitting, or if you can see movement in a chimney stack. In those cases, isolate the electrics to the affected room, move people out, and call a roofer for an emergency make-safe. Ask them to leave a written note of what they did and when.

Records, Consent and the Long View

Repairs that return a roof to its previous appearance rarely need listed building consent, but alterations do — changing slate type, size or colour on a listed building certainly counts, so a quick call to your local conservation officer before work starts is sensible. Keep your photographs, receipts and any make-safe notes together for the insurance claim, and jot down which slopes were repaired and when. A simple roof plan, marked up over the years, is the single most useful document you can hand the next roofer. In spring, when the weather settles and the trade quietens slightly, plan the batch of repairs properly. Done well, with matching slate and sound fixings, one careful week's work can set the roof up for another fifty years.