Assessing the damage and planning the repair

A broken slate on a steep roof is more than an eyesore. It is an open door for rainwater, and on a period property, that water can quickly reach rafters, laths and plaster ceilings. Before you reach for a ladder, assess the problem from the ground. Note the size, colour and thickness of the damaged slate, and check whether any neighbours have slipped or cracked. Traditional Welsh slates are common on UK period homes, but you may also find Delabole, Burlington or Westmorland green. If your roof is steeper than 30 degrees, treat it with respect: steep pitches shed water well but are treacherous underfoot.

Plan the job for a dry, calm day with temperatures above 5°C. Frost, rain and wind make slate work dangerous and reduce the chance of a lasting repair. If the roof is more than two storeys high, or if the pitch is particularly severe, hire a scaffold tower or full scaffolding. For a single slate on a low, steep roof, a roof ladder and a fall-arrest harness may be enough — but only if you are competent and confident. Never work alone.

Safe access on a steep roof

Getting to the slate safely is half the battle. On a steep roof, you cannot simply walk on the slates; they are fragile, slippery and often loose. Use a roof ladder with a pair of wheels that hook over the ridge, and secure it with a strap. A fall-arrest harness anchored to a solid point, such as a chimney or a dedicated roof anchor, is essential. For larger repairs, a scaffold with edge protection is far safer than balancing on ladders.

Equipment to have on hand includes:

• A roof ladder and roof crawl boards to spread your weight
• A fall-arrest harness with a short lanyard
• A slate ripper (a long flat bar with a hooked end)
• A claw hammer and copper nails
• A slate cutter or angle grinder with a diamond blade
• A tool belt and a bucket with a hook

Keep both hands free wherever possible. Wear soft-soled boots that grip, and never carry tools in your pockets where they can fall and damage lower slates.

Removing the broken slate without disturbing neighbours

The key to removing a damaged slate is patience. Do not pry against the slates on either side; they are thin and brittle. Instead, slide a slate ripper under the broken slate until you feel the nail. Hook the nail and cut it by pulling and twisting the ripper. Work from the bottom of the slate upwards. If the slate is shattered, remove the pieces carefully with gloved hands, then brush away any debris.

Once the slate is out, inspect the batten and the underlay. On period properties, you may find no felt at all — just lime mortar torching or sarking boards. If the batten is rotten, cut it back to sound timber and splice in a new piece of treated timber. If the underlay is torn, patch it with a suitable flashing tape. Never leave an open gap.

Sometimes you cannot reach the nail because the slate above overlaps too tightly. In that case, you may need to gently lift the slate above using a wooden wedge or a slate ripper. Do this with extreme care. If the slate above cracks, you have made the job twice as big.

Fitting the replacement slate

Match the replacement as closely as possible: same length, width, thickness and colour. A slightly thicker slate will sit proud and can crack under foot later. If you cannot find a perfect match, a reclaimed slate is often better than a new one of the wrong size. Trim the slate to size with a slate cutter or an angle grinder.

Slide the new slate up under the course above. If you can reach the batten, nail it with two copper nails — never galvanised, which corrodes quickly. Use a short-handled hammer and tap gently. If you cannot reach the batten, use a slate clip (a metal strap that hooks over the batten and holds the slate) or a lead tingle (a strip of lead dressed over the slate and up under the course above). A slate clip is a good permanent repair on a steep roof, but a lead tingle is more traditional for period properties.

Check the headlap: the new slate should overlap the slate below by at least 75mm. Do not bed the slate in mortar. Mortar traps moisture, cracks with movement, and is a common cause of premature failure. The slate should sit flat and secure, with no rocking.

After the repair: long-term care for period slate roofs

Once the new slate is in, take a few minutes to check the rest of the roof from your safe access point. Look for slipped slates, corroded nails, blocked gutters and damaged flashings. On a period property, small problems escalate quickly. Schedule an annual inspection from the ground, and clear gutters every autumn.

Keep a small stock of matching reclaimed slates in the shed. If your home is listed or in a conservation area, check whether you need consent before altering the roof. And if you are ever unsure about access, pitch or the condition of the battens, call a professional roofer. A steep slate roof is no place for guesswork — but with care, a single broken slate is a repair you can handle.