Late September is a gift to anyone with a slate roof. The days are still long enough to see what you are doing, the slates are dry, and the worst of the weather is a couple of months off. Leave it until December and the same small faults — a slipped slate, a blocked valley, a cracked mortar fillet — turn into a stain spreading across a bedroom ceiling and a repair bill several times what it needed to be.
The good news is that slate is one of the most forgiving roof coverings there is. It does not rot, it does not tear, and individual slates can usually be replaced without disturbing their neighbours. What lets a slate roof down in winter is almost always the details around it: the gutters, the flashings, the fixings and the ventilation. Those are the things worth an afternoon of your attention now.
Start with a Slow Walk Around the House
Begin at ground level, on a dry day, and work your way around the building. Take a pair of binoculars — a cheap pair is fine — and stand back far enough to see the whole slope rather than craning your neck under the eaves.
What you are looking for is anything out of line. A slate that has slipped down and sits proud of its neighbours. A gap in the courses where one has fallen out altogether. Moss or grass growing in a valley, which holds water against the slate. Ridge or hip tiles that have shifted, or a mortar line that has crumbled away to dust. On a roof with a long history, look for patches where the colour changes: it often marks an older repair that may or may not still be sound.
Then go inside the loft with a torch. Daylight coming through the roof covering is worth investigating, as is any dark staining on rafters, on the chimney breast, or on the underside of the membrane. Water marks on stored boxes and suitcases are a reliable sign that something is getting in, even if the ceiling below still looks fine.
Write down what you find. A list of specific faults is far more useful to a roofer than "there's a leak somewhere at the back".
Clear Gutters, Downpipes and Valleys
A slate roof sheds water quickly, and that water has to go somewhere. When gutters and valleys are blocked, it goes into the eaves, down the walls and into the foundations instead. Overflowing gutters are behind a surprising amount of the damp blamed on roof coverings.
Late autumn is the right moment, once most of the leaves are down, and again after any big storm. Clear:
- gutters along the eaves, including behind hopper heads;
- downpipes, checking that water actually runs away rather than backing up;
- valleys, particularly where a slope meets a chimney stack or a lower roof;
- gully or soakaway at ground level, which is easy to forget and often the real blockage.
Also check that gutter brackets are still holding the run at the correct fall. A gutter that has sagged or pulled away from the fascia will spill water against the wall no matter how clean it is. Clearing gutters from a ladder is a two-handed job that most people try to do one-handed; a gutter vacuum, a long reach pole, or paying someone who does it every week is money well spent.
Repair Slipped, Cracked and Delaminated Slates
Slates fail in fairly predictable ways. On older roofs, the nails corrode and the slates slide out of position. Some types of slate delaminate, flaking away in thin layers until they are too thin to survive a gale. Others simply crack, often from a foot placed in the wrong place during an earlier repair.
A single slipped slate is not a small problem. It opens a gap in the covering that lets water onto the battens and membrane, where it can travel sideways before finding a way through. If you can see several slipped slates from the ground, assume there are more you cannot see.
Do not walk on the roof to deal with this yourself. Slate is brittle, wet slate is treacherous, and a slipped slate is a job for someone with the right access equipment. A good roofer can often refix or replace individual slates from a ladder or a small tower, using a slate hook or a strap where the original nail has gone.
Check Flashings, Mortar and Ridge Lines
Flashings are where most winter leaks begin. Lead aprons, soakers and cover flashings around chimneys, abutments and valleys take a lot of movement over the years, and lead that has cracked, split or been lifted by wind will let water straight through.
Mortar fillets are just as vulnerable. Freeze-thaw cycles are hard on cement: water sits in a hairline crack, freezes overnight, expands, and widens the crack a little more. By spring the fillet has gone. The same applies to ridge and hip tiles bedded in mortar. If you can see crumbling mortar from the ground, it needs repointing before the frosts arrive properly, and preferably by someone who knows how to do it so it lasts.
Be sceptical of silicone sealant applied along a flashing. It buys a season at best and hides a problem that will still be there next autumn.
Ventilation, Insulation and Ice Dams
Ice dams form when heat escaping from the house melts snow on the upper part of the roof, and the meltwater refreezes at the cold eaves. The ice builds into a ridge that traps water behind it, which then backs up under the slates. It is more common in colder countries than here, but a hard UK cold snap with lying snow is enough to cause it.
The cause is usually in the loft, not on the roof. Check that loft insulation has not been pushed into the eaves, blocking the ventilation path. A gap of roughly 25mm at the eaves should be maintained, and if the insulation is deeper than the joists, use trays or baffles to keep the air moving. Check too that any extract fans are ducted outside rather than discharging warm, damp air into the roof space, where it will condense on the underside of the slates.
Prepare for Wind Before It Arrives
Most UK storm damage to slate roofs is wind damage. Loose ridge tiles become missiles, weakened slates lift and shatter, and branches that have been rubbing against the roof all summer finally come down on it. A few jobs now reduce the risk considerably:
- Cut back any branch within a couple of metres of the roof covering, ideally in late autumn and again in spring.
- Check that repairs from last winter's storms were done permanently, not just made safe.
- Look at the verges and gable ends, where wind gets underneath and prises the edge of the covering up.
- Note the name of a roofer you would trust before you need one in a hurry after a gale.
Know Your Limits, Then Put It in the Diary
Everything above can be done from the ground, from a ladder at gutter height, or from inside the loft. Anything that involves standing on the slates is a job for a professional with proper access and insurance, and that is not a matter of caution for its own sake — a fall from roof height is serious, and an uninsured repairer working on your roof can leave you carrying the consequences.
So set the work out over the next few weekends, in this order:
- Walk round, look up, write a list.
- Clear the gutters, downpipes and valleys after the leaves have fallen.
- Get a roofer out to price the slipped slates, flashings and mortar while the weather is still workable.
- Fix the loft ventilation before the cold arrives, not after the first leak.
- Cut back the trees and save a roofer's number where you can find it in the dark.
An hour or two now, on a bright afternoon with a mug of tea and a notepad, is the difference between a roof that shrugs off the winter and one that keeps you up in February listening for drips.
Photo: Olivia / Pexels
