Seasonal checks to keep slate roofs weathertight

A slate roof is one of the most durable things you can put over a British home, but durable is not the same as invulnerable. Between driving rain, freeze-thaw cycles, autumn leaf fall and the occasional named storm, even a well-built roof is in constant negotiation with the weather. The faults that cause expensive damage inside – stained ceilings, sodden plaster, damp creeping across stone floors – almost always begin as something small and visible from the ground.

A seasonal routine, done properly, takes a few hours a year and catches most problems while they are still cheap to fix.

Start with the roof, not the ceiling

Water is a patient traveller. A single slipped slate or a hairline gap in a flashing can let water in at the top of the house and have it appear three metres away, often as a brown ring on a bedroom ceiling or a dark patch on a stone floor far from the roof.

That is why traditional maintenance is about inspection rather than reaction. Check the outside of the building regularly, and you will rarely be surprised indoors.

Autumn: gutters, downpipes and the first line of defence

By late November, most deciduous trees have finished shedding, so a gutter cleared in early December tends to stay clear through the worst of the winter. This is the single most valuable job on the calendar.

Blocked gutters do not overflow politely over the edge. Water backs up, sits against the fascia, soaks into the wall plate and tracks down inside the cavity or the solid wall. You often see the result first as damp at the top of a wall, blown plaster, or staining on a stone floor below. Downpipes and hoppers matter just as much: a hopper full of moss and twigs sends water down the outside of the pipe rather than inside it, and a blocked gully at the base can back up into the foot of the wall.

• Clear gutters by hand where you safely can, using a standoff bracket so the ladder does not rest on the gutter itself.
• Flush downpipes with a hose and check they discharge freely into the gully or soakaway.
• Look along the gutter line from a distance – sagging sections hold water and will fail sooner.
• Never work alone at height, and never lean a ladder against a slate roof or plastic gutter.

Spring: moss, lichen and a gentle hand

Moss looks harmless and is often the opposite. It holds water against the slate, lifts the edges of tiles, pushes into the gaps between them and gradually silts up the valleys where two roof slopes meet. By the time a valley is full, water has nowhere sensible to go.

Clear moss in spring, when it is soft after winter rain, using a plastic scraper or a soft brush. Work downwards, not sideways, so you do not lift slate edges. Avoid pressure washers on a slate roof: the jet forces water under the slates, strips the surface and can dislodge the very fixings that hold everything in place. If moss keeps returning, a suitable treatment applied carefully can slow regrowth, but it should never replace mechanical clearing.

While inspecting, check ridge and hip tiles and any pointing. Traditional roofs were built with lime mortar, which flexes slightly with the building. Hard cement pointing on an old roof often cracks and lets water in rather than keeping it out.

After a storm: fifteen minutes around the house

Once the wind has dropped, walk the perimeter with binoculars before doing anything else. Look for:

• Slates that have slipped, cracked or disappeared.
• Lifted or missing ridge and hip tiles.
• Damaged or torn lead flashings around chimneys, dormers and abutments.
• Debris in valleys, and slate fragments on the ground or in the gutter – a useful clue to what has come loose above.

Then go into the loft with a torch. Daylight through the roof covering is a clear signal, and so is damp on the underside of battens or sarking, or water staining on chimney breasts and rafters. Note what you find and get it seen to while the roof is still a repair rather than a replacement.

Inside: what plaster and stone floors are telling you

Interior clues are just as valuable. Fresh damp patches on ceilings or upper walls, a musty smell in a spare room, or paint that blisters and flakes are all roof-related until proved otherwise. On stone floors – flagstones, limestone, slate or Victorian tiles – look for persistent dark patches, white salt deposits and a damp chill that never quite dries.

Stone is breathable by nature and traditionally laid in lime mortar over a permeable base. Sealing a damp stone floor to "fix" it usually traps moisture instead, pushing it into the walls. If a floor stays damp after the roof and gutters are sorted, the cause is more likely ground water or drainage, and worth investigating properly.

Building a simple annual rhythm

A short schedule covers most of it: clear gutters in late autumn, tackle moss and check pointing in spring, inspect from the ground after every significant storm, and look in the loft twice a year. Keep a note of anything you spot and when you saw it – patterns become obvious quickly.

For anything above first-floor level, or any work involving a ladder on a slope, use a competent roofer. Slate is unforgiving underfoot, and the cost of a professional check is trivial next to the cost of a wet winter working its way into your ceilings, walls and floors.