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Why Gutters and Flashings Deserve Your Attention

Slate is arguably the finest roofing material ever devised for a British climate. It shrugs off driving rain, frost and coastal salt, and a well-laid slate roof can comfortably outlive the people who installed it. But a slate roof is only as watertight as the details around it, and nowhere is that truer than at the gutters and flashings.

These are the parts that take the strain. Gutters gather everything the roof sheds — rain, moss, grit, the occasional dislodged slate — and flashings seal the awkward junctions where the roof meets a chimney, a wall, a dormer or a valley. When they fail, water rarely announces itself politely. It creeps behind the slates, tracks along rafters, and appears as a damp patch on a bedroom ceiling weeks later. On older properties, this quietly rots roof timbers, eaves felt and plaster, and the repair bill climbs far beyond the cost of a morning's maintenance.

The encouraging news is that most of these problems are spotted early with a torch, a ladder and a little patience.

Clearing Gutters: Little and Often Beats One Big Clean

Twice a year is the sensible rhythm — late autumn once the leaves have fallen, and again in spring after the worst of the moss has washed down. If your roof is surrounded by trees, add a third visit in midwinter.

• Work by hand first. Scoop debris out with a trowel or gloved hand rather than flushing it towards the downpipe, which simply blocks the outlet further along.
• Flush and watch. Run a hose from the high end of the run and follow the water. It should move briskly and disappear down the outlet without pooling.
• Check the downpipe outlet every time. A single handful of moss at the hopper can back water up an entire elevation.
• Mind your ladders. Never rest one against the gutter itself — it will crush the profile. Use a stand-off bracket or a ladder mat against the wall.

While you are up there, look at the slates above the gutter. A build-up of moss on a slate roof sheds steadily into the gutter, and a ridge or hip that has gone green is worth treating before the next winter.

Falls, Joints and Fixings

A gutter needs a fall of roughly 1:600 — about 3mm in every 2 metres — running towards the outlet. It is surprising how often a "leaking gutter" is simply a gutter that has been pushed out of level by a slipped bracket or a settled wall. Check the brackets every 600mm on cast iron and closer on plastic, and look for joints that have opened up with thermal movement.

Older properties often carry cast iron, and it is worth repairing rather than replacing. Cast iron outlasts plastic by decades, and it suits the proportions of a period elevation. Where joints weep, renew the gaskets or bolts and reseal properly. Surface rust is cosmetic; deep pitting and flaking are not, and a coat of metal primer followed by a gloss system every few years will keep ironwork sound.

On listed buildings, replacing cast iron with uPVC can require consent, and it will almost certainly be resisted by a conservation officer. Repair is usually the better answer, both historically and financially.

Lead Flashings: The Quiet Workhorse

Lead does the invisible work on a slate roof — aprons, cover flashings, step flashings at abutments, soakers between slates, chimney trays and valley linings. It is chosen because it is malleable, self-healing to a degree, and lasts for many decades. Code 4 lead suits most domestic flashings; valleys and larger trays generally want Code 5.

What goes wrong? Lead lifts where it has not been properly dressed or fixed, splits at a fold that has been worked too often, and corrodes where it sits against mortar or in contact with incompatible metals. It also suffers when a mortar fillet has been used where a proper flashing belongs — a bit of sand and cement smeared against a chimney breast is not a flashing, and it will crack within a couple of winters.

• Look for flashings that have lifted away from the wall, leaving a visible gap.
• Check step flashings on chimney sides — this is where water most often gets behind slates.
• Soakers should sit with roughly 100mm below the slate and a 150mm upstand, set in a straight, tight line.
• Never paint lead. Let it patinate to its natural grey, which is part of the character of a heritage roof.

Copper, Valleys and Secret Gutters

Copper flashings are lighter than lead and develop a handsome green patina over the years, though they need more careful detailing because they expand and contract more. Thin copper of around 0.6mm is typical for flashings; the fixings must allow for movement, and stainless steel is the safe choice throughout.

Keep metals apart. Copper in contact with zinc, aluminium or galvanised steel will set off galvanic corrosion, and run-off from copper can stain and attack other materials below. Use a separating membrane or a coated lead-trap where dissimilar metals meet.

Valleys and secret gutters — the hidden channels behind slates at a roof intersection — deserve particular attention. They block easily with moss and slate fragments, and once water backs up it has nowhere to go but into the roof. Clear them by hand, then test with a slow pour of water from a watering can rather than a fast jet, which can overwhelm the channel and give a false alarm.

When to Call in a Specialist

Clearing gutters and inspecting flashings from a ladder is well within reach for a careful householder. Anything involving roof access on a steep pitch, lead burning, or replacing soakers beneath slates belongs with a roofer who works with heritage slate.

Ask for a written scope of work that names materials and thicknesses — Code 4 or Code 5 lead, copper gauge, fixings — along with photographs before and after. On listed properties, check whether listed building consent is needed before any alteration to rainwater goods or flashings, and talk to the conservation officer early; they are usually far more helpful than people expect.

Twenty minutes twice a year, a torch and a critical eye will save you thousands. Gutters and flashings are the unglamorous heart of a slate roof, and looking after them is the simplest way to keep a heritage roof doing its job for another century.