Using slate cladding to update external walls

Why slate cladding suits British walls

British weather is unforgiving in a very particular way. It is not the cold that wears a wall out, it is the driven rain that arrives sideways in November and stays in the render until March. Anyone who has watched pebbledash turn green, or repainted a timber-clad gable three times in a decade, understands the appeal of a facing material that simply sheds water and gets on with it.

Slate cladding does exactly that. It is a ventilated rainscreen rather than a waterproof barrier, which is the key point to grasp before you buy anything. Water is kept out by the slate, drainage and ventilation happen in the cavity behind it, and the breather membrane handles what little moisture gets past. Get the order right and the wall dries. Get it wrong and you have built a very expensive sponge.

Slate also sits happily beside traditional materials. A blue-grey slate panel on a rendered 1930s semi, or riven slate beneath a stone lintel on a cottage, reads as deliberate rather than pasted on. Unlike timber, it needs no re-oiling, and unlike render, it will not crack along the corner beads.

Choosing the right slate for a wall

Roofing slate and cladding slate are relatives, not twins. Roof slates are commonly 4–6mm thick because they lie flat and shed water downwards. Walls catch rain at every angle, so cladding slates are usually 7–9mm, sometimes thicker, and they need to resist impact as well as water.

• Riven edges give a rustic, hand-dressed character that suits stone cottages and older brick.
• Sawn and bevelled edges give crisp, even lines that work well on contemporary extensions and garage conversions.
• Colour varies from blue-grey to heather purple and grey-green. Order everything as one batch where you can, because slate from different seams will never quite match once it is on the wall.

Check that the slate is certified to BS EN 12326, and confirm its water absorption and carbonate content — high carbonate slate is prone to weathering and should not go on an exposed west-facing elevation. Expect roughly 30–40kg per square metre once fixed, which is worth checking against a timber-frame wall or an ageing lintel.

Fixing methods and what goes behind the slate

Most slate cladding is secret-fixed with stainless steel or copper hooks onto horizontal battens. Hooks let you replace a single broken slate without stripping a panel, which matters enormously in twenty years' time. The alternative, face-fixing with screws or nails, is quicker and cheaper but puts the fixing on show and makes future repairs fiddly.

The build-up behind the slate should follow a consistent pattern: sheathing or masonry wall, breather membrane, vertical counter-battens, then horizontal treated battens at 25 x 50mm. The counter-battens create a drained, ventilated cavity of around 25mm. Leave the top and bottom of that cavity open, with insect mesh to keep the wasps out.

Use stainless steel or copper throughout. Galvanised fixings look fine for a few years and then stain the slate with rust streaks, particularly within a few miles of the coast. Set head laps generously — for a 600 x 300mm slate, a 50mm head lap is a sensible minimum, and wider in severe exposure zones.

Detailing, ventilation and damp

Slate cladding lives or dies on its details. At the base, stop the slate at least 150mm above ground level and finish with a drip so water cannot track back onto the wall. At openings, use properly dressed lead or aluminium flashings rather than relying on mastic as a primary seal.

Ventilation matters inside as well as out. If you are cladding over a solid masonry wall, do not then seal the interior with cement render or vinyl silk paint — the wall needs to dry inwards as well as outwards. This is where slate cladding pairs naturally with a lime-based maintenance approach: breathable pointing, breathable finishes, and gutters that actually work.

One useful side effect: slate is non-combustible. For external walls on taller buildings in England and Scotland, where non-combustible materials are required, slate with mineral or metal fixings sails through, unlike many timber and polymer alternatives.

Living with slate, inside and out

The best slate schemes tie together the whole property rather than stopping at the front elevation. A slate roof above and slate cladding below gives a coherent palette, particularly on dormers and porch returns where the two meet. Where a slate-clad wall meets a stone floor at a doorway, a slim stone threshold or a band of matching flags makes the transition feel intentional rather than accidental.

Maintenance is genuinely modest. Clear gutters twice a year, check flashings and copings each autumn, and inspect accessible fixings every five years. Clean slate with a soft brush and water — pressure washing can lift the surface and open up joints, which rather defeats the point of installing a hard-wearing material.

Cost, consent and getting it right

Budget is broadly comparable to good quality brickwork. Expect roughly £120–£180 per square metre supplied and fitted, with riven slate at the upper end and imported slate at the lower. Add access costs on two-storey work; scaffolding is often the largest single line on the quote.

Consent is the part people forget. In a conservation area, permitted development rights for cladding external walls are usually removed, and any listed building will need listed building consent for a change of this kind. Speak to your local planning authority before ordering materials, and if the building is traditionally constructed, take advice on breathability before you commit.

Done properly, slate cladding is a fifty-year decision rather than a five-year one: no repainting, no re-rendering, and a texture that improves as the rain washes it.