Why the Vocabulary Matters

If you own a Victorian terrace, a Georgian townhouse or a stone-built cottage, you have probably discovered that old roofs do not behave like modern ones. They were built with layers, overlaps and hand-cut details that rarely appear on a new-build estate. When something goes wrong and you call in a roofer, the conversation can feel like it is happening in another language. Understanding a handful of terms puts you back in control. You can ask sharper questions, spot when a quote is vague, and describe what you are actually seeing from the bedroom window.

The Structure Beneath the Slates

On most older properties, the visible slates are only the outer skin. Beneath them sits a framework that does much of the real work.

• Battens: The horizontal strips of timber nailed across the rafters. Slates are hung on them, with each course overlapping the one below. In older roofs these are often slightly irregular in spacing, which is why replacements need care.
• Sarking: Boards laid across the rafters underneath the battens, common in Scotland and on some older English roofs. Sarking adds rigidity and can act as a secondary barrier, but it also means trapped moisture has fewer places to escape.
• Rafters and purlins: The sloping timbers that form the roof's skeleton. Purlins run horizontally to support the rafters; if they sag, the slate courses above can crack or slip.
• Underlay or felt: A modern addition on many re-roofs. Traditional roofs often had nothing between slates and rafters, relying on ventilation and overlapping courses instead.

If a roofer mentions "stripping back to the battens", they mean removing the slates and examining that hidden layer. It is often where the real problems live.

Slate Types, Sizes and Fixings

Not all slates are equal, and the differences affect both cost and lifespan.

• Natural slate: Quarried stone, typically Welsh, Cumbrian or imported. It can last well over a century when correctly laid.
• Reconstituted or fibre cement slate: Manufactured alternatives that are cheaper and more uniform. Fine on a modern extension, less sympathetic on a listed or period roof.
• Graduated slates: Courses that decrease in size towards the ridge, common on older properties. Reproducing this pattern takes skill and should be specified clearly.
• Nails and hooks: Traditional slates were fixed with copper or galvanised nails, or hung on wooden pegs. Rusted nails are one of the most common causes of slipped slates on old roofs.

When a roofer says slates have "gone", they usually mean the fixings have failed rather than the slate itself. That distinction matters, because re-nailing can be cheaper than full replacement.

Flashings, Valleys and the Awkward Bits

Water is patient. It finds every junction, which is why the details around chimneys, walls and roof intersections cause more leaks than the main field of slates.

• Flashing: The metal or leadwork that seals the join between the roof and a wall or chimney. Lead is traditional; modern alternatives include aluminium and flexible compounds.
• Apron and cover flashing: The apron sits at the base of a chimney, while cover flashing, sometimes called stepping, runs up the side in stepped sections following the mortar lines.
• Valley: The internal channel where two roof slopes meet. Valleys take the heaviest flow of water on the roof and are usually lined with lead, copper or GRP. A blocked or cracked valley shows up as damp patches far from the obvious source.
• Ridge and hip: The ridge is the top line of the roof; a hip is a sloping edge. Both are bedded in mortar or fitted with dry ridge systems, and both are vulnerable to frost damage.
• Verges: The edges where the roof meets a gable wall, often finished with mortar or a verge board. Loose mortar here lets wind-driven rain straight under the slates.

Terms You Will Hear About Damp and Ventilation

Old roofs were designed to breathe. Modern insulation and airtightness can upset that balance, so it helps to know the words used to describe the symptoms.

• Breathability: The ability of traditional materials to let moisture vapour pass through rather than trap it. This is why cement render and plastic paints can cause problems on old walls and roofs alike.
• Condensation: Moisture from inside the house condensing on cold timbers or underlay. Often mistaken for a leak, especially in winter.
• Inglenook and chimney stack: The large masonry stacks typical of period homes. They need leadwork and a sound flaunching, the mortar cap that sheds water away from the top.
• Torching: Mortar applied to the underside of slates on some traditional roofs. It can crumble with age and block ventilation, and many roofers now advise against renewing it.

Getting the Most From a Roofer's Visit

Armed with these terms, you can have a far more productive conversation. Ask which specific slates have failed and whether the battens are sound. Ask whether a repair will match the existing slate size and colour. If a valley or flashing is involved, ask what material will be used and how it will be dressed over the adjacent slates.

A good roofer will welcome the questions. If someone speaks only in generalities, or quotes for a full re-roof before explaining what is actually wrong, it is reasonable to seek a second opinion. Old roofs reward patience and informed maintenance, and the more clearly you can describe what you see, the better the repair will be.