Chapter 1: Why are slates sliding off the roof of our Victorian terrace in Reading?
What we find
A Welsh slate roof is built from thin stone sheets, each hung from two nails and covered by the slate above it. When the roof is a century and a half old, the nails are usually the part that has aged worst. Iron corrodes in the damp that collects under slates, the shank thins, and the slate slips an inch or two. Then it hangs from one nail, then none, and drops into the gutter or onto the path below.
On streets like those off Oxford Road, where the council describes roofs as almost entirely slate, one house after another may show the same pattern. Look from the pavement for dark gaps, slates that sit crooked, or stone chips in the gutter. Inside, a brown mark on an upstairs ceiling below a missing slate is typical, and in the loft you can sometimes see daylight where the felt has long since perished.
What we fix
Individual slates are replaced from above without disturbing the course around them: the broken one is cut out, a strip of lead or a stainless hook is fixed to the batten, and a matching slate slides in. We hold each replacement against the roof to check thickness and tone, and reclaimed Welsh slate is our first choice where the street can see it. If a whole slope is losing slates, the nails have gone and the honest answer is a strip and re-lay on new battens, reusing the sound slates.
For a typical UK range, natural slate re-roofing is reported from £120 up to £180 a square metre, and Welsh slate from £140 to £180. Those figures are guides taken from UK price surveys, and our own number comes only after the photographs. Our slate roofing page sets out when repair stops making sense.