Chapter 1: Why do slates keep slipping on our older Bagshot house, and can they be refixed?
What we find
A natural slate roof can last a very long time, but the slates are only as secure as the nails holding them. Each slate hangs from one or two nails driven into a timber batten, and the nail head is the only thing stopping it sliding out. Where the nails were ordinary iron or steel, damp air and rain have rusted the shanks thin over the years, and the slate slips an inch or two, or drops into the gutter. Roofers call this nail sickness.
The signs are slates sitting lower than their neighbours, a gap showing a darker strip of batten, or broken pieces in the border below. In the loft you may see a line of daylight, or staining on the sarking (the boards or felt laid over the rafters beneath the slate). The slates themselves are often perfectly sound.
What we fix
We take photographs of the whole slope first, so you can see where the slipping is concentrated. Where it is only a few slates, we lift the course above, remove the failed nails and fix each slate back with a copper or stainless nail, adding a clip or tingle strip if the slate has lost its hole. Cracked slates are swapped for reclaimed ones that match in thickness and colour, which matters in a conservation area.
A single slate repair is typically priced at £100 to £250 labour, plus the slate, and scaffold or a tower adds £300 to £800; your fixed quote follows the survey. If nail sickness has spread across the whole slope, re-laying the roof on new battens is the honest answer, and our slate roofing page explains how that is done.