The short answer
Slowly, then all at once. Welsh slate itself can outlast several generations, but the iron nails, lead edging and mortar-bedded ridges that hold it together wear out sooner. A sound slate on a rusted nail needs refixing, not replacing, so the fixings are the first thing we examine, and the photographs show you what we found.
Appleshaw's church dates from 1836, and the 1911 county history records slate roofs over rough-cast walls. A roof of that age is a useful lesson, because the stone barely changes with time while everything around it does.
Q1.1Why do slates slip when none are broken?
The cause is almost always the nail, and it is the least visible part of the roof. Early slates hung on iron, and iron rusts until the shank thins and the slate sags down a few millimetres, then slides. Owners notice a gap, a dark stain on a ceiling, or a slate on the path. Putting the same slate back on the same type of nail only repeats the failure, so refixing uses stainless or copper fixings, with clips where a slate needs extra grip in a gust.
Q1.2What gives out at the edges of the roof?
Where slopes meet a wall or a chimney, sheets of lead are worked into the joint to keep water out. Lead moves with every temperature swing, and eventually it cracks along the folds. A soaker is a small lead piece slipped under each course of slate at such a junction, and soakers fail too, often unseen. The ridge along the top was traditionally set in mortar alone. Since BS 5534:2014, a ridge set in mortar and nothing else no longer meets the standard, so one re-set today is pinned as well as bedded.
Q1.3Can a church or chapel roof be worked on from the ground?
Rarely. Tall walls and long slopes mean a tower or scaffold, and the access plan is settled before the quote is written, because it shapes both the safety of the job and the cost.
Our slate roofing page goes into sizes and lifespans, and roof repairs sets out the point at which a patch stops being enough.
On a roof like this we climb every slope, photograph each defect and hand you the pictures with the quote, so you can see which slates are finished and which have only lost their fixings.