Stone slate is heavy, durable and laid in a sequence that takes years to master. Cotswold District Council's technical guidance for owners, published in 2000, notes that a quarried block splits into several small stones for each large one. Hence broad stones sit low on a Horsley slope and narrow ones climb towards its crest, a pattern called diminishing courses. That guidance puts the load at about 1000 kg for every 10 square metres of roof.
Q2.1When is a slope relaid rather than patched?
Patching suits a roof in which a handful of stones have slipped and the pegs and battens elsewhere are sound. Relaying suits a roof where the fixings have failed across a slope. The stones are lifted, sorted by size, laid out on the ground and put back on new battens with new pegs, with any broken ones replaced by matching stone. Our page on repairing or relaying a stone roof goes through the choice in more detail.
Q2.2Why does the type of stone matter?
The guidance names two limestones used for slates, Forest Marble and Stonesfield Slate. It also reproduces English Heritage policy: sandstone and limestone should never stand in for each other, second-hand stone is best used only on the building it was taken from, and new stone is preferred where it can be had. So before suggesting any replacement, we ask what the existing covering is and where it came from.
If the roof is something else entirely, such as clay tile, slate or concrete, the same approach applies: find the fault, repair what can be saved, and put the smallest sound answer into a written quote. Many Horsley homes have had more than one covering over their lives, and a survey sorts out which is which.