Slate roofs have been used throughout human history because of the durability and longevity of this material. Slate is derived from shale sediment composed of clay or volcanic ash. Its breakability and its toughness both make it easy to partition into thin but durable sheets. However, quarrying and transporting it was a dangerous and laborious process. Typically, it was dug out of the ground with hand tools, then moved by horse and wagon.
When the Romans invaded Great Britain in 43 AD, they quarried slate and used it to construct the roofs of military forts. Prized for its robustness, slate provided a sturdy material for military installations including the Roman Fort of Segontium (77 AD). Slate was quite expensive, so for hundreds of years only the wealthiest institutions like the monarchy and the church could afford to build with slate.
Famous early buildings built with slate:
- Calder Abbey in Cumbria (1134 AD)
- Conwy Castle (built by King Edward I between 1283 and 1289)
- Dunbarton Castle (slate was acquired to repair the castle roof in 1445)
The first private home with a slate roof was built around 1300 AD in North Wales, England. The material was mostly only used on castles or other military structures at the time due to its high cost.
Technology improves slate quarrying—and makes slate roofs worldwide more accessible
Eventually new technologies were introduced that made acquiring slate much easier. Gunpowder was used to blast slate into more manageable chunks, which were then taken away to be split into thin pieces. This was a much quicker method of slate extraction, but it was extremely dangerous for the workers involved.
In the 1800s, Spain created a quarrying process that was streamlined enough to make slate roofing more cost effective. This process created a revolution in the industry, finally allowing slate to be used for everyday homes. Spain still specializes in this stone and produce almost 90% of European slate roofing.
Britain’s industrial revolution created a huge demand for slate. For example, the invention of the steam engine allowed slate to be moved around the country far more effectively than it ever could by horse and cart. As a result of these new technologies, slate roofs became common throughout Victorian Britain. This rapid industrialization also created a demand for slate throughout much of Europe.
In America, slate roofs were first seen in the 1600s, but the first quarry didn’t open until 1785. This quarry made the material available to general consumers. Still, it was only in the second half of the nineteenth century that slate was mass quarried. Slate production peaked in 1900 but declined as asphalt shingles became common.
In our next post, we’ll talk about slate roofing in modern times.