It is important to have a good roof in our land with its oceanic climate, often rainy and windy, a storm raging sometimes. Looking round, we could be tempted to believe the houses have been always roofed with this "blue stone", so great is the number of slate roofs. Slate is a part of Brittany's image, usually blue, but yellow too or even green (in Ploermel). It is difficult to think that, not very long ago, most of the people lived in thatched houses. But as they became wealthier they abandoned thatch for slate to avoid the dangers of fire and to have stronger and longer lasting roofs.

Slate is in competition on the market with many materials : tile, artificial mineral fibre slate, zinc, bituminous products such as asphalt shingle. Its place on the market is due to its qualities :

It is waterproof and presents no porosity or absorption. So it doesn't crack with the action of water frozen in it.

It resists to compression as well as the best granite.

It resists to breaking as well as oak.

It is light.

It is fireproof and can resist to a heat of up to 200° C.

It is acidproof. Chlorhydric acid drops don't cause any effervescence on its surface.

To conclude, a true slate is easy to use, doesn't weather, doesn't keep moss and lasts longer than the other parts of the building.

Another reason that promoted the industry of slate is the invention of hooks to fix the slates to the frame. It decreased the cost of work and brought a technical improvement : water isn't driven under the slates by wind forces.