Moss growth on roofing slates

Hello slate people

Today I am going to talk about moss growth on slates. Mosses are everywhere. They form a rich group of plants that often are the first organism that colonize new environments. They can grow on almost every surface, including fresh rock, and of course, slate. Generally, mosses are considered as a weathering agent in buildings. Their small roots penetrate the rock surface, opening the path for other weathering mechanisms. However, recent studies have focused on their role in green architecture, which integrates plants in buildings, creating greener cities. A group of researchers from the University of Genoa, in Italy, have recently studied the potential of different roofing materials for “green roofs”, in order to create new ecosystems in the cities. These ecosystems would support colonies of plants, birds and insects which would enhance the sustainability and ecology of the cities…the idea is not bad, but my first concern was about maintenance, is this going to be more expensive than a standard roof? and how about leaks? No problem, they say, everything is under control. Maintenance is cheap, and leaks won´t appear if the roof is properly installed (I´ve heard this before!).

This people studied different roofing materials as substrate for moss colonization

capillary matting > cement plaster > lime plaster > terracotta brick > slate > quartzite

Ordered by moss growth on a given surface. We can see that porous and artificial materials are more prone to moss colonization than natural stones such as slate and quartzite. By the way, being the quartzite a metamorphic rock used for roofing, it can be also considered as a roofing slate (remember the explanation for slate vs. roofing slate? not all slates are good for roofing, and not all roofing slates are slates). So we have a bad and a good news. For this purpose, creating green ecosystems on the roofs, our roofing slates are not good due to their low moss colonization potential (this is the bad news). The good news is that roofing slate will keep free of moss and plants longer than any other roofing material. My experience tells me that organic colonization always jeopardizes the waterproofing of the roof, so better keep them far away.

Sorry for the ecosystems.

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