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Where's all this moss coming from?

While looking through some old photos (late 80s to 90s), it caught my eye that in the background many of the roofs that were visible were all virtually spotless. You can drive to any housing estate more than a couple of years old, or to any house on its own in the countryside nowadays and you'll do well to find one that is not either green with moss and algae or covered in yellow lichens.
Remove unsightly growths safely with damage to the roof materials.
So why all of a sudden, in the space of a few years is there so much moss, algae, lichens and other growths present on not only roofs but other external surfaces like walls and paths?
My first thought was climate change, but surely there hadn't been that much of a change in such a short time. After looking into a bit more it slowly began to make sense.

Governments across the world, including ours here in Ireland, have been working for some time now on regulations and directives brought about by what they call 'the clean air act'. This is something that, especially in the last few years, has always been high on the agenda of these big 'summits' that seem to happen a lot lately.
Moss, algae and lichens are just a bit of proof that the measures these governments are taking to clean up the air we breathe, are actually working.

New Roof. Fibre cement slating. Moss prevention. 
Loais Its widely known in the roofing industry that copper strips placed under a ridge, can go a long way towards preventing these growths (an expensive, and not 100% effective method in my opinion), due to the sulphars that are released from the copper oxidizing when wet (not perfect wording, I'm no chemist, as you can tell) It was these sulphuric acids and other pollutants that have been present in the air and rain for many years that were keeping the roofs and other external surfaces all along...

Simple really when you think about it. The part I found hardest to get my head around was the fact that the government actually seem to be getting something right! Ah boy Enda!

1 Comment to Where's all this moss coming from?:

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Francois Moal on 09 May 2012 16:28
The most common explanation is "clean air". Leaded petrol and acidic rain were keeping algae away. I am not sure if the clean air accounts for everything, but it is a contributing factor.
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