Norway day11

I've been here for 10 days and what's bugging me is that almost every bus stop has a grassy roof. Now I can understand the old houses in the woods that have this, and other older buildings - but still not sure why- but bus stops?


Does it happen naturally? Is it cultivated? If so do you buy a packet seed selection of moss, lichen and grass for your bus stop roof? It doesn't stop at bus stops either - wheely bin shelters, village notice boards, garden sheds.
Answers on the back of a £10 note please