Does anyone know what this is?

[Ruben1980]

I'm looking at purchasing a property. It's only 10 years old. There is black covering exterior side wall, which is west facing (see the two pictures below). The back and front exterior walls only have very little black. The interior of the house is well maintained, no visual signs of mould or smell. There have been 3 roof leaks that have been fixed since it's been built, none of them serious. Is this likely to be black mould and how bad could it be? The other properties on this development have similar black covering. The properties are not near a busy road. Other properties next to the development don't seem to have the black marks.

Thanks for your thoughts.