Eugene, OR
Eugene's mild, damp weather and the shade from tall firs and maples common around the city create exactly the conditions moss needs to thrive -- making it one of the most moss-prone places in the country for roofs.
Most of the year's rain falls between November and February, giving moss a long, consistent wet stretch to establish and spread.
A roof in full sun dries out between rains; a roof shaded by mature trees stays damp much longer, which is why moss shows up first and worst on the north-facing or tree-covered sections of a roof.
