The black streaks are also known as black algae or roof mold.
Black mold on slate roof.
At worst they can pose serious health risks.
Just because you can t see it however doesn t make it any less dangerous.
Slate is a sedimentary rock with miniscule layers that easily cleave.
Once turned into roofing material slate absorbs water and can naturally de laminate during the freeze and thaw cycles of winter.
Slate is one of the most durable and popular materials used in construction.
Technically the black streaks on roofs are a form of algae known as gloeocapsa magma.
This quality is what distinguishes slate as a suitable roofing material.
Commonly found in climates with warm humid summers it does no damage to the roofing but it certainly does looks bad.
The black mold like stains and streaks that appear on roofs particularly light colored asphalt shingles is actually a blue green algae gloeocapsa magma.
It s easy to let a mold problem sneak up on you on in out of the way places like the roof of your home.
Like all tile however slate can be prone to mildew and mold particularly if it is installed in a high moisture area like a bathroom a basement or a kitchen.
At best slimy black mold deposits are an eyesore.
For this reason it works as well on a tiled roof as it does on a bathroom floor.
Those that tend to be the most humid furthermore they will only appear on the north side of the roof.
What are those ugly black streaks on my roof.
The most common type is known as gloeocapsa magma also known as blue green algae.