Those dark streaks on your roof are alive, and they shorten its life. What they are, and why you should never pressure wash a roof to get rid of them.
The black streaks running down so many Florida roofs are a living organism, and in Northwest Florida most roofs need a gentle soft wash about every 24 months to keep them away. If your roof looks older than it is, this is probably why.
What are the black streaks?
They are a type of cyanobacteria often called Gloeocapsa magma. It lives on asphalt shingles and feeds on the limestone filler inside them. That is why the streaks run downward: the colony spreads with the rainwater.
Are they damaging my roof?
Slowly, yes. The dark growth holds moisture, absorbs more heat and keeps feeding on part of what the shingle is made of. Left for several summers, it shortens the life of the roof — and it is often the reason an HOA sends a letter.
Should I pressure wash my roof?
No. This is the most expensive mistake homeowners make. The granules on a shingle are what protect it from the sun, and high pressure knocks them off. Once they are in the gutter, no cleaning can put them back. High pressure can also drive water up under the shingles.
How is a roof cleaned properly?
- Plants are soaked first so the cleaning solution cannot harm them
- The solution is applied at low pressure — under 500 psi — and left to work
- The roof is rinsed gently, working downslope
- Gutters are cleaned outside in the same visit, so the streaks do not stay on the gutter face
A typical single-storey roof takes 2 to 3 hours. One thing to expect: the growth dies within the hour, but the dark stains fade over the next 5 to 10 days as sun and rain finish the job.
How can I tell if my roof needs it now?
Stand across the street and look at the north side of the roof. If you can see dark streaks from the sidewalk, it is time. Roofs under trees usually need it every 18 months; roofs in full sun can go longer.
Does a roof cleaning help with the electric bill?
Dark growth absorbs heat, so a clean roof reflects more of it. We will not promise a number — it depends on the house — but a clean roof does not work against your air conditioning the way a streaked one does.
A clean roof is not vanity. It is maintenance on the most expensive surface you own.
Read more on our roof cleaning page, or ask for a free estimate.
