Black Streaks on Your Roof
If dark stains are running down your roof in vertical streaks, you are not looking at dirt, soot, or worn-out shingles. You are looking at a living organism, and it is eating your roof.
What those streaks actually are
The black streaks on almost every stained roof in Central Florida are Gloeocapsa magma — a hardy blue-green algae that feeds on the limestone filler manufacturers mix into asphalt shingles.
It takes hold on the north and shaded slopes first, because those dry slowest after rain. As the colony matures it produces a dark protective sheath against UV light, which is the black you see. The streaking runs vertically because rain carries spores down the slope, seeding new growth as it goes.
Left alone it spreads across the whole roof plane, holds moisture against the shingle, and accelerates granule loss. A stained roof also runs measurably hotter, because the dark colony absorbs heat your shingles were designed to reflect.
Why Central Florida roofs get hit so hard
Our climate is close to ideal for this organism. Sustained humidity, daily summer rain, and mild winters mean there is no dormant season — growth continues year round.
Homes under mature oak canopy in Winter Park, Maitland and Longwood are hit hardest, because shade keeps the shingle damp for hours after a storm. Newer subdivisions in Oviedo, Lake Mary and Winter Springs see it too, just more slowly, since open exposure lets the roof dry faster.
Most Central Florida homeowners see visible streaking within three to five years of a new roof.
What not to do
Do not pressure wash your roof. High pressure strips the ceramic granules that protect the asphalt underneath, voids most shingle warranties, and can force water under the courses into your decking. It also only removes the visible sheath — the colony survives and returns darker within months.
Do not use undiluted bleach from a garden sprayer. Without correct dilution, surfactants and thorough plant protection, runoff will burn your landscaping and etch aluminum gutters and window frames.
Do not wait for a roof replacement to fix it. Algae is a maintenance issue, not a structural failure. Cleaning it is a fraction of the cost of the roof life you lose by ignoring it.
How we remove it
Roof algae is removed chemically, not mechanically. We soft wash — low pressure, no more force than a garden hose, with a cleaning solution that kills the organism at the root rather than just rinsing the surface.
Every job starts with a full pre-soak of surrounding landscaping and ends with a post-soak rinse. Gutters, downspouts and hardscape get flushed as we go. Nobody walks the roof more than the job requires.
The colony dies on contact and weathers off over the following rains. Results hold for years, not months, because the organism is dead rather than displaced.
Questions we get about this
Will the black streaks come back after cleaning?
Is soft washing safe for shingles and tile?
Will the cleaning solution kill my plants?
Can you clean the roof without me being home?
Related: Soft washing explained · Outside house washing · all FAQs