What the black streaks are
Black streaks on a roof are a colony of blue-green algae called Gloeocapsa magma. They run downward, look dark gray or black, and are worst on north- and shade-facing slopes. They are not dirt, soot, or normal aging. The algae is airborne and spreads from rooftop to rooftop. It feeds on the limestone filler in asphalt shingles and covers itself with a dark pigmented sheath, which is the streak you see. Humid Chicago summers let it thrive, and once it takes hold it grows year after year until the roof is treated.
Moss and lichen often follow. They root into the seams, lift shingle edges, and trap moisture.
What the streaks do to a roof
The algae eats the mineral granules and the filler that shield shingles from UV, so the shingles wear faster. Moisture trapped under lifted edges freezes and expands through a Chicago winter and cracks the shingle. Left alone, a few streaks become full coverage, the growth spreads to nearby roofs, and a roof that should last decades can fail years early.
The dark growth absorbs heat, which raises attic temperatures and summer cooling costs. The streaks cost curb appeal: a streaked roof can knock thousands off a home's appraised value and scare off buyers. The wash restores HOA compliance. The roof is one of the most expensive components of the home.
Why the roof is soft washed
High pressure on asphalt shingles strips the protective ceramic granules and exposes the asphalt, which shortens roof life. It can knock shingles off, and it forces water up under them, where it can leak into the decking and attic. Most shingle manufacturer warranties prohibit pressure washing, and high pressure voids them. The blast does not kill the algae. It only knocks the surface back, so the streaks return within months.
Shingle manufacturers and the Asphalt Roofing Manufacturers Association call for low-pressure chemical cleaning. Soft washing and pressure washing are different methods. The solution does the work at under 100 PSI.
Surfaces
- Asphalt shingle roofs
- Architectural shingles
- Flat and low-slope roofs
- Tile and slate roofs
- Cedar shake roofs
- Metal roofing
- Gutters and downspouts
How a roof soft wash is done
- Shingle condition, flashing, and gutters are checked. Plants, shrubs, and downspout beds are pre-soaked and covered, and landscaping is tarped. The cleaning solution is plant-sensitive, so runoff is accounted for before any of it goes on the roof.
- The roof is coated evenly with a biodegradable solution blended for the algae, moss, and lichen present: a carefully diluted mix of sodium hypochlorite and a surfactant, applied with low-pressure equipment.
- The solution dwells. It kills the algae, mold, and lichen at the root and breaks down the moss. Nothing is scrubbed.
- A soft, controlled rinse carries away the dead growth and grime and leaves every protective granule in place.
- Gutters, downspouts, siding, and landscaping are rinsed clear of residue, and the runoff is confirmed to have dispersed. Plants, the lawn, and the home are left unharmed. The wash is safe for pets.
- We review the finished roof with you and clean up the property. Stubborn stains often keep fading and rinsing away with rain in the weeks after treatment.
How often to soft wash a roof
Soft wash a roof only when algae streaks or moss appear. Every two to three years is typical in this climate, sooner on a heavily shaded roof or a north-facing slope that stays damp. Tree cover and roof slope change the interval. The roof then stays clean far longer than a pressure rinse.
After the wash, zinc or copper strips along the ridge let trace metal ions wash down in the rain and inhibit algae. Trimming overhanging branches lets more sunlight dry the roof. Gutters that drain keep water from pooling. For siding, concrete, and wood, see how often to wash a house.
Where roof soft washing is available
Ernest Power soft washes roofs across Chicago and the greater Chicagoland area, including DuPage, Kane, and McHenry counties, and McHenry. Towns:
- Chicago
- Naperville
- Wheaton
- Hinsdale
- Oak Park
- Downers Grove
- Glen Ellyn
- Lombard
- Elmhurst
- Schaumburg
Don't see your area? Call — we may still be able to help.
Get a quote
The roof inspection and quote are free and have no obligation. Call (630) 403-0027 or email hello@ernestpower.com. The office is at 1429 Diehl Rd, Suite 200, Naperville, IL 60563. Hours are Monday to Friday, 7 am to 9 pm, and Saturday and Sunday, 7 am to 5 pm.
Send the property details from the contact page. House siding, driveways, decks, fences, and commercial washing are separate services.