The black streaks running down your roof aren’t dirt. They’re algae. Specifically, Gloeocapsa magma, a hardy bacteria that lives on the limestone filler in asphalt shingles and spreads from north-facing slopes outward. Pressure-washing it off makes the problem worse. Roof cleaning done right uses a low-pressure soft wash that kills the algae and the moss without touching the shingles.
Here’s exactly what that process looks like, why it’s safe for your roof, and what to expect when a crew shows up.
What roof cleaning actually removes
Three things grow on a roof in southern New England:
- Algae (Gloeocapsa magma). Causes the dark streaks. Eats the limestone in shingles, which is why the streaks darken over years. Spreads through airborne spores.
- Moss. Holds moisture against the shingles, lifts them at the corners, shortens roof life. Common on shaded slopes.
- Lichen. Hardest to remove. A symbiosis of algae and fungus that anchors into the shingle granules. Looks like crusty patches.
None of these are dirt. You can’t power-wash them off and expect them to stay gone. The roots (or spores) need to be killed, not just rinsed.
The soft wash roof cleaning process, step by step
1. Inspection and prep
Before we touch the roof, we walk the property and look for things that need protecting: gutters full of leaves, downspouts that drain into landscaping, plants right against the foundation, painted surfaces under the eaves. We pre-wet the plants and run a tarp or rinse line where the runoff will land.
We also check the roof condition. Missing shingles, exposed nail heads, or cracked flashing get flagged before we start. Cleaning a roof that already has issues won’t fix the issues, and we’d rather know up front.
2. Apply the cleaning solution
From the ground (or a ladder for steeper roofs), we apply a sodium hypochlorite blend through a low-pressure soft wash system. The solution is mixed to the right working strength for the algae load. Heavier staining gets a higher concentration. Lighter staining gets a lower one. It’s not the same mix on every roof.
Pressure at the nozzle is under 100 PSI. That’s about the same as a garden hose with a thumb over the end. The shingles never see force.
3. Dwell time
The solution sits on the roof for 10 to 20 minutes. During this time, it’s killing the algae and breaking down the moss. You can usually see the dark streaks lightening within the first few minutes. Heavier staining keeps lightening over the next 24 to 48 hours after the job is done.
4. Rinse
A low-pressure rinse takes the dead algae and the solution off the roof and into the gutters. We rinse the gutters, downspouts, and any landscaping near the drip line. The plants we pre-wet get rinsed again.
5. Inspection and walkthrough
We do a final walk to make sure nothing was missed and to point out areas where the staining was heaviest. Some of those areas keep lightening for a day or two as the solution finishes working.
Why pressure washing a roof is a mistake
Asphalt shingles have a layer of mineral granules on the surface. Those granules are what give the shingle its color and what protects the asphalt underneath from UV. Pressure washing strips them off.
You can see it happen in real time: a shingle hit with 2,000 PSI of water sheds granules into the gutter like sand. The shingle still looks clean from the ground. But UV starts breaking down the exposed asphalt within weeks, and the roof loses years of life.
Most shingle manufacturers (GAF, CertainTeed, Owens Corning, IKO) explicitly state that pressure washing voids the warranty. Soft washing is the only method they endorse.
How much does roof cleaning cost?
Roof cleaning cost depends on three things: the size of the roof, how much algae and moss are on it, and how accessible the roof is. For most single-story homes in Hartford County, a soft wash roof cleaning falls between $400 and $800. Two-story homes and homes with complex roof geometry (multiple peaks, dormers, steep pitch) run higher because the work takes longer.
Compared to a roof replacement (which can run $10,000 to $30,000 for the same house), a cleaning every two to three years is the easy math.
How often should you clean a roof?
For most homes in Connecticut, every 2 to 3 years keeps streaks from coming back. Some factors push it more often:
- Heavy tree cover (shade plus dropped debris feed algae and moss)
- North-facing slopes get more growth than south-facing
- Near water or in low-lying humid spots
- Older roofs with more limestone exposure
If you’ve never had it done and the streaks are obvious from the street, it’s been long enough.
Common questions
Will the streaks come back right away?
No. The algae are killed, not just rinsed. Surface staining starts lightening immediately and continues for a couple of days. The roof typically stays clear for 2 to 3 years before regrowth is noticeable.
Is the runoff safe for my landscaping?
Yes, with proper technique. We pre-wet plants, dilute the runoff with rinse water, and avoid concentrating drainage in any one spot. Sodium hypochlorite breaks down to salt and water once it’s done working.
Can it be done in winter?
Not below freezing. The solution needs liquid water to work, and you don’t want runoff freezing on walkways. Wicked Clean schedules roof cleaning from April through November in Hartford County.
What about moss specifically?
Moss takes the same soft wash treatment, but the dead moss needs time (or a follow-up gentle sweep) to clear off. We don’t pull moss off by hand because that strips granules.
Do I need to be home?
Helpful but not required. We need access to an outdoor spigot and to the property. If you’re not home, we leave a detailed summary of what we did.
Get your roof cleaned the right way
Wicked Clean LLC specializes in soft wash roof cleaning across Hartford County, CT. We use the technique your shingle manufacturer endorses and the runoff plan that protects your landscaping. Call (860) 748-8655 or request a free quote and we’ll tell you what your roof needs.
