Services / Roof cleaning
Roof soft washing and algae removal
The black streaks on a Northern Virginia roof are Gloeocapsa magma algae, not dirt. It comes off with a low-pressure soft wash — never a pressure washer, which strips the granules that protect the shingle and shortens roof life.
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Those dark streaks running down the north-facing slope are not dirt and they will not wash off in rain. Left untreated the algae holds moisture against the shingle and accelerates granule loss.
Signs you need roof cleaning
- Black or dark green streaks running down the roof, usually starting on the north-facing slope
- Green, fuzzy patches, especially near valleys or chimneys where moisture collects
- Moss building up along shaded edges or under overhanging branches
- Granules collecting in gutters, which can mean algae has already started degrading the shingle
- It has been three or more years since the roof was last cleaned
What is included
- Soft wash only — no pressure on shingles, ever
- Asphalt shingle, cedar shake, tile, and metal roofs
- Landscaping pre-wet and rinsed to protect plantings
- Results typically hold three to five years
- Gutter brightening available at the same visit
How it works
- 1 Inspect the roof from the ground and identify shingle type, slope, and growth pattern
- 2 Pre-wet and cover surrounding landscaping
- 3 Apply the soft-wash cleaning solution to the affected areas
- 4 Let the solution dwell to kill algae, moss, and lichen at the root
- 5 Low-pressure rinse from the ground or a ladder — no pressure washer, no walking the roof deck
Understanding the problem
What is actually happening — and why the method matters
Gloeocapsa magma is a blue-green algae, technically a cyanobacteria, that travels by airborne spore and lands on roofs across the humid mid-Atlantic. It feeds specifically on the limestone filler used in asphalt shingles for weight and fire resistance, which is why it is so common on asphalt roofs and far rarer on metal or slate. The streaks look black because the algae grows a dark protective coating against UV light, not because it is soot or dirt — which is also why rinsing with plain water barely touches it.
Pressure damages a roof for a specific reason: asphalt shingles are topped with a layer of ceramic-coated granules that shield the asphalt underneath from UV exposure. A pressure washer aimed at close range strips those granules off. Once they are gone, the exposed asphalt degrades in sunlight far faster than normal wear — which is why most shingle manufacturers explicitly exclude pressure-washing damage from their warranties.
A soft wash avoids all of that by using chemistry instead of force. The cleaning solution is applied from the ground or a ladder with a low-pressure sprayer, dwells long enough to kill the algae, moss, and lichen at the root, and is rinsed with no meaningful pressure at all. Because the growth dies rather than getting blasted off, a freshly soft-washed roof often looks slightly streaky for a few days afterward — normal rain finishes rinsing the dead algae away over the following days to weeks.
Common questions
Questions about roof cleaning
Does roof cleaning damage shingles?
Soft washing does not. Pressure washing does — it strips the granules that protect the shingle. We never put pressure on a roof.
What are the black streaks on my roof?
Almost always Gloeocapsa magma, a blue-green algae that feeds on the limestone filler in asphalt shingles. It is extremely common in our humid summers.
How long do results last?
Typically three to five years in this climate, depending on tree cover and which direction the slope faces.
How much does roof cleaning cost?
Cost depends on roof size, pitch, and how much algae has built up. We provide a free written quote — often far less than the cost of a premature roof replacement, which is what unchecked algae eventually forces.
Do you need to walk on my roof to clean it?
Rarely. Most roof cleaning is done from a ladder or the ground with an extension wand, which is safer for the crew and for the shingles than walking the roof deck.
Will my roof look perfectly clean the same day?
Not always immediately. Soft washing kills the algae and growth at the root, but full rinse-off from rain can take a few days to a couple weeks. This is normal and expected.
Can roof cleaning extend the life of my shingles?
Yes. Algae and moss trap moisture against the shingle and accelerate granule loss. Removing that buildup slows the wear that eventually leads to premature replacement.
Do you clean gutters at the same time?
Gutter brightening is available at the same visit — it is a natural add-on since we are already on a ladder working the roofline.
Is soft washing safe for solar panels near the roofline?
We avoid direct contact with solar panels during a roof soft wash and can quote solar panel cleaning as a separate, panel-safe service if needed.
Will pressure washing void my shingle warranty?
Most major shingle manufacturers explicitly exclude pressure-washing damage from their warranties. Soft washing does not carry that risk, which is part of why we never use pressure on a roof.
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