Why We Use a Stronger Mix for Roof Washing — Our Soft Wash Roof Process

If your roof has dark streaks running down the shingles, the common assumption is that it's just dirt or weathering. It's not — and treating it as dirt is why so many roof-cleaning attempts either fail to work or actively damage the roof. What you're looking at is a cyanobacteria called Gloeocapsa magma, and cleaning it correctly requires a specific approach that's fundamentally different from how you'd clean a driveway or a house exterior.

What Those Black Streaks Actually Are

Gloeocapsa magmais a photosynthetic bacteria that feeds on the limestone filler in asphalt shingles. It travels by wind and bird activity, which is why you'll often see it spread from one roof to the next in a neighborhood over time. The dark color comes from the bacteria's UV-protective pigmented sheath — it's essentially the organism shielding itself from the sun.

Left untreated, Gloeocapsa magma retains moisture against the shingle surface, which accelerates granule loss and shortens the lifespan of the roof. Algae also attracts other organisms — once the bacteria take hold, moss and lichen often follow, especially on north-facing slopes with less sun exposure.

Why High-Pressure Washing Destroys Roofs

High-pressure washing is the wrong tool for asphalt shingles — full stop. Asphalt shingles are coated with mineral granules that protect the shingle from UV degradation and weathering. High-pressure water blasts these granules off the shingle surface. Once the granules go, the shingle's lifespan drops dramatically and the roof loses its ability to shed water properly.

Beyond granule loss, high pressure can crack or lift shingles, force water under flashings, and in worst cases void the shingle manufacturer's warranty. We never use high pressure on asphalt or tile roofs.

Our Mix: 3–4% Sodium Hypochlorite

For roof washing, we use a sodium hypochlorite solution at 3–4% concentration — significantly stronger than the 1–2% we use on house siding. There are two reasons for this:

First, roofs tend to have more established, deeply embedded organic growth than vertical siding surfaces. The algae and associated organisms have been growing for years in many cases, and a gentler solution may not fully penetrate and kill the root structure.

Second, roof surfaces are more porous than smooth vinyl or painted siding. A diluted solution absorbs into the shingle material before it can dwell long enough to be effective. A higher concentration ensures adequate active chemistry reaches the organism regardless of how porous the surface is.

The key point: higher concentration does not mean higher pressure. We still apply the roof wash solution at low pressure — under 100 PSI — using a dedicated soft wash pump and wide-angle low-pressure nozzles. The chemistry does the work, not the force.

The Application and Dwell Process

We apply the solution from the peak down, ensuring even coverage across the entire roof surface. The solution is allowed to dwell for 10–20 minutes depending on the severity of the growth. During this time, the SH oxidizes the bacteria and begins to break down the organic matter.

After dwell time, we rinse at low pressure from the peak down. On a good soft wash, you'll see the dark streaks and green growth visibly brightening as the solution works, and the rinse carries the dead organic matter off the roof and into the gutter system.

Moss and Lichen: A Harder Case

Moss and lichen are more stubborn than algae. Moss has a root-like structure called rhizoids that can penetrate the shingle surface. Lichen is a symbiotic organism (algae + fungus) with an even tighter bond to the surface.

Our 3–4% SH solution kills both, but they don't always release immediately from the shingle. Dead moss and lichen typically detach and wash off with rainfall over the following weeks after treatment. Attempting to force them off with high pressure would damage the shingles — so patience is the correct approach. We may recommend a follow-up inspection if heavy lichen was present, but in most cases the rain handles the final removal naturally.

How Long Roof Washing Results Last

A professional soft wash in NC's climate typically keeps a roof clean for 2–4 years. Roofs in heavy shade or in areas with overhanging trees and poor airflow tend to see regrowth faster. Roofs with good sun exposure on the primary faces often stay clean longer.

We offer annual maintenance plans that include periodic roof inspections and retreatment to catch growth before it re-establishes — which is particularly useful for properties with heavy tree cover.