Why Do Roof Stains Show Up in the First Place?
If you live in a humid area like Tennessee, you’ve probably seen those dark streaks that run down asphalt shingle roofs. That’s generally a type of algae called “Gloeocapsa magma”. It feeds on the limestone filler in your asphalt shingles. Gradually, it spreads and makes your entire roof look old and worn out.
Lichen and moss are also common, especially on tile roofs or shaded areas, as they hold moisture and can break down your shingles faster. The longer you leave them, the worse they get, so start cleaning sooner rather than later.
What is Needed Before Starting Cleaning Roofs
No fancy setup is needed to tackle roof stains. Here’s what most pros recommend:
- A garden sprayer to apply your cleaning solution
- A roof cleaning product
- A garden hose with a strong spray nozzle
- Safety gear (non-slip shoes, gloves, and eye protection)
A pressure washer is sometimes used, or the soft washing method is used, depending on the professional you hire. They will clean depending on the type of stain and type of surface, so make sure that you are hiring your local professional for this job, so that the job is done properly and also safely.
Choosing the Right Cleaning Solution for Roof Cleaning
When figuring out how to clean roof stains, what professionals use matters as much as how they use it.
If you are doing it yourself, which is not recommended, you can mix sodium hypochlorite (liquid chlorine bleach) with water for cleaning roofs. This mix is strong enough to kill algae but gentle enough not to harm your roof shingles. Some also add sodium laurel sulfate, a surfactant that helps the spray stick to the roof longer. But it would be best to leave it to the professionals you are hiring.
Professional-grade cleaners often contain sodium hydroxide. This product, called a roof detergent, works best for breaking down tough stains. Remember that too much sodium hydroxide can discolor shingles or nearby landscaping.
How Professionals Clean Roof Stains — Step-by-Step
Quick overview: Pros almost always use soft-washing, a chemical clean with low pressure, instead of high-pressure washing. This kills algae and moss at the root without stripping shingle granules or voiding warranties.
1. Pre-job Inspection & Prep
- Inspect the type and age of your roof, as well as the manufacturer’s warranty. Note any fragile areas, including vents, skylights, and solar panels.
- Professionals check the weather (cool, overcast, and no rain for a few hours), locate the hose access, and determine where the runoff will go.
- Protect outdoor furniture, HVAC intakes, and landscaping — pros cover or lightly water down plants and may lay tarps where runoff collects.
- They then put on safety gear, including harnesses, ladder stabilizers, roof anchors, and non-slip boots.
(This step prevents damage and environmental problems before a drop of chemical is mixed.)
2. Clear Loose Debris & Pre-rinse
- Remove loose debris, leaves, and sticks by hand or with a leaf blower.
- Lightly rinse to remove dust and to pre-wet the surface; this helps the chemical dwell evenly and removes loose soil first.
3. Mix the Professional Cleaning Solution (What Pros Use)
- Professionals commonly use a sodium-hypochlorite (bleach)-based soft-wash solution and a bleach-stable surfactant (e.g., lauramine/myristamine oxide blends). These surfactants help the solution cling to and penetrate the biological stains.
- Concentrations and exact recipes vary by local rules, surface, and product label — experts follow the product/EPA label, as well as the roof manufacturer’s cleaning guidance, rather than guessing.
- Important safety note: never mix bleach with acidic products or ammonia (this creates toxic chlorine gas). Use only chemicals that are designed to be mixed together and follow the label’s PPE instructions.
4. Apply the Solution With a Soft-wash System (How Pros Apply)
- Professionals generally use a low-pressure pump/soft-wash rig or a commercial downstream injector and a pump resistant to hypochlorite. This creates an even spray and prevents physical damage.
- Application pattern depends on roof access and slope. Some pros spray from the bottom up to reduce streaking and avoid run-off reloading treated areas, while others work top-to-bottom to control flow. The choice depends on your roof’s shape, wind, and access. The main point is to apply evenly and work in manageable sections so the solution dwells properly.
5. Let the Chemistry Do the Work
- Soft washing experts let the solution sit for 10 to 20 minutes, long enough to kill algae and moss but not so long that it dries out. During this time, the surfactant keeps the solution on the roof while the hypochlorite kills the organisms. They do not let the chemical dry on the roof.
6. Low-pressure Rinse (if Required)
- Rinse with a low-pressure pump or garden hose from top to bottom to flush residues away, or use the pro’s chosen method to control run-off. Do not use a high-pressure nozzle that can strip shingle granules, as this voids warranties and shortens the roof’s life.
7. Re-inspect & Spot-treat
- Professionals then inspect for stubborn patches and will reapply the solution only where needed or use a soft brush on small spots (never aggressive scrubbing that scrapes granules). Repeat and rinse on those spots until satisfied.
8. Post-job Cleanup & Prevention
- Rinse down plants and surfaces affected by run-off. Avoid phosphate-heavy detergents like TSP where possible; older formulas used TSP, but it raises environmental concerns. Professionals now prefer phosphate-free alternatives and follow local disposal rules.
When to Use a Pressure Washer for Roof Cleaning
You might hear about contractors who pressure-wash tile roofs. On hard surfaces like concrete or clay, a pressure washer can be used carefully to blast away heavy moss or dirt. But for an asphalt shingle roof, stick to low-pressure or soft-wash methods. This keeps your shingles intact and avoids early wear.
Tips for Keeping Roof Stains Away Longer
Once you’ve got your roof looking fresh, you want it to stay that way. You can:
- Trim overhanging branches to let the roof dry faster after rain.
- Install copper or zinc strips near the ridge. When it rains, they release ions that make it harder for algae to grow on roof shingles.
- Do a light rinse every year with a diluted cleaning solution using your garden hose.
This upkeep makes cleaning roofs quicker next time.
Bringing It All Together
Cleaning roof stains is about applying a good solution with a garden sprayer, using the right product, and rinsing gently with a garden hose. Skip harsh pressure washing on asphalt shingles and stick with low-pressure methods.
When dealing with green algae stains, black streaks, or dirt on tile roofs, a little time spent cleaning can make a big difference in how your home looks. By hiring your local roof cleaning company every few months, your shingle roof can look like new, and you’ll be proud every time you pull into the driveway.
Professional Roof Cleaning Services in Tennessee
If you’ve noticed black streaks or dark algae stains on your roof, it’s time to call Blueline Pressure Washing. Why trust us? We’ve served the Tennessee community for years and earned over 425 five-star reviews on Google & Facebook. We back our work with a 100% Satisfaction Guarantee and even offer a Military & First Responder Discount as a thank-you.
Blueline Pressure Washing does more than roof cleaning. We also handle pressure washing, gutter cleaning, Christmas light installation, power washing, wood restoration, and more.
Serving Jonesborough, Colonial Heights, Kingsport, Bristol, Johnson City, and surrounding areas, we’ll bring your roof back to life. Call today for a quote and see how we can make your roof look new again.
