Those unsightly black streaks on Florida roofs aren't dirt—they're algae called Gloeocapsa magma. Combined with Florida's humidity, mold and mildew growth is also common. Here's how to safely clean your roof and prevent regrowth.
Understanding Roof Algae and Mold
Algae (Black Streaks)
- Appearance: Dark streaks, usually on north-facing slopes
- Cause: Gloeocapsa magma feeding on limestone in shingles
- Spread: Airborne spores spread from roof to roof
- Damage: Primarily cosmetic, but can shorten shingle life
Mold and Mildew
- Appearance: Green, black, or white patches
- Cause: High humidity, shade, organic debris
- Damage: Can deteriorate roofing materials over time
- Health: Can affect air quality if it enters home
Moss
- Appearance: Thick green growth, usually in shaded areas
- Cause: Excessive moisture, lack of sunlight
- Damage: Can lift shingles and trap moisture
- More common: On north-facing slopes in Florida
Safe Cleaning Methods
The Right Approach: Soft Washing
Soft washing uses low pressure with cleaning solutions:
- Won't damage shingles or tiles
- Kills algae, mold, and mildew at the root
- Results last longer than pressure washing
- Recommended by roofing manufacturers
DIY Cleaning Solution
For light algae growth:
- Mix: 50% water, 50% household bleach (sodium hypochlorite)
- Alternative: Commercial roof cleaning products
- Never use: Pressure washer at high settings
Severe Algae or Mold Problem?
Professional cleaning protects your roof while getting it sparkling clean.
Get Cleaning QuoteDIY Roof Cleaning Steps
Safety First
- Never clean a roof alone
- Use proper safety equipment (harness, non-slip shoes)
- Avoid cleaning in direct sun (solution evaporates too fast)
- Protect landscaping below
- Be extremely careful on wet surfaces
- Consider: Is it worth the risk? Professional cleaning is affordable.
Step-by-Step Process
- Protect plants: Wet landscaping and cover with plastic sheeting
- Wet the roof: Pre-soak with plain water
- Apply solution: Use pump sprayer to apply cleaning solution
- Let it work: Allow 15-20 minutes dwell time
- Rinse gently: Use garden hose (low pressure only)
- Rinse plants: Thoroughly rinse all landscaping
- Repeat if needed: Heavy staining may need second application
Important Warnings
- NEVER pressure wash asphalt shingles—removes granules
- NEVER walk on tile roofs—tiles break easily
- Don't clean in rain or when rain is expected
- Bleach kills plants—protect landscaping thoroughly
- Cleaning doesn't fix underlying damage
Prevention Strategies
Zinc or Copper Strips
- Install strips along ridge line
- Rain washes metal ions down roof
- Creates environment algae can't thrive in
- Lasts 10-20 years
- Cost: $200-500 for typical installation
Algae-Resistant Shingles
- Contain copper granules that inhibit algae
- Best option when replacing roof
- Most major brands offer this option
- Small cost premium over standard shingles
Environmental Modifications
- Trim trees to allow more sunlight
- Improve air circulation around roof
- Clear debris that holds moisture
- Ensure proper attic ventilation
Professional Roof Cleaning
When to Hire a Pro
- Steep roof pitch (safety concern)
- Tile or slate roofing
- Heavy mold or moss growth
- Two-story or higher homes
- No proper safety equipment
- Not comfortable on roofs
What Professionals Do Differently
- Use commercial-grade solutions
- Have proper safety equipment
- Know correct pressure and technique
- Can identify underlying damage
- Often apply preventive treatment
Cost of Professional Cleaning
- Typical range: $300-700 for average home
- Factors: Size, pitch, severity, accessibility
- Often includes: Gutter cleaning
- Add-ons: Preventive treatment $100-200
Frequency of Cleaning
Recommended Schedule
- With prevention measures: Every 3-5 years
- Without prevention: Every 1-2 years
- Heavy shade/humidity: Annually
- Coastal areas: More frequent due to moisture
Common Mistakes to Avoid
- Using pressure washer on shingles
- Walking on tile roofs
- Using too-strong chemical concentrations
- Neglecting to protect landscaping
- Cleaning in direct afternoon sun
- Not addressing underlying moisture issues
- Thinking cleaning alone fixes damaged shingles
When Cleaning Isn't Enough
Sometimes cleaning reveals other issues:
- Shingles damaged beyond cosmetic cleaning
- Granule loss indicating aging
- Moss has lifted shingles
- Mold indicates water intrusion
- Repeated rapid regrowth
If cleaning reveals these issues, contact a roofing professional for assessment.
Need roof cleaning or have concerns about what you're seeing? Contact SkyGuard Roofing at (754) 946-4344 for professional advice.
