If you have nasty black stains on your asphalt shingle roof, don't worry.  The black staining won't damage the shingles, and it won't make your roof leak.  This black staining is typically caused by an algae, and usually shows up on areas of the roof that don't get much sunlight, such as the north side.

Black roof stains 

Garden Sprayer

If you don't like the look of these stains, you can clean your roof with some basic supplies that you probably already have at home.  Simply mix up a solution of two parts water to one part bleach in a garden sprayer.  Spray down the affected areas of your roof with this solution, let the solution soak for about ten minutes, and then  spray the cleaning solution off your roof with a garden hose.

For this blog, I started by cleaning a small section of the roof and letting the shingles dry, just to get a good photo showing how effective this is.

Black roof stains cleaned

A few precautions:

  • Protect your lungs.  Bleach is nasty stuff, and you'll get it in the air when you spray it with the garden sprayer.  Wear a respirator.
  • Watch where you spray the cleaning solution.  The solution won't harm your shingles, but you could certainly do damage to other surfaces or people if you're not careful.
  • Wear grubby clothes.  If you get this solution on your clothes, you'll ruin 'em.
  • Protect your vegetation.  If the cleaning solution will run off the roof on to your plants, you should cover them up with tarps or something similar.
  • Be careful on a ladder, and don't walk on the roof.  This is 'no-duh' advice, but I'm saying it anyways.  Even if you're used to walking on your roof, it will get very slippery once the bleach interacts with the algae, and you could easily slide off the roof.
Some people get whipped up over the topic of bleach.  If you don't like the idea of using bleach, you could buy a product made for cleaning roofs, such as RoofOX 3000.  I've heard good reviews, but never tried this stuff personally.
 
Reuben Saltzman, Structure Tech Home Inspections - EmailMinnesota Home Inspections
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