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Why Are There Dark Streaks on Your Roof & How Do You Remove Them?

How do you remove stains from roof shinglesThere’s nothing worse than spending a huge amount of time and money on a gorgeous and long-lasting roof, only to come home one day and realize your lovely asphalt shingles are covered in ugly black streaks.

So what exactly are these streaks, and why did they show up on your roof all of a sudden? Apart from being unsightly, are they actually harmful? Is it possible to clean them on your own, or will you need the help of a professional roofing service in Mount Laurel, NJ, and other communities across New Jersey, Virginia, and Maryland?

We have previously listed a few time-tested roof maintenance tips and provided you with a step-by-step roof cleaning guide. Now we’ll explain why black streaks sometimes appear on roof shingles and how to effectively remove them. Keep reading to learn more.

What causes black streaks on shingles?

The dark stains or streaks that sometimes form on shingle roofs are usually a sign of a Gloeocapsa Magma infestation. This is a species of bacteria that resembles algae and thrives in damp and cold environments. It’s very likely to show up in humid climates, or on surfaces that receive plenty of dew or shade.

Since the north-facing side of a roof is normally the side that gets the least amount of sunlight, this is where the first streaks will usually appear. However, they can also occur in areas that have significant tree coverage. Since Gloeocapsa Magma spreads via air, there’s a significant possibility that it will soon infest the surrounding roofs as well.

On top of being an eyesore and reducing the curb appeal of your home (which in turn reduces its property value), this bacteria also absorbs and holds moisture. If left untreated, it can cause your shingles to age, rot, or lose their granules prematurely.

How do you remove stains from roof shingles?

Sometimes, simply washing your roof is enough to remove the bacteria. If this doesn’t work, however, you can get rid of those ugly black stains by following the steps below. Just remember to wear protection (goggles, rubber gloves, overalls, long sleeves) and to perform the cleaning on an overcast or cold day with minimal wind.

Do the following:

  • First, protect any vegetation, landscaping, and lawn furniture from overspray by covering it up and/or moving it elsewhere.
  • Get a cleaning chemical designed specifically for this type of roof cleaning, or make your own by mixing a cup of trisodium phosphate with a gallon of bleach and five gallons of water.
  • Put your cleaning solution in a pump-style garden sprayer and spray down every inch of the roof. 
  • Let the solution sit for 15-20 minutes or, if you’re using a commercially-produced cleaner, however long is recommended on the label. 
  • Rinse the roof with a garden hose. If necessary, do this multiple times until all of the residue from your cleaning solution is gone.

What causes black streaks on shinglesWhere can I hire an acclaimed roofing service in Mount Laurel, NJ, and throughout the mid-atlantic?

If you’re in need of an established home improvement company that can provide you with a broad selection of roofing, solar, window, door, siding, and gutter services, look no further than Nu Look Home Design.

We are an Owens CorningTM Platinum Preferred Contractor that boasts a satisfaction rate among customers of no less than 94%. We will happily attend to the needs of your home while you deal with your other responsibilities or relax at the Mount Laurel Community Center.

Our services are by no means limited to Mount Laurel, so don’t hesitate to contact us if you’re located elsewhere in New Jersey, Maryland, or Virginia.


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