Black Streaking on your Roof and Potential Mold Growth

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Black Streaking on your Roof and Potential Mold Growth

The black streaks on your roof shingles is usually not mold, however it can be an indication that you may have possible mold growth in your attic. Black streaks generally come from deteriorating roof shingles and defects with roofing. The black spots or streaks is actually more than likely an algae called Gloecapsa Magma. Algae travels through the air similar to mold, therefore if one neighbor receives a few spores, the rest of the neighborhood may soon have a black streaking problem on their roof as well.

When a home has black streaks on their roof this can be an indicator that there is mold growth in their attic. This can become a serious issue seeing as it is destructive and will eat away at the plywood, joists and rafters. If there is mold growth in the attic then it means that there is also a ventilation issue.  

In the summer, improper ventilation can cause attic heat to reach 160˚F. This can lead to cracking, warping & the breakdown of wood framing. Premature aging of your roofing system, such as curling of the roof shingles, damage to siding, exterior & interior paint and wallpaper. Believe it or not, a roof shingle warranty can be voided if it’s discovered you don’t have the proper ventilation.

Industry standards say that for every 150 square feet of heated ceiling space, you need one square foot of ventilation between the soffit vents and either a ridge vent or box vents on the outtake. In the winter time, warm air will migrate to the attic. When it mixes with the cold plywood surfaces, it forms condensation. If the condensation sits on the plywood for too long, it will start to form mold growth on the plywood and supports. With the proper air flow in the attic, it will keep the plywood dry and free from moisture and mold growth. Remember; more ventilation is always better than not enough. Be sure your soffit vents are not blocked by your attic insulation. This will prevent proper air flow. You may also want to check your bath fan venting. Is it run up and out of your roof or did the installer simply and improperly vent it directly into the attic? (This happens much too frequently.) If it is incorrect, call a mold remediator to not only rectify this but also to check your attic for possible mold growth.

If you have black streaking on your roof then you should take a peak in your attic for any signs of mold growth. If you are able to catch the problem sooner rather than later in your attic, it will save you time and money. If you notice any signs of mold growth in your attic, make sure to contact a mold professional to come out to do an inspection. For more information please visit Comprehensive Mold Management at

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