If you’re seeing strange black streaks on your roof shingles, you’ll be glad to know it isn’t necessarily a sign of expensive roof repairs in your future. You’ll also be glad to know that it’s not mold! “Roof mold”, as it’s commonly called, is actually a particular type of blue-green algae.
You might notice that the algae is growing mostly on the North side of your home. This is because that side of your roof doesn’t get nearly as much sun, which would dry up the algae naturally. Instead, this section of your roof stays damp and partially shaded all day— the perfect conditions for scum to spread.
Regardless of what it actually is and why it’s there, the problem is that it’s ugly and it can actually lead to more serious (and costly) roof problems. So before the moisture starts working its way beneath the shingles and into the structure of your roof, follow these steps and nip this thing in the bud.
You’ll need to spray the affected area with a Zinc Sulfate chemical solution. You can make your own solution from 5 parts water and one part Zinc powder. You could also head down to your home improvement store and take your pick from the variety of products designed to handle this task, but this option is far more expensive.
*Do not, and I repeat, do not use a pressure washer to clean your roof. The powerful spray can detach protective granules and damage and/or loosen your shingles.*
If you’re using a zinc mixture, make sure you wet any plants near the foundation of your home prior to spraying your roof so that the runoff doesn’t damage them. If you have lots of plantings surrounding your home, consider using a cleaner made with natural ingredients.
Your chemical solution should also work to kill any mosses and lichens that have built up on your roof. You’ll know they’re dead when they turn white, right before your eyes. But, they won’t wash away like the algae will, so to remove the moss you’ll have two options. You can either brush them off yourself (a broom works well), or you can just wait for the rain to remove them for you. The former may not be as easy, but you wont have the moss clogging up your gutters.
Once your roof is clean again there are things you can do to prevent the algae and other fungi from returning. Re-applying zinc annually means you’ll never have to clean the surface again. Although, we do not suggest you use zinc strips. They tend to be short lived and don’t stay in place very well. The oxide is thin and too weak to be effective in the Northwest.
Also, refrain from using bleach on your roof. It is hard on both asphalt shingles (makes them brittle over time) and metal gutters (will chalk the coating). Bleach is not environmentally friendly either.
Discovering what looks like mold on your roof shingles can have you expecting the worst, but in reality it’s an easy fix and you can prevent it from happening again.
If you need help tackling any fungus on your roof, call us at 503-635-8706.