5 Tips For Dealing With Roof Algae

Slick black stains on your asphalt-shingled roof may at first make you nervous. Is it mold, soot, or a sign of something more sinister? The actual culprit is algae. Although the conditions that lead to the algae can eventually damage your roof, its ugly appearance is usually a more immediate concern. The following tips can help you remove the algae and prevent it from coming back.

Tip #1: Both Kill and Remove the Algae

There are many roof cleaners available. Most of them use chlorine bleach or trisodium phosphate (TSP), or a combination of the two. This is because these two ingredients both kill algae and remove the black stains. You can use a premixed cleaner or you can dilute TSP or bleach in water to make your own cleaner. Just remember that both chemicals can cause burns and irritation, so wear gloves and eye protection. Also, cover landscape plants with a tarp to protect them from any run-off.

Tip #2: Wait for an Overcast Day

Your roof heats up when the sun is shining, which can cause any cleaning solution to evaporate off before it has time to work. Wait for a cloudy, dry day and then soak the shingles with the cleaning solution of choice. It's best to work from the ground or the top of a ladder (with someone below to help hold it) and to use a pump sprayer to soak the roof. Walking on your roof can result in damage.

Tip #3: Soak and Then Rinse

It takes both TSP and bleach some time to work. Let the cleaner sit on the shingles for 15 to 20 minutes, or as advised on the label if you are using a commercial roof cleaner. Ignore the temptation to scrub the roof—this will just result in damaged asphalt shingles. After the allotted time, rinse off the roof with a garden hose or a pressure washer set to a low setting.

Tip #4: Tackle the Root Cause

Chances are your algae problems are happening on the shady portion of your roof. This is because shade results in slow evaporation and damper conditions, which the algae needs to grow. Eventually this dampness can also weaken your roof. You can trim back overhanging trees to help allow more light and wind in so the roof dries out more quickly. This only works, of course, if sun can even reach this section of the roof. If the area is blocked from sunlight, such as on the north side of your home, you may need to take further steps.

Tip #5: Put In Metal Strips

Zinc roof strips are typically applied near the peak of the roof. Algae can't grow in the presence of the zinc. Each time it rains or the roof gets wet, a small amount of zinc leaches down the shingles and makes them an algae-free zone. If you get fresh strips installed each time you replace your roof, you will never need to worry about algae again.

For further questions about your roofing needs, contact your local roofer.