Black streaks are pretty common on asphalt or Spanish tile roofs, especially when you live in a humid climate (like Florida). As a homeowner, you may have wondered, “How do I remove black streaks from my roof?”. There are several reasons black streaks can appear. By having your roof professionally cleaned as part of your routine home maintenance you increase the lifespan of your roof. Early detection of problems that result in black streaks early can save you hundreds or thousands in roof repair costs not to mention, maintaining a clean roof boosts “curb appeal”.

So what exactly causes black streaks on roofs?

Roofing specialists agree that black streaks are caused by an algae known as “gloeocapsa magma“.
Algae can easily be mistaken for soot, dirt, or tree debris. Most of these types of algae typically produce only localized discoloration. Dark streaks, or roof discoloration caused by algae, happens when built up deposits of algae begin to decompose turning from blue-green to black.

Humid areas of the country are most susceptible to dark streaks from algae. The areas of your roof that receive the least sunlight exposure ( typically, Northern Exposure ) are more likely to stay moist and encourage algae growth.

How do you remove black streaks from your roof?

There are several commercial products that remove algae stains, or you can mix up an effective solution at home. Here’s what you’ll need:

Bleach, water and trisodium phosphate (TSP) or similar commercial cleaner
Large Pump sprayer
Garden hose
Ladder ( that easily reaches the rof )
Plastic sheeting
Rubber soled shoes
Safety goggles 
Rubber gloves

Cover the plants around the perimeter of your home to protect them from bleach or chemical solutions. Ideally, you want to clean your roof on a cloudy day so sunlight doesn’t cause your cleaning solution to evaporate too quickly.

Step 1:

Create a solution of one part bleach, three parts water and three tablespoons of TSP ( Trisodium Phosphate ). Mix thoroughly and pour it in your pump sprayer.

Step 2:

Secure a firm footing for your ladder, ensuring to place it on firm, even ground, and carefully ascend to your roof. Note: It’s always best to leave roofs with a steep pitch to the professional roof cleaners that have equipment like bucket trucks. Carefully, climb to the top of the roof so you aren’t walking on wet shingles.

Pro tip: pay attention to the direction of the wind in order to prevent solution “sprayback”.

Step 3:

Soak the shingles with your solution and allow it to remain for at least 15 minutes, afterwards, rinse it off with your garden hose. If black streaks are still visible on the surface, repeat the process until they are all removed. Pressure washing removes the protective granules from your shingles. Do not use a pressure washer or highly acidic chemicals.

Roof work is dangerous. If you’re like many of the safety conscious families in Pinellas County, we recommend giving us a call, here at Apple Roof Cleaning.
With decades of experience, we ensure the best solution for your roof type. We always protect landscaping and pets from runoff of non-toxic chemicals.

If you have questions about the care of your roof, contact one of our 5-star rated roof cleaning experts today.