What Are the Black Streaks on My Roof? (And How to Remove Them)

You have probably noticed the dark streaks running down your roof, usually worst on the shaded side. Most people assume it is dirt, or just the roof getting old. It is neither. Those streaks are a living algae, they are feeding on your shingles, and they will keep spreading until something is done about them. Here is exactly what it is and how it comes off safely.

The streaks are algae, and it is alive

The black staining on your roof is a type of algae. It is extremely common in humid climates like East Tennessee, and it settles onto roofs and spreads across the shingles. It shows up as dark streaks because it grows and flows downward with the rain. It is not a stain from age and it is not dirt that will rinse off. It is a living organism that has taken up residence on your roof.

Here is the part that should get your attention. The algae actually feeds on the material in your shingles. Left unchecked, it is not just ugly. It is slowly working on the surface that protects your home.

Those streaks are not dirt and not old age. They are living algae feeding on your shingles, and they only spread from here.

Why East Tennessee roofs get it so bad

Our climate is a perfect home for roof algae. Warm, humid air, plenty of shade from all the trees, and moisture that lingers give it everything it needs. Homes around Knoxville and Union County, especially ones tucked under tree cover, tend to get streaks faster and heavier. The north-facing and shaded sections almost always show it first, because that is where moisture sits the longest.

Why you cannot just blast it off

The instinct is to grab a pressure washer and blast the streaks away. Do not. A shingle roof must never be pressure washed. High pressure strips the protective granules off the shingles, shortens the life of the roof, and can void the manufacturer warranty. And because the algae is alive with roots in the surface, blasting it only knocks the top layer loose. It comes right back.

• ▸High pressure blasts off the granules that protect your shingles.
• ▸It can crack and lift shingles and force water underneath.
• ▸It can void your shingle warranty.
• ▸It does not kill the algae, so the streaks return.

How a soft wash removes it for good

The right way to remove roof algae is soft washing. We apply a cleaning solution at low pressure that kills the algae down to the root, let it work, and then gently rinse. Because the growth is killed rather than just knocked loose, the roof stays clean far longer. And because there is no high pressure and no scrubbing, the shingles and their granules are never damaged.

1. Apply the right solution at low pressure so the shingles are never harmed.
2. Let it kill the algae and any moss down to the root.
3. Gently rinse the roof clean.
4. Enjoy a roof that looks new and stays clean, with the warranty and granules intact.

What roof soft washing costs

A roof soft wash falls in a ballpark of roughly $300 to $700 depending on the size of the roof, the pitch, and how much algae and moss is present. That is a planning range. The exact price comes from a free estimate where we can see the roof.

Do not wait until it takes over

Roof algae only spreads. A few light streaks now become a fully darkened roof in a few years, and once moss joins in, it holds moisture against the shingles and makes things worse. Catching it early keeps the job smaller and protects the roof. If you are seeing streaks, it is already established, so the sooner it is handled, the better.

About Can Do Pressure Washing

Can Do Pressure Washing LLC is a locally owned company based in Maynardville, run by Cody, serving Knoxville, Maynardville, Tazewell, and the East Tennessee area. We soft wash roofs the safe way, never with damaging high pressure, so those black streaks come off and stay off, for homes and businesses alike. Free estimates, same-day service, satisfaction guaranteed, and we are reachable 24/7.