What Are The Black Streaks On My Roof?

Date Posted:

May 1, 2024

Author:

Daryl Gentry

If you have an older roof, you will eventually start to notice signs of wear and tear.

Your roof will continually brave the elements, so it's only natural for it to show some signs of its age.

Regular roof inspections performed by you or your local roofing company will help put your mind at ease.

Inspections will let you know if an issue on your roof is purely cosmetic or if there's an actual problem that needs to be addressed.

A common eyesore many homeowners complain about on their older roof are black streaks.

These dark streaks on your shingles don't mean you need to panic and replace your roof.

But, what are these black streaks, and what can we do about them?

We'll take a look at that question and more in the article below.

The black streaks you've noticed on your shingles are actually algae growth.

It's an algae called Gloeocapsa magma.

These blue-green algae accumulate and develop a dark, hardened outer coating, causing the eye-soar on your roof.

The algae can worsen and become more noticeable year by year.

They can also trap moisture and cause premature shingle aging and granule loss.

If you want to avoid algae growth on your roof, you can install an algae-resistant shingle.

If the streaks don't bother you much, or you don't want to invest in a new roof, you can install zinc or copper strips along the top course of shingles.

When it rains and water hits the strips, they will produce a solution that will run down the roof and keep the algae from growing.

They just won't eliminate any existing black stains.

Why Do Shingles Get Algae?

Algae spores are airborne and are carried by wind, animals and can even be carried on your clothing.

Because they are airborne, they can quickly spread from roof to roof in a neighborhood or from townhouse to townhouse or apartment to apartment.

If it seems like asphalt shingle roofs are getting more black streaks today than twenty or so years ago, it's because they are.

Traditionally, asphalt shingles were made of asphalt.

To save money, today's asphalt shingles still contain asphalt, but they are mostly made up of fillers like fiberglass and crushed limestone.

These materials encourage the growth of algae.

The algae use the crushed limestone filler as their primary food source.

Are The Black Streaks On Roofs Harmful?

Whether or not the black streaks on an asphalt roof are harmful depends on who you ask.

Some roofing professionals say that constantly cleaning a shingled roof with chemicals like oxygen bleach will deteriorate the roof faster than the algae itself.

Other roof experts say that the black streaks on roofs will eat away at the shingle's base, causing the shingle to expand and contract with temperature changes.

The constant movement can shorten the life of your roof.

Some homeowners and condo associations require roof algae removal regularly, no matter what the experts say.

How To Get Rid Of The Black Stains

Everyone will admit that black roof streaks are an eyesore.

So, what's the best way to get rid of these unsightly black roof stains other than a complete roof replacement?

Fortunately, several available products can remove black stains from asphalt shingle roofing.

Or, if you're the DIY type, you can make your own.

All you need is:

Bleach, water, and trisodium phosphate, or a commercial cleaner
A pump sprayer
A garden hose
A ladder
Plastic sheeting
Non-slip shoes
Safety goggles and rubber gloves

If you have any plants around the perimeter of your home, make sure they are covered to avoid spraying them with any chemicals.

If possible, clean your roof on a cloudy day so sunlight doesn't cause your cleaning solution to evaporate too quickly.

Mix your solution of one part bleach, three parts water, and three tablespoons of TSP and pour it in your pump sprayer.

Use your ladder to carefully climb to the top so you aren't walking on wet shingles and the solution doesn't blow back in your face.

Soak your shingles with your homemade cleaning solution and allow it to sit for at least 15 minutes and rinse it off with your garden hose.

If any types of roof algae remain, repeat the treatment until they are gone.

If you aren't comfortable doing this, contact a roofing professional for help.

Hire a Professional to Clean Your Roof

Contact your local roofing company if you aren't comfortable doing roofing repairs and don't want to climb on a slippery roof, or you're worried about voiding a warranty from your roofing manufacturer.

They can help keep your roof clean and get those ugly black algae stains off of your roof.

TK Roofing and Gutters can inspect your roof and use algae treatment products that are biodegradable and non-corrosive to clean your roof.

While they are up there, TK Roofing and Gutters can perform a complete roofing inspection to make sure you don't have any defective shingles.