What Are the Dark Streaks on My Roof?

Have you ever noticed dark stains, marks, or discoloration on your roof? If so, you are experiencing a buildup of algae and lichen.

What are Algae and Lichen?

Most of us know algae as the green stuff that covers the top of a dying lake. It's sometimes considered a plant but is most commonly classified as a protozoan. It spreads and grows when spores are released into the air and land on a roof or object. They need moist conditions to survive, hence the roof being a common spot.

Lichen, on the other hand, is the reproduction of a fungus and an alga. On a roof, it is formed when algae or fungus that are already present create a symbiotic relationship with each other. Typically, algae and fungus end up on your roof from wind debris or nearby trees.

Why Is It on My Roof?

The short answer is because it provides the perfect wet environment to live in.

The longer answer regards how shingles have been made in the past. Typically, roofs with dark spots of discoloration are likely older than 15 years. Back then, manufacturers of shingles were not aware of the features that could be added to their products to discourage and prohibit the growth of algae and lichen. 

Today, shingles are made with zinc and copper granules mixed into the color granules. These elements are known to kill off all the little organisms that grow into algae and lichen.

How Can I Combat Algae and Lichen on My Roof?

The most obvious answer is to look into replacing your roof. When you do this, you will be fitted with a more modern shingle, one that has zinc and copper built into it. There are other alternatives, like manually cleaning it with a simple solution; however, you run the risk of it growing back. 

Some people decide to install zinc or copper strips on their roof, which can be installed on a new or existing roof. When water runs over these strips, it carries with it the zinc and copper needed to kill algae and lichen.


​​We answer a Frequently Asked Question every Friday! Do you have a question you need answered? Check out our other FAQs or leave us a comment!