Roof Moss, Algae & Mold: How to Identify and Remove Roof Growth in Wisconsin

A Guide to Roof Growth in Wisconsin

When you spot discoloration or dark streaks on your home, your first thought is usually: What’s growing on my roof, and how do I get rid of it?

Whether it’s roof moss, mold, mildew, algae, or lichens, these organisms do more than lower your curb appeal. Left untreated, roof growth retains moisture, causes shingles to decay, and leads to costly structural rot.

Here is everything Wisconsin homeowners need to know about identifying roof growth, preventing damage, and safely removing it.

What Causes Roof Growth?

Roof moss, mold, and algae thrive in cool, damp, and shaded environments. Around the Midwest, we typically see these kinds of roof problems crop up in spring and summer when there’s lots of rain and humidity.

Common triggers include:

Overhanging tree branches that block sunlight.
Clogged gutters holding excess moisture.
Flat or low-slope roofs with poor drainage systems.
Heavy shade on northern-facing roof slopes.

Roof Moss vs. Mold vs. Algae: How to Identify the Difference?

Moss: Heavy moss growth on roof shingles is especially destructive. Moss commonly grows on wood or shake shingles, as well as asphalt shingles. Because of how thick moss is, it holds more moisture than mold, mildew or algae. Its ability to retain lots of moisture means roof materials begin to break down and rot quickly, leaving the structural integrity of your roof vulnerable.

Mold: Mold looks fuzzy or slimy and often manifests as black, brown or green. Black mold is the most dangerous and weakens the structure of your roof quickly. If it’s allowed to spread, it can easily make its way into your home, causing even more problems, including health problems for your family and pets. The good news is that Wisconsin has one of the lowest mold rates in the US.

Mildew: Mildew is more powdery in nature. It’s often found on roofs with poor drainage or places where trees hang over the house. Green, black, red & pink mildew are quick to spread!

Algae: Algae is typically blue-green or black-green in color. It often shows up on wood or shake shingles, as well as asphalt shingles that don’t get very much sun. Algae is also common in gutters and downspouts. Wisconsin is especially susceptible to algae roof stains since we’re in a high algae growth region.

Lichens: Lichens are organisms that develop from algae and fungus. They can manifest in a variety of colors, sizes and forms. Lichens are extremely hardy, and can grow in nearly any environment and on nearly any surface, including rocks and trees. Lichens also spread very easily – usually through the wind.

How to Get Rid of Roof Moss and Algae Safely

If you notice roof stains or moss buildup, take these action steps to restore your roof:

Trim Overhanging Trees: Cut back branches to allow direct sunlight to dry out wet roof surfaces.
Apply Chemical Cleaners (No Power Washing!): Treat growth using specialized chemical cleaners like Wet & Forget or Moss Out. Never use a high-pressure power washer, as intense water pressure strips protective mineral granules right off your asphalt shingles.
Upgrade to Algae-Resistant Shingles: If it’s time for a roof replacement, install shingles embedded with copper granules, which naturally prevent algae spores from growing.
Install Zinc or Copper Strips: Metal strips installed along the roof ridge release tiny amounts of zinc or copper ions when it rains, creating an environment where moss and algae cannot survive.
Clean Gutters Regularly: Keep gutters clear so water flows freely away from the roof edge.

Protect Your Roof with Reimer Roofing & Remodeling

Ignoring roof growth can lead to expensive leaks and premature roof replacement. If you aren’t sure how to safely treat your roof, let the local experts help.

Need help identifying or removing growth? Schedule a professional roof inspection in Wisconsin with Reimer Roofing & Remodeling today!