The Trouble with Mold, Mildew, Moss, and Algae on Your Roof

Old And Covered With Moss Wavy Roof Slates Covers The Barn.

Mold, mildew, moss, and algae aren’t the most aesthetically pleasing things to have on your roof. But can they actually hurt anything aside from curb appeal? Today we discuss the impact of these things on your roof. Let’s start out by defining what they are:

Mildew and Mold

Are forms of fungus. They are closely related but differentiated by color. Mildew is white and mold is black, blue, red, or green. Both have unpleasant odors and are linked to causing certain health issues in humans.


Is a small, non-vascular flowerless plant. Moss typically forms dense green clumps or mats, and is often found in damp or shady locations. Since it doesn’t have roots it absorbs water from its appendages or spores. The lack of roots also lets it grow upward and often out of control.


Is a group of predominantly aquatic, photosynthetic, and nucleus-bearing organisms that lack the true roots, stems, leaves, and specialized multicellular reproductive structures of plants. Basically algae doesn’t have roots, loves water, and eats sunshine so it can grow like crazy in standing water.


All three of these are more likely to grow if you live in a wet or humid climate.


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The Trouble with Mold and Mildew 

On their own mold and mildew tend to show up as streaks on your roof. Since they are normally black in color they are most noticeable on lighter colored shingles. They are most commonly found growing by themselves in warm, humid climates. 

Your Health

Since it’s outside its impact on your health may seem negligible, mold spores have a knack for finding their way into the home.  They can travel through the roof itself, which is much easier if it’s been damaged and has holes in it. Spores can also get in via things like HVAC systems. Once it’s in there, spores are pumping through your whole house. Or it can be washed off during storms and tracked in that way. 


Mold and mildew have a way of seeping in anywhere that is dark and wet. While they can’t pry up shingles without the help of buddies like moss they can still do some damage. Unchecked mold and mildew will eat away and erode roofing materials. The fact that they tend to burrow just makes this damage even worse and more costly to fix.

Attracts Sunlight

Since mold tends to be dark in color it attracts sunlight. This sunlight is going to heat up your roof and your home, costing you in utility bills. The fact that it can blanket a roof rather quickly just exacerbates this issue. 

The Trouble with Moss

So what’s the big deal? Some people like a rustic look or just don’t mind the appearance of moss. Why is this such a problem?  


Since moss tends to grow rapidly and in clusters those clusters take in water. The excess water makes it very heavy. Extra or unnecessary weight on your roof is never advised. If left unchecked it can blanket your whole roof causing even more strain. 

Mold and Rot

This excess standing water also means it encourages mold growth. When mold is growing due to moss, pieces can break off and be tracked directly into the home. Which, as stated above, can cause serious health risks. But mold and standing water both lead to rot. Simply put, a rotten roof is a seriously damaged roof.


Rot can create holes but so can the moss itself. With how invasive moss is, it’s not uncommon for it to find its way under shingles, tiles, and slates. Uprooting those parts of your roof creates holes which makes you more prone to leaks and even more rot. 

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The Trouble with Algae

Much like moss, mold, and mildew, algae starts as an aesthetic issue. Most homeowners find out they have roof algae when they see black streaks (just like mold), dark spots, or green fuzzy moss on their roof. While these stains can be permanent, as you’ve probably already figured out, the issues aren’t limited to curb appeal. 


Algae loves stagnant water so if you have algae, you have standing water. And standing water loves to get anywhere it shouldn’t be. This water seeps in and softens the wood in your roof which leads to rot. This has serious, irreparable, consequences on the lifespan of your roof. 


In addition to rot algae if left to its own devices can make tiles irreparable. Damaged tiles make the roof’s wood even more vulnerable to water. 


Yup, our old buddy mold is back. Standing water along with algae spores are another breeding ground for mold. 

They Can Spread

What starts as just roof algae probably won’t stay that way for long. Algae spores can travel on the wind. So it won’t be long until you see it growing on roofs of sheds, barns, and carports. It can even travel off your property onto your neighbor’s roof. Do you really want to be the person who gave the whole neighborhood algae?


The bottom line is mildew, mold, moss, and algae can all seriously damage your roof. This damage is even worse when they team up. But even more importantly once mold is involved, your health is at serious risk. Even people without asthma or mold sensitivities can develop long term health problems due to it. As important as a healthy roof is, your health, and the health of anyone living in the home, should always be top priority. 


If you suspect your roof has mildew, mold, moss, or algae give us a call today at (636) 699-0449 or request your free inspection today. You can also follow us on Facebook, LinkedIn, Instagram, and Twitter. If you’re in the St. Charles County area and looking for an experienced roofing and siding contractor, we are bringing forth over 20 years of experience in the roofing industry. That’s something you can trust and especially if we’re in your neck of the woods.