WHAT CAUSES MOLD AND ALGAE TO GROW ON ROOFS?  – FAMILY ROOFING

Posted on by David Reid

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WHAT CAUSES MOLD AND ALGAE TO GROW ON ROOFS? 

The black streaks on your roof that look like mold are actually a species of blue-green algae known as Gloeocapsa Magma.  These algae are carried by airborne spores and are extremely prominent in areas with humid climates.  When the spores settle on the roof, they feed on heat from sunlight, moisture from outdoor humidity, and nutrients from roof materials to grow and spread out.  With enough growth, the blue-green algae will eventually take on a black color and cause the unsightly appearance that no homeowner is fond of.

WHY IS IT A PROBLEM?

Besides making your roof look funky and dirty from discoloration, roof algae don’t have many short-term consequences.  In fact, the majority of the damage is produced in the long-run.  Since algae is a living organism that needs food to grow, its first (and possibly only) source of nutrients is the limestone in your roof’s shingles.  With time, the algae will eat through the shingles, inviting moisture and debris inside.  This affects the roof’s structural integrity and paves the way for even more problems, such as mold growth, water damage, etc.  Plus, there are the added troubles of algae retaining large amounts of water and creating temperature inconsistencies in your home.

Your roof is important to the integrity of your home & the lifespan of your roof is highly affected by the weather and its environment.  How about the roof that seems like it gets dirty really quickly.  If you’re in a humid part of the country, you know what it’s like as it appears almost overnight to be covered in black stains, discolored streaks and/or green mossy growth.

ALGAE

They like dampness and shade, so algae spores can grow on wood shingles or shakes and asphalt shingles that don’t get much sunlight.  Because roof algae retain moisture, they can cause shingles to deteriorate and eventually rot completely.  Algae also like the humid conditions in gutters and downspouts and can grow there as well.  Algae are recognizable by their black-green coloring.

MOSS

It likes moisture, so it typically grows on moist wood shingles or shakes.  As the moss grows, it contains even more moisture, all resting on the surface of your roof.  Eventually, your roofing materials begin to rot, compromising the integrity of your roof.

MOLD

Appearing as fuzzy black, brown, or green spots or slimy film, mold is attracted to damp or humid environments and spreads quickly.  Black mold is the most dangerous type of mold. It lives on wood, paper and drywall, so if the problem is not addressed quickly, it could weaken the entire structure of a home or building.  Easily recognizable by its dark black color and its strong musty smell, black mold is toxic and can cause serious respiratory illnesses in occupants of the home or building.

Algae Growth

The black streaks on your roof don’t appear for everyone.  They usually only appear on roofs in humid parts of the country.  Black algae or roof mold is usually blamed on dirt accumulation, mold and mildew or defective shingles.  It’s actually just a blue-green algae spread by airborne spores.  It is easily spread and causes those colorful stains on so many roofs.  It needs heat, moisture and nutrients to grow.  The sun and the humidity on your roof give it the first two.  The third ingredient, nutrients, is gained when the spores begin to eat the limestone filler in your roof’s shingles.  Feeding on the inorganic materials of your roof’s materials, they’ll continue to spread and darken until you get rid of them.

So a mossy algae that eats your roof doesn’t sound too bad on its own.  But that’s not all that it is.  It doesn’t just affect the appearance of your roof.  It affects the structural aspect of it as well, which can lead to structural damage to your home.  When the limestone and other granules are digested out of your shingles, it makes way for more problems.  Moisture and water can get in to your home through the holes in your roof and down to the wood underneath.

Mold and Mildew Growth

As you can see, the alga gets on your roof easily enough.  The wind just has to blow in the right direction and there it is.  Just as easily, mold and mildew follow.  The standing water and humidity, the rapidly growing spores and wood rot, these are quick and fertile breeding places for mold.  This can be expansive, and as a result, expensive.  Often the damage is done well before it’s discovered, as mold on the outside of the house is usually indicative of mold on the inside of the house.

You can’t prevent spores of algae and moss or mildew from landing on your roof. But you can prevent growth.  Obviously, the best care is preventative care.  With regular cleanings you can get rid of the algae before it even becomes an issue, and definitely before it gives way to rot, mold and mildew.

How to get rid of algae and mold?

If your roof is super bad, make sure you consult someone professional before taking action.  Why spend money cleaning a roof when it needs a repair. In that same vein, why repair a roof when it just needs a cleaning?  But luckily (especially when paid attention to) most of the time to remove algae and mold your roof will just need a good, thorough cleaning.

One way to clean the roof of algae and moss is with a brush and a little grunt work, scrubbing and separating the greens from the roof.  Brushing should start at the top and work down, as going up could mess up your shingles.  Bleach shouldn’t be used either because it can damage your roof.  You should use an environmentally friendly and safe roof cleaning solution.

How can I stop it from happening?

Well, you can get zinc strips if you’re concerned about stopping the algae from growing on your shingle roof.  However, if you’re in a humid area and have a different type of roof, you really can’t stop it. It is advisable to trim trees back if they’re close to your roof. Not only will this stop small branches from falling off your roof but it will not give the algae a place to grow easier.

WHAT CAN BE DONE TO PREVENT ROOF ROT

Mold, mildew, moss and algae spores exist in the air, but they won’t start growing on your roof if the right living environment isn’t there.  The best way to spot and treat roof mold and mildew and roof moss and algae problems before they grow out of control is through biannual roof inspections.

Often times, roof fungus can enter a home through a hidden roof leak.  Water draining off the roof seeps into the interior of a structure, creating an environment where black mold or mildew can form.  Only a professional roofing inspection will reveal this problem.

There are also some preventive measures homeowners and commercial property owners can do to safeguard their roofing systems from fungus. Here are some tips:

  • Trim away any trees touching your roof to prevent algae from growing.

  • Keep your gutters clean so moisture properly drains through them, preventing moss, mold and mildew.

  • If you live in weather conditions that foster algae, mold, mildew and moss growth, consider paying more for roofing materials or techniques that resist their growth. It will be worth the few extra dollars in the long run.

  • Improve your ventilation inside and out. For your roof, ridge vents provide the utmost aeration. Contact us for more information about roof ridge vents.

Proper care and maintenance is essential for the long-term performance of your roof. A roof inspection, especially after a storm, is a major component to proper roof maintenance.