Why does green algae grow on siding?
Have you ever wondered why green algae grows on siding? You’re not alone! Let us walk you through the basics – the fun stuff is at the end.
Algae Growth Principles
First, let’s adjust our thinking. The five core environmental factors that promote algae growth on siding are:
- Moisture – Constantly kept damp.
- Shade – Algae cannot tolerate the intensity of the sun.
- Hungry – Fed by tree sugars, sap, pollen, bacteria, fertilizers and more.
- Air Flow – No new air is pushing out the old.
- Source – Algae spores come from pools, lakes, rivers… water sources
Algae isn’t growing on siding all around your home, right? That’s because your home has a number of micro-environments. From a high-level view, this is four unique sides of your home. But, we’ll need to break it down in further detail to understand why you see algae growing on your siding.
Micro-Environments Promote Algae Growth
- Siding light levels
- Siding kept damp behind bushes
- Low air flow/shaded areas around a chimney
- Difference in terrain beneath your siding – Mulch absorbs water where concrete quickly dries
- Nearby retention ponds, rivers and lakes
- Poor drainage from downspout/Leaking sump pump
The list goes on. While your macro-environment plays a critical role, such as if you live in the humid southeast, seasonal midwest or dry southwest, these micro-environments determine where algae spores can survive. We understand now that small environmental differences greatly influence where algae grows on your siding.
Remember, NEVER pressure wash thin plastic siding. Doing so can permanently damage your home, void warranties and it will not disinfect the problematic spores.
Types of algae on siding
Although there are over 8,000 species of green algae, we categorize algae growing on siding in two general ways.
- Blooming Algae
- Condensation Algae
Blooming algae turns your beautiful home into the eyesore of the neighborhood. A dirty diamond devalued by its poor curb appeal. Algae blooms across the length of your siding and is easily seen from the street.
Algae blooms on siding are largely associated with the five core principles of algal growth while blooming across northern exposures of the home.
Condensation algae is only visible on the underside of your siding plank. We consider this different because it requires a lot more effort to disinfect. Why? It typically has gone unnoticed for years and is now a thick, dense layer of algal bio-film.
Algae growing on siding from condensation is due to moisture draining behind the siding. Siding has small weep holes to allow moisture trapped behind it to escape. This moisture flows out the weep hole and works across the underside of the siding due to surface tension. We even find this on the sunny side of homes. As long as it can stay out of direct sunlight, condensation algae will grow on your siding.
Why is there moisture behind my siding?
Algae anywhere on siding is largely associated with condensation.
So, we ask, “Does your siding sweat?”
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