Are Passive Solar Homes More Resistant To Mold And Other Infestations?

Are passive solar homes more resistant to mold and other infestations? Concrete and anti-microbial materials keep mold and insects from damaging a passive solar home. Frederick Bernard, the owner of Acorn...

Frederick Bernard, the owner of Acorn Builders, a custom home designer, builder, and remodeler, says, "There's a new science in building materials called 'anti-microbials.'" These are materials that are "either sprayed on a home or used in the composition of certain materials to prevent mold." Bernard describes the anti-microbials as "microscopic needles" and says, "They don't bother us, but single-celled organisms can't grow on them because the needles puncture the single-celled organisms and cause them to dehydrate and die."


Bernard says he first heard about anti-microbials "being used in fiber mesh, which is a polyester fiber that they put in concrete to strengthen it and to eliminate the need for a lot of steel. They put an anti-microbial in it, and it was supposed to keep concretes from getting moldy. I thought it was very interesting. And I even read in a building magazine that some manufacturers were making anti-microbial steel now for steel framing, for light steel."




"Concrete," Bernard says, "is made with Portland cement. It's pretty much waterproof. They make water tanks out of it. It's a good heat sink or thermal mass in the sense that it conducts heat pretty rapidly." Thermal masses such as concrete are important features of passive solar homes. They are used to store heat from the sun. They absorb heat from the sun during the day and release it slowly at night when the house cools down. Bernard says that concrete "absorbs heat quickly and expels heat pretty fast."

Mold grows where there is moisture. Bernard says that concrete "does not allow moisture to pass through it, so it retains the moisture that absorbs into it," which means that it will have a tendency to get moldy. He says that "if you were to use a concrete that was made with a different hardener, such as lime or magnesium oxide, both of which are both extremely breathable and allow moisture to pass through them, you would have less chance of getting mold on those because they don't actually retain moisture. They would allow it to come and go according to the humidity in the air. Also, they are less conductive."

Adobe is another material used in passive solar houses. It's especially popular in the American Southwest. Adobe is made of clay and straw. Bernard says, "Anything made with sand is going to have the same conductivity as the sand in it. With adobe products, which are made with clay, the sand acts as a filler and holds the clay together. But the clay itself is the majority of the material. Clay has a very slow rate of heat transfer, which makes it a good heat sink and a good insulator as well. The reason for that is as the clay wall heats up, it takes a long time for that heat to pass into the clay and a long time to leave it. That's why clay materials are better used as thermal mass in what we call 'solar' houses. But they're really just efficient houses."

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