Mac’s Mold Myths

 torontobasements.caI could happily have spent a semester listening to “Mac” McGregor Pearce speak on the topic of mold. Here are a few comments about his session. It does not do the man or the topic justice. If you have a chance to hear him or read his papers, do it. And if you have money and time to think about healthy indoor air quality, give thanks. This session made painfully clear that mold, and low indoor air quality in general are issues that plague our low income neighbors.

Mac Pearce is a firm believer in the power of the natural world. "The earth," He says,  as he puts up a slide of an achingly beautiful house sitting precariously on a cliff, "Has habits, and chances are, it’s going to hold on to those habits." We chuckle. We shift uncomfortably.

There is a not-so subtle message here: Mess with nature and you are, more or less, doomed. Over the course of his four hour presentation here at the Affordable Comfort Institute conference (#ACI 09), Mac came at this same theory from a variety of different directions. His topic was, ostensibly, mold. His approach to the subject was far-ranging, hitting upon everything from the varieties of fungus and the maligning of molds to the lives of red blood cells, and returning, like a well-honed boomerang, to the topic of living in healthy, energy efficient homes. Which brings him back to nature, and this principle:

“Nature ruthlessly favors the energy efficient over the inefficient.”

Molds are efficient. They digest their environments. That seems like a nifty trick until you consider that the environment mold is digesting and turning to dirt might be your home. While this is gruesome, I should emphasize that Mac was not a fear-mongering mold guru. On the contrary, he spent much of his time debunking fiercely guarded myths about mold, several of which I had accepted in full. Chances are, we can prevent mold build-up in our houses. And that's a whole lot easier than paying someone to come get rid of it.

Myth 1: Mold is a big risk for owners of old houses, not new houses.
Not so. Mac pointed out that in recent years we have begun building homes poorly, without adequate attention to either building science or climate. (The aforementioned house on a cliff was joined by several photos of  developments perched on swamps, and similarly misguided profit-generating headache inducing projects).  Mac laments that many of today’s houses are built with the expectation of a 30 year life, which is neither palatable nor feasible. In addition, new houses tend to be “tighter” which is counter-productive if not matched with adequate mechanical ventilation, as moisture naturally generated by occupants gets trapped, and grows mold.

This is not to say that mold is a non-issue for old houses. It’s just that building materials for old homes have a proven track record, and tend to benefit from building envelope flaws. New home building materials, including commonly used new material vapor barriers – have no track record. We don’t know whether they will hold up at all. To prevent mold build up - avoid air-tight spaces that can trap moist air. Mold loves moisture (not water, moisture).  Old drafty houses have the upper hand on the mold front for this reason - but you pay for that privilege with your heating bill.

Myth #2: Mold is the biggest risk to indoor air quality.
Nope. The biggest risk is  Carbon Monoxide.  I’ll delve into that more in the next blog. But Get A Monitor!  Carbon Monoxide kills people.

Myth #3 If you can’t see it or smell it, mold is not a problem.
Dang. Wish this was true. It’s not.  Mold comes in myriad colors, shapes sizes, growth rates, and levels of toxicity. Some smell horrible, some don’t smell at all. (And it goes without saying that Mac is fascinated by all of them).

Myth #4 Mold is a huge health issue for most homeowners.
Mold is a huge health issue for some people. Mac is not one of them. His many mold eradicating efforts have caused him not much more than a bad taste in his mouth, curable with beer at the end of the day. And this, he points out, is true even of harrowing “Black Toxic Mold” (Stachybotrys) which “Is dangerous…if you lick it. So don’t lick it.”).  For others, simply walking into a house where mold is present (even if it’s behind the wallpaper, in the basement) can be devastating, requiring hospitalization. Mac told the story of a child whose asthma was horrific, suddenly taking a stranglehold over her. Her asthma attack occurred several months after a major leak that was inadequately eradicated. Horrible? You bet. And frightfully expensive to get that house back in safe working order... all because the area that was flooded never was properly cleaned and ventilated.  A penny saved....

*McGregor Pearce, according to the Affordable Comfort Institute Conference 09 brochure, is environmental health consultant who is a pioneer in studying the relationship between mold and indoor air quality. He has investigated thousands of homes and buildings for mold and moisture problems and has taught hundreds of classes and seminars on IAQ-related issues.


If you’re in doubt of any unpleasant growth in your house, you should simply assume there is a problem whenever you see mold or smell mold odors. Testing should never take the place of visual inspection (which is recommended) and it should never use up resources that are needed to correct moisture problems and remove visible growth.
People used to think that molds were harmless but it isn’t. The fact is, some molds produce a toxin called aflatoxin (toxic and among the most carcinogenic substances known) that causes illness and death in people.
Sometimes, mold growth is hidden and difficult or hard to locate and find. In such cases, carefully conducted sampling and visual inspection may help determine the location of contamination. However, mold testing is rarely useful for trying to answer questions or inquiries about health concerns. For more information, see mold testing services

I had my home tested by Mac years ago and he found Stachybotrys. We ended up taring down our house. I need our new home tested and was wondering if Mac is still around. Thanks Martha

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