Mold & Mildew - Issues out of thin air
Mold and mildew are among the most dreaded home performance issues. No one wants to see mold and mildew in their home, or a home they are considering purchasing.
Getting to the root of the problem, rather than treating the symptoms is the best approach. The best way to do this is concentrating on the basics.
Mold is natures recycling agent. When a tree falls in the forest, the process of being broken down into nutrients for future plant growth immediately begins. If it weren’t for mold, fungus and other parasitic organisms, there would be no rich and fertile soil. Unfortunately, what is good in nature is bad in our home.
Solving mold and mildew issues begins with understanding them. We will keep it extremely basic and simple here, this article isn’t targeted towards the scientific community, it’s for “the rest of us”.
In order for mold to form, it must 
have 3 things, moisture, favorable temperatures and food. In building performance, only moisture is easily addressable. We find it most comfortable at around the exact same temperatures as mold. Our homes are built from organic substances such as wood, paper and fabrics that mold can easily use as a source for food. Moisture management is therefore, the “holy grail” of mold and mildew prevention.
The first step in solving a mold or mildew problem, is realizing that what you are really facing is a moisture management problem that causes mold or mildew.
Moisture on organic building surfaces is sometimes a bit difficult to pinpoint. When I was a kid, one of my Dad’s pet sayings, which I hated at the time, but now find myself telling my kids is; “it didn’t just appear out of thin air”. Ironically, many mold and mildew issues do happen from thin air, specifically the warm and moist type, commonly found in our homes and buildings.
To understand this, we need to get to the basics of the moisture cycle. The moisture cycle is really a simple, easy to understand concept, hidden in scientific mumble jumble that get’s everyone confused. Keep it simple. Standing water evaporates. Warm water evaporates faster than cold water. Think of a glass of ice water as compared to a boiling pot of water. When water evaporates, it literally disappears into thin air. Or does it?
You walk outside your home to get the newspaper on a chilly May morning, your shoes are nowhere to be found and you venture outside, wearing only socks on your feet. It hasn’t rained in days, you tell yourself, I don’t need shoes. You step on your lawn, and instantly realize the grass is soaking wet. It wasn’t the sprinklers that wet the grass; it was “morning dew”.
In one of the few examples where a scientific phenomenon actually carries an easy to understand name, scientists named the magical temperature where water appears out of thin air, the dew point. Without getting scientific on you, the dew point is a function of the relative humidity of air and temperature. The higher the relative humidity, the higher the dewpoint; when a surface falls in temperature to the dew point, water will form from thin air.
Now we get to the issue at hand, solving the mold and mildew issue where no smoking gun, such as a roof leak or plumbing leak is the root cause.
Humans are happiest at around 70 degrees Fahrenheit, with around 40-50% relative humidity. If the humidity drops below that point, dry skin and upper respiratory issues happen. Above it mold and mildew thrive.
Home performance is a balancing act. We strive to maintain safe and comfortable humidity levels, while preventing any surfaces in our homes from reaching the dreaded dew-point.
The simple solution to mold and mildew issues in our homes and businesses are maintaining comfortable humidity levels and temperatures, while preventing dew point on any surfaces. Going back to the 40-50% relative humidity ideal range, we can determine what the dew point is. In any given building, the precise dew point is measured by a digital hygrometer.
At 45% relative humidity and 70° F the dewpoint is 48°. Increase the Relative humidity to 80%, and the temperature to 75° (Commonly found in the bathroom after a hot shower) and dewpoint becomes 64°. Insulating a home to prevent any surface from reaching 48° is relatively easy, preventing them from reaching 64° pretty difficult. This is why bathrooms are the most common rooms in the house for mold issues. We solve this problem by installing a vent fan, properly vented to the exterior, to keep humidity levels at an acceptable level.
Mold and Mildew formation is a complex interaction of temperature, relative humidity, proper ventilation and thermal performance. Slabs on grade, crawlspaces and basements, bathrooms, kitchens and attics are the most common areas in a home where moisture management requires a thorough understanding of the moisture cycle. The proper tools to solve complex mold and mildew issues include a digital hygrometer that reads actual dew points, an infrared camera that identifies areas at or below dew point and a moisture detector to verify the presence of moisture.
Unfortunately, mold and mildew issues can appear out of thin air, contrary to what my dad, and in turn I preach!
Steve McKenna
Director – Building Efficiency.
Murtha Construction.
Link to this article: www.murthaconstruction.com/BuildingEfficiency/Articles/MoldandMildewIssuesfromthinair.aspx