Attics, Moisture, and Mold: Part 2

Posted on September 19, 2018 in Attic Ventilation

attic mold

In part 1 of our “Attics, Moisture, and Mold” blog series, our roofing installation company shed some light on moisture conditions, how mold grows, and what you can do to reduce the moisture in your home. In part 2, we’ll continue our discussion:

Humidity vs. Moisture

You’ve probably heard both of these terms used to describe the presence of water vapor, so what’s the difference? Moisture usually refers to water vapor that’s found on a surface, while humidity usually refers to water vapor that’s found in the air. When you listen to the weather forecast, you’ll hear the expert use the term “humid” to describe a warm, sticky day.

Relative Humidity

Though relative humidity is another measurement of humidity, the two terms aren’t interchangeable. Relative humidity (abbreviated RH) is expressed in a percentage, and refers to the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Humidity, also called “absolute humidity (AH)” refers to the amount of atmospheric moisture present.

For example: If one day, the dew point is 34 degrees Fahrenheit and the temperature is 38 degrees Fahrenheit, we would get a high RH value and a low AH value. If another day, the dew point is 63 degrees and the temperature is 85 degrees, we would get a low RH value, but a high AH value.

The Effects of Seasonal Changes

When it comes to moisture, the seasons have an effect on its presence. When the weather gets warmer, humidity causes your attic to collect moisture and promotes the growth of mold. The highest RH level that building codes and manufacturers recommend is 40%. If your home is over that during the summertime, it could overwhelm your attic ventilation system and increase your attic moisture.

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