Time to think about moisture and mold - especially in the wet Lower Mainland
One of the most common mistakes homeowners make is controlling the air quality and humidity in their home. Quite often in older homes, the idea of keeping the secondary or summer fan running all the time is an anathema to owners. Some actually believe it's an unnecessary expense; however by reducing air flow and allowing humidity to increase, they are creating a perfect environment for mold. Newer heating systems are much smarter and have a fan running all the time. I've actually been asked how to turn the fan off, to save money. In fact, that constant flow of air throughout the rooms is the best way to control mold and mildew.
To control molds, let's consider how they grow. In order for residential types of molds to grow, they need only nutrients, spores and excess moisture, so control might involve withholding one or more of the essentials. Because there is a mold for virtually every nutrient, it is impossible to control molds by eliminating nutrients.
The spores (fungal “seeds”) are waiting virtually everywhere, sometimes for years, for the right conditions. Some spores can germinate in as little as four to 12 hours, and, if left undisturbed, fungi can grow and spread in 24 to 72 hours. It’s impossible to control mold by eliminating all spores, although controlling the spore count can reduce the potential population of growing mold.
Spores are large enough to be captured by filtration. So here's a tip... keep your filters clean, if they are reusable and cleanable, or change them every three months.
The key to residential mold control is controlling moisture. For mold to grow on the surface of a material, its “water activity” level must be 70 percent or higher for nearly all molds. Water activity level of a solid material is defined as the moisture level resulting from the material being in air of the indicated relative humidity long enough to stabilize. The relative humidity of the air at the material is more important than the air in the center of the room, and it may be different. A common example is when wall is colder than the ambient room, its water activity level increases. Materials vary in the time required to stabilize, but a day or two is sufficient for some materials to take on sufficient moisture to support mold growth.
A year or two ago I noticed a moisture problem in my master bathtub/shower. In the interim, prior to full replacement of the shower wall unit, I'm ensuring every time there's a shower, that the wall is dried off, especially at moisture entry areas, and I make sure that the bathroom fan is on. We have a measured humidifier fan in our master bath, so it's kept at less than 40 percent humidity to keep the area dry and reducing the potential growth of mold.