Mold needs four things to live: a temperature of 41 to 104 degrees; sufficient moisture content; oxygen and food. Mold is like a four legged stool, if you knock one leg out the stool falls over. If mold does occur in buildings there are very well established guidelines for remediation. Mold does not consume building materials, it does not cause structural issues – fungus does – which occurs at a higher moisture content than mold. Mold is more common and can be dried out, killed, and wiped away. If you keep the area dry from that point on, you will not have further problems. People develop issues with mold when it becomes active and releases spores into the air. Those spores are inhaled and, like ragweed, can cause an allergic reaction. The trick is to control the elements of the four-legged stool. But how do we control these elements?
Temperature is something we create. We know that mold’s sweet spot is 41 to 104 degrees and I guarantee that you can find that temperature range in just about any wall anywhere in any season.
Oxygen – you’re not going to get rid of oxygen unless you build your building on the moon.
Food – starch or sugar typically are the food sources for mold. You can try to build a building that is food free but I guarantee you food will show up. A perfect example of how a food free environment doesn’t last is your shower, which is generally ceramic, glazed tile, glass, chrome, vinyl – there are no starches or sugars in these materials – but mold will grow because food shows up in things like soap. Starch is one of the binders for soap. That’s the problem with trying to develop buildings without food sources, because food will show up in the form of contamination through the use and occupancy of the building.
The accepted strategy among building designers and construction professionals is to control the moisture so that you do not have a17% wood moisture content in materials. This is the moisture content at which mold will appear.
We’ve never really been able to completely keep moisture out of our building constructions. The trick is to build living, breathing, drying assemblies that keep moisture content levels low. You can live with bursts above the 17% as long as you get the water out before the mold begins to propagate. If mold does occur in your building, deal with it in a considerate and rational approach: Protect people from exposure to the airborne spores, clean it up, dry out the substrate, and prevent the surface from achieving elevated moisture contents in the future.
Lucas Hamilton is Manager, Building Science Applications at CertainTeed Corporation.
Nolan Day, Architectural Systems Manager at CertainTeed Corporation contributed to this blog.