How Basements Affect Your Ambient Air Quality
By: Stephen Andrews
When most people think of basements, they picture dark, musty spaces filled with cobwebs. Or perhaps they remember having to sweep out excess water after a big rain. A good waterproofing company can handle the flooding issues, but did you know that there are methods that you can use to improve your indoor ambient air quality by improving the basement? Most people are unaware that the problem of excess moisture in the home actually starts down there.
For the past few years, there has been a growing trend towards conditioning all areas of the house – including basements and crawl spaces. As building science is evolving, more and more industry leaders such as the National Comfort Institute, ASHRAE, and eco-friendly organizations such as Southface and the US Green Building Council are taking a serious look at the relationship between building techniques and indoor ambient air quality. As a result, many people are turning to their basements and crawl spaces for answers to health issues caused by excess moisture in the home.
If you look at the history of building in general, you can see how this trend is part of the overall evolution of building techniques, especially the design of a building’s foundation. A hundred years ago, people built log homes directly on the ground. They didn’t have basements to be concerned about, and they probably just expected to replace the wood that became rotten or infested with termites. Eventually someone figured out that if the home was raised up and put on stilts or pilings, that they could avoid or eliminate those problems. But there was a price to pay-homes that were built off the ground were colder and less comfortable to live in.
The next step in the evolutionary process was to enclose the foundation to insulate it from the cold weather. But spaces that were open to the ground and closed up too tightly began to have problems as well. Enter the ubiquitous crawl space vents. Just enough ventilation, it was reasoned, to allow the moisture and radon to leave, but not so much as to lose too much heat.
Unfortunately, as crawl spaces were being opened up, air conditioning was also becoming more common in homes, creating a different problem: the indoor dew point condition. In some climates, vents were bringing in hot and humid air into the crawl space, while the floor above it was being cooled. The difference in the temperatures created the perfect condition to condense the moisture in the crawl space-right onto the floor joists and sub-flooring. This created a potential mold problem that could permeate the entire home.
So what is the answer? We know you can’t just seal off the vents to prevent the moisture from migrating in, and it is not financially feasible to air condition a crawl space. The answer, then, lies in fighting fire with fire. In other words, use technology to solve the problems that technology has created. Utilize the best waterproofing methods you have, but don’t stop there. Install durable vapor barriers, which are taped together and sealed to the wall. Seal off the basement vents, but don’t forget to add a method for providing makeup air and dehumidification to prevent indoor dew point conditions. Most importantly, become educated on how buildings function as a system. Learn as much as you can because building science is in the process of taking another evolutionary step- and right now whether you are building, renovating, or waterproofing your home, taking steps to improve the condition of your basement will improve the overall indoor ambient air quality in your home.