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Top Causes of Indoor Moisture in Chicago

indoor moisture caused by window condensation

At Indoor Science, we compiled a list of the most prevalent indoor causes of moisture problems for 100 homes in the Chicago area over the span of 6 months from August 2017 to January 2018. These were homes in which we performed mold or moisture inspections. In this blog post, I will discuss some of the most common moisture problems we encountered. These include water intrusion from external sources, damp foundations, plumbing leaks, insufficient management of moisture sources, and thermal bridging.

The most common cause of dampness is moisture intrusion from an external source. 54% of the homes in our analysis had this problem. These problems are typically caused by a roof leak or window leak during a heavy rain or ice damming. Leaks in roofs are commonly caused by damaged or missing shingles, weakness at penetration points, and failing flashing. Window leaks may be caused by failing caulk or sealant around the window frame.

The second most common moisture problem is wet foundations. For the 100 homes we analyzed, 23% had this problem. These are usually caused by a crack in the foundation.These cracks can form either from the soil subsidence around and beneath the home and in rarer cases improper curing of the concrete. However, these cracks are not necessarily caused by the home shifting. In fact, gutters and downspout are sometimes the culprits. When downspouts are clogged, causing water from the roof to pool around the foundation. Also if the soil around the home is sloping toward the foundation, water can pool around the exterior walls and exert pressure on the wall leading to moisture intrusion. Plants that are in close proximity to the foundation can also damage the foundation walls with its root system by exerting too much pressure on the wall. Lastly, the freeze/thaw cycle during winter can damage foundations. As water freezes after being absorbed into the foundation wall, it expands causing fissures to form.

20% of the homes in our analysis had moisture problems associated with plumbing leaks. Many problems arise from broken seals. Seals typically degrade with age and cause leaks in areas such as dishwashers, bathtubs, and toilets. Another common cause of leaks can be from temperature changes. When pipes are exposed to freezing temperatures this can cause water to freeze and expand, rupturing the pipe. The most common in my experience is the corrosion of pipes. Corrosion is the process by which a refined metal attempts to chemically stabilize itself into an oxide. This typically leads to rust formation inside the pipe causing degradation. The average lifespan of a pipe depending on the composition can range from 20-70+ years. As the degradation continues with age, the structural integrity of the pipe gets weaker.

The final common moisture issues often linked together are the improper management of indoor moisture sources and thermal bridging. Improper management of moisture sources often happens in bathrooms and kitchens. In bathrooms, the most common moisture source is humidity generated from showers. In an ideal situation, the humidity would be exhausted to the outdoors by an exhaust fan. However, sometimes the exhaust fans are not pulling an adequate amount of humidity out and may need to run longer than current usage. In some cases, there is no exhaust fan present which can send humidity throughout the home and may diffuse into a cold wall or above the bathroom into an attic. In the kitchen, the most common source of humidity is from cooking activities. As water reaches 212 degrees Fahrenheit, it begins to boil. Combustion of gas burners also gives off humidity.  This humidity is often managed by turning on the stove hood to exhaust the moisture out. However, many exhausts do not exhaust outdoors and are in fact recirculating the air. And in other cases, some homeowners do not operate the exhaust.

This leads us to moisture issues associated with thermal bridging. Thermal bridging refers to an object or area that is more thermally conductive than the surrounding areas. Many objects in the winter can become thermal bridges such as exterior walls, HVAC ducts/vents, windows, etc. When moisture is improperly vented in the home, it can condense on cold surfaces caused by thermal bridging. For example, if a bathroom improperly vents moisture, it may condense on walls where there are studs due to thermal bridging.

While these are some of the most common sources of moisture that we investigate, there is myriad of others that we also come across. These moisture issues can often lead to the formation of mold growth. If you suspect that your home has one of these moisture issues and are concerned with mold, please reach out to us to assess your property.

Ian Cull

Ian Cull is a nationally recognized expert in the field of indoor air quality. He is the Chief Science Officer of Indoor Science, a company he started in 2004. He speaks around the world on air quality topics and is a training provider of the Indoor Air Quality Association. Mr. Cull is a Licensed Professional Engineer (PE) and Certified Industrial Hygienist (CIH). His degree is in Environmental Engineering from the University of Illinois - Urbana Champaign. Mr. Cull has developed 50 air quality related courses for the IAQA University and is the author of the book, “Fundamentals of Mold Remediation”. In his words… “Besides being passionate about indoor air quality, I enjoy cycling, music, the Chicago Bulls, and having fun with my three kids.”