Mold continues to be a major issue for architects, contractors, and building owners alike. Because mold can release VOCs, produce allergens, and in general affect a building’s indoor air quality, mold development has the potential to impact the health of a building’s occupants.
To maintain a healthy indoor environment, it is important to mitigate and prevent mold growth in interior spaces. Yet anyone searching for information about mold in buildings will be overwhelmed by the sheer volume of sources—a cursory Internet search on mold reveals more than 40 million references. Given the amount of information available, it can be difficult to gain a clear understanding of what’s important about mold and, equally critical, to discern what’s accurate and what’s not when it comes to preventing mold development and its associated impacts.
There are many misperceptions about mold, but one of the most common is that the presence of paper, wood, and similar organic materials increases the likelihood of mold growth in a building. In reality, mold can grow on almost any surface where dust, dirt, or organic films can accumulate. This includes not only wood and paper, but also carpet, glass, fiberglass, and even steel. It is not the presence of organic materials that causes mold problems, it is the improper management of moisture and humidity in a building that can lead to a variety of problems, only one of which is mold growth.
Generally, mold needs three things to grow: mold spores; moisture; and a food source, which can be as simple as household dust. Mold spores are ubiquitous; they always are present in the air and in the environment. Likewise, buildings are constructed and furnished using a wide variety of organic materials that can serve as a food source. Consequently, the only effective strategy to control mold is to manage moisture.
To minimize the likelihood of condensation developing in occupied structures, the indoor relative humidity should be maintained at a level between 30 and 60 percent. Make sure to vent bathrooms, dryers, and other moisture-generating sources to the outside, and also employ air conditioners and dehumidifiers.
Although insulating the exterior walls, roof, ducts, and pipes is essential to energy efficiency, these surfaces can develop mold if precautions aren’t taken during installation. To reduce the potential for condensation on cold surfaces, it is important to build in a well-sealed air barrier and a vapor retarder on the warm, interior side of a wall or roof to block airborne moisture intrusion.
In the event of water intrusion, clean and dry building materials and furnishings that become damp or wet within 48 hours to prevent mold growth. Clean mold off hard surfaces with water and detergent, then dry the surfaces completely. Be aware, however, that absorbent materials such as carpet and padding that become moldy may need to be replaced.
There has been a great deal of interest in mold-resistant products in the past few years. Although there are many such products available, they should not be considered a miracle cure that will prevent mold in all circumstances. Mold-resistant products, which include certain gypsum panels and mold- and moisture-resistant wallboard, provide added robustness to help when unwanted moisture enters a building. This added level of protection in the event of water intrusion, minor flood, or spillage ultimately will fail if the products are continually exposed to moisture. So, think of mold-resistant products as an extra insurance policy, rather than a primary line of defense. They are not a substitute for suitable moisture management design, proper building practices, and good maintenance.
Only “clean room” technologies, typically used in high-tech manufacturing and scientific research facilities for highly specialized applications such as microchip manufacturing, can completely eliminate mold spores from a room. These technologies tightly control the level of pollutants—such as dust, airborne microbes, aerosol particles, and chemical vapors—but they also are too expensive and too impractical for the vast majority of buildings in which people live and work. In the majority of cases, the primary defense against mold growth is to control the amount of water that enters the building.
Other Potential Problems
Unfortunately, moisture intrusion represents more than the threat of a mold outbreak in a building. A damp environment also fosters the growth of dust mites and bacteria, which in turn can affect IAQ, as well as attract insects, rodents, and other pests. Moisture eventually will damage finishes, as well as make a building less valuable and shorten its useful life. All of this means it is important to treat excessive water with the same sense of urgency as one would a smoldering fire. Immediately identify where the water is coming from, stop it, and dry or replace any materials that are damp.
Be familiar with some of the telltale signs of mold, including dampness, odors, discoloration, peeling paint, condensation, and compacted insulation. A seasonal inspection of an attic will show whether or not blown-in insulation has been compromised by moisture, and discoloration at the top of walls may be an early indication of settling or the absence of insulation in the wall cavity. Certified home inspectors have a variety of techniques to verify this, ranging from probing inside the cavity to thermographic analysis using an infrared camera.
A good guideline is to conduct a quarterly inspection of all spaces within the building to look for the presence of water. If any signs of moisture are detected, make sure to determine where the water is coming from and where it is going. Take steps to stop the water intrusion, and once the site is dry, evaluate whether any building materials need to be replaced.
A dry building not only prevents mold outbreaks, but also creates a more pleasant, healthy environment. A dry building also is more durable and has fewer maintenance problems. Controlling moisture is truly a win-win situation for construction professionals, owners, and occupants alike.
Bob Ek is on the technical committee and board of directors for the Chicago-based Responsible Solutions to Mold Coalition. He can be reached at firstname.lastname@example.org.