Blame Moisture, Not Airtight Construction

Re: "Rising mold-related costs bedevil building industry" June 28. The article’s author attributes current mold problems to newer, tighter buildings. The article further seems to imply that opening windows to provide more ventilation would be a fix for mold problems.

I disagree that tight buildings are a major cause for mold. And, opening windows could make the problem worse.

As an indoor air-quality investigator with over 25 years’ experience, I have had my share of mold investigations. In most cases, moisture problems are directly related to poor construction or building components, or to the failure of a building system, such as plumbing or a roof. Just today, I visited a client with windows that allowed water to enter the walls.

I routinely visit buildings that have had pipes break, roofs leak, sump pumps fail, etc., that allow moisture into buildings. Tightness of a building does not have a direct correlation to moisture problems or mold growth.

Conversely, in humid areas of the United States, outdoor air is a major contributor to moisture in buildings. Opening windows allows this moist air to enter the building. Increasing ventilation also pulls moist air into the building. A person must reason that if mold can grow well in the humid conditions outdoors, wouldn’t it grow well if those conditions are replicated indoors?

Air conditioning systems are charged with removing moisture from buildings. However, air conditioning systems only have a certain capacity for removing moisture. Bringing in more outside air can overtax the air conditioning system, increasing humidity levels indoors. On the other hand, oversizing air conditioning systems, to anticipate such loads, could lead to high humidity conditions under partial-load conditions.

Dehumidifying can help: While building codes do lag the current recommendations, current recommendations tend to look toward the future while building codes must account for the past. Simply changing codes is not always the answer — overall impact of code changes on existing structures must be accounted for as well as future construction.

Augmenting air conditioning systems with dehumidification to account for added moisture loads is a potential answer. In fact, one of my usual recommendations to persons with moisture problems in basements is to use a dehumidifier that is outfitted to constantly drain the sump. In some cases, a simple dehumidifier can arrest mold growth.

But dehumidification systems always have an energy cost. Adding dehumidification systems onto air handlers is in its infancy in the residential market. Until homeowners understand the advantage of dehumidification and start demanding such systems, it will stay that way.

The point is, control moisture: The fact is, tight buildings prevent the introduction of moisture from outdoors that could lead to mold growth. Intermittent moisture added to the environments of such buildings could easily be handled by a properly sized air conditioning system, if the fan in such systems is allowed to operate continuously (they are rarely set to operate continuously).

Tight buildings further help prevent the infiltration of outdoor mold particles, reducing their indoor concentrations. But tight buildings will trap mold contaminants if an indoor mold source exists.

And that is the gist of the topic — control should be focused on moisture to prevent mold growth. It should not be focused on ventilation to dilute contaminants from indoor mold sources.

Ventilation should be used for other contaminants that are byproducts of our living in buildings. But ventilation has to be balanced with the impact it could have on indoor moisture levels.