By Matthew Power. Because mold remains one of the big scare issues for builders, the NAHB Research Center recently began monitoring and testing new homes with mold problems. The staff chose 21 building sites in various states, including single-family attached and detached, along with three multifamily projects.

In selecting the buildings, the researchers used three criteria: 1. Homes had to have been built within the last five to seven years; 2. Home style and size is fairly typical; 3. Problems found could likely affect other homes.

At the time of this writing, the researchers have investigated about half of the homes and have reached some preliminary conclusions. They note that mold problems can be roughly divided into three categories: building design related, material and construction related, or homeowner related.

The one constant: In every mold case examined, moisture appears to be a factor. A few quick examples: A two-year-old modular home in Virginia with basement mold was traced to a roof downspout discharging at the foundation and an uncovered crawl space. In a six-month-old home in Pennsylvania, mold on rafters was caused by exposure to the elements during construction. And in Delaware, a four-year-old home had mold growing on gypsum walls in two bathrooms. The builder replaced wall components but the mold returned. The walls have vinyl wall covering.

The researchers have yet to make recommendations based on the final report, due out soon. They do offer one tantalizing (and surprising) insight: "Research Center engineers say they have not observed any trends that directly link a home's envelope tightness with the presence of mold."