This is the thirteenth post in a series by J. David Odom (ASHRAE), Richard Scott (AIA/NCARB/LEED AP), and George H. DuBose (CGC). It was first published as a mini-monograph for NCARB (National Council of Architectural Registration Boards).

the "golden rule" of moisture controlThe HVAC system that introduces ventilation air must also do so in a manner that properly dehumidifies the air. The “golden rule” of moisture control is that under no circumstances should adequate dehumidification be sacrificed for increased ventilation. In many regions of the country during summertime conditions, the moisture load contributed by the outside air can exceed the amount of moisture that the air-conditioning system can effectively remove.

The solution is to address these risk factors in several ways:

  • Insure the correct distribution of air flows within buildings (to avoid pressure imbalances). This can usually be accurately predicted during design.
  • Increase the verification of HVAC system performance by adding additional elements to the building start-up and commissioning programs. This post-construction verification includes detailed pressure mapping of the building to confirm proper air distribution and using temperature and relative humidity (RH) data-loggers to confirm conditions during the first year’s operation. This pressure mapping and data logging needs to also include the building cavities – areas that are often ignored. Many of these elements are frequently absent in today’s standard HVAC system start-up and building commissioning programs.

What experience demonstrates is that increased amounts of outside air can be safely added to a building if the known causes of increased risk (such as proper air distribution) are addressed during design and verified after construction.

To be continued…

J. David Odom is a Vice President and Senior Building Forensics Consultant with Liberty Building Forensics Group. He has managed some of the largest and most complex mold and moisture problems in the country, including the $60M construction defect claim at the Hilton Hawaiian Village in Honolulu and the $20M claim at the Martin County courthouse. He has also managed over 500 projects for the Walt Disney Corporation dating back to 1982 that have included technical issues related to corrosion, moisture, and design & construction defect-related problems. He has published numerous manuals and technical articles, including a monograph on moisture and mold for the National Council of Architectural Registration Boards (NCARB). For more information, contact J. David Odom at

With over 35 years of experience, Richard S. Scott is an expert in the areas of architecture, interior design, and building forensics, with a focus on moisture-related building problems. He is certified by both the American Institute of Architects/AIA Florida and the National Council of Architectural Registration Boards (NCARB). He has published over 30 articles, and has lectured or presented at nearly 40 seminars or events. Mr. Scott has developed various training courses, including a 16-hour IAQ training course for NASA and an 8-hour water intrusion prevention training course for the Naval Facilities Engineering Command (NAVFAC). He can be reached at

George H. DuBose, CGC is a certified Florida General Contractor and Vice President with Liberty Building Forensics Group, a firm specializing in moisture intrusion, mold problems, litigation support/buildings forensics, problem-avoidance peer reviews, commissioning, and implementation of green buildings. He has authored numerous articles and co-authored three manuals on moisture-related indoor air quality (IAQ) problems and building commissioning. He has diagnosed and solved hundreds of moisture and mold related building problems worldwide. DuBose can be contacted at