This is the ninth 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).

building envelope design and HVAC systemIt may be only a slight overstatement to state that there is no wall system which a creative architect can envision that a poor HVAC system cannot destroy. Conversely, a very well-performing HVAC system can often compensate for a marginally designed (or constructed) building envelope to the point where many moisture problems may never be noticed. However, there is a point where even an exceptionally well-performing HVAC system cannot compensate for a poorly designed wall system, especially a wall that allows rainwater intrusion or is excessively leaky to air movement.

A simplification of the above concept can be stated as:

  • Bad Envelope Design + Bad HVAC Design = Guaranteed Moisture Problems
  • Good Envelope Design + Bad HVAC Design = Likely Moisture Problems
  • Bad Envelope Design + Good HVAC Design = Likely Moisture Problems
  • Good Envelope Design + Good HVAC Design = Likely Success

(Note: The term “Good Envelope Design” refers to the correct design and construction of the air barrier, vapor retarder, thermal barrier. It does not refer to rainwater intrusion issues since even minor rainwater entry past the water-resistive barrier can be problematic. “Good HVAC Design” refers to the proper building pressurization for the specific climate, proper dehumidification, and proper air distribution within a building.)

Although new wall system products are often intended to provide better thermal insulation, reduce air movement through the walls, or allow enhanced drying of the wall assembly (via vapor diffusion), they can also perform in unanticipated ways. These new products can dramatically change the way moisture flows through wall and roof systems and the potential for condensation within these cavities.

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 d.odom@libertybuilding.com.

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 r.scott@libertybuilding.com.

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 g.dubose@libertybuilding.com.