This is the tenth 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).

problem avoidance

Figure 3.4: Example of the amount of water absorbed by a wall insulation product. This experiment demonstrates that many products intended for wall and roof assemblies can absorb huge amounts of water in spite of their data sheets attesting to the opposite.

The use of new products mandates that the designer implement several additional steps to avoid problems:

  1. Better understand the performance characteristics of these new products. This may require a more rigorous evaluation of these materials than is required with traditional products. As with any product – but more so with new products – the performance answers may not be found in the product data sheets, but may require experiments and mockups to determine their performance. This type of evaluation may be beyond the scope and expertise of the design team – but it should nevertheless be implemented. In Figure 3.4, a new insulation material (marketed for “green” buildings) was able to hold a considerable amount of water despite a data sheet that indicated it was a non-absorptive product. The use of this material in wall cavities could create massive mold problems if there is water leakage through the water resistive barrier since the normal wet-dry cycle cycling will not likely occur.
  2. Analyze the vapor retarder, air barrier, and bulk water retention properties to better understand where the material should be placed, if at all, within the wall system.
  3. Model the wall systems for performance during the early design stages to predict the potential for water vapor transmission through the wall assemblies and potential for condensation to occur. Minimally, this modeling should predict the dew point location and the vapor transmission profile during the most extreme season for the location.
  4. Perform a three-dimensional analysis of rainwater barrier geometry, especially at complex joints and changes in plane.

All other standard good practices for wall system design should continue to be followed whether new or traditional products are used, including:

  • The use of water resistive barriers as the first line of defense,
  • Designing drainage planes to channel water down and out of the envelope,
  • Installing secondary barriers for redundancy,
  • Designing proper flashing and sealant joints.

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.