Whole-Wall Thermal Performance: Moisture Tolerance
The wall moisture behavior, like the benefit of thermal mass, is a function of climate and building
operation. The likelihood of annual moisture accumulation due to vapor diffusion of a particular
wall system can be estimated by computer simulation. Moisture accumulation due to airflow into
the wall is more difficult. The air pressure equalization effectiveness of any rain/drain screen
inherent in the wall systems can be measured by monitoring the pressure difference across the
rain/drain cavity from the exterior to the inside. One important feature to have in a long- lasting
wall assembly is the ability for the wall to dry itself out if it should be built wet or pick up
moisture due to a leak in the course of its in-service life. The drying rate can be modeled and
measured in the laboratory. The potential for moisture accumulation (an undesirable
characteristic) over specific full annual climatic cycles also can be modeled by heat and mass
transfer codes such as MOIST and
MATCH (Desjarlais et al. 1994). This element will most
likely will be addressed for each system by a modeling activity, except for periodic model
validations by physical experiments conducted in laboratory hot boxes.
For more information, contact the program manager for Building Envelope Research:
André O. Desjarlais
Oak Ridge National Laboratory
P. O. Box 2008, MS 6070
Oak Ridge, TN 37831-6070
E-mail Andre Desjarlais
Revised: May 26, 2004 by Juanita Denton