The methodology of risk analysis and assessment is reviewed and applied to study the reliability of condensation control measures in lightweight building envelopes. It is generally recognized that airtight construction is an essential part of condensation control. Nowadays, different air barrier systems are developed and documented to prevent air leakage and moisture accumulation in the envelope. But does this mean that the condensation risk is sufficiently minimized and that the protective system is reliable? Considering the high occurrence of human error in the building process, the possibility of air barrier defects during the service life of a building envelope may be high. To define the reliability of the condensation control system, the consequences of air barrier failure are quantified using a two-dimensional numerical control volume model for the calculation of combined heat, air, and vapor transfer in multilayered building envelope parts. A set of failure modes and design calculation conditions is defined for an exemplary wood frame insulated roof, and a failure effect analysis is performed in order to predict the condensation risk as a result of air barrier defects. The effectiveness of redundant design measures to improve the reliability of the condensation control system is studied.

AUTHOR: Arnold Janssens, Ph.D., Hugo Hens, Ph.D.
CITATION: Thermal Performance of the Exterior Envelopes of Buildings VII
KEYWORDS: December, Florida, 1998
YEAR: 1998