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It has been claimed that increasing the energy efficiency of building envelope assemblies can result in reduced resilience to recover from water entry from rain into those assembles. This paper describes a series of simulations conducted to aid in the development of a protocol for water accumulation risk assessment due to repeated entry of water at a defect. Hygrothermal modeling is a useful tool and its use is becoming more prevalent in the construction industry. A large step forward in standardizing the protocols for the use of hygrothermal modeling was the publication of ASHRAE Standard 160: Criteria for Moisture-Control Design Analysis in Buildings. This standard, however, “does not address the design of building components or envelopes to resist liquid water leakage from sources such as rainwater, ground water, flooding, or ice dams.” And it “assumes that appropriate measures have been taken to limit bulk water entry into the building and building envelope.” This project used the ASHRAE 160 criteria as a baseline and then imposed upon it a “driving rain defect,” in which a fixed portion of the rain hitting the wall is deposited within the wall assembly. The amount of water deposited and the location of the deposit were varied to understand the wall assembly's ability to handle repeated bulk water leaks. The simulations were conducted on traditional 2 × 4 wood frame wall assemblies and wood frame wall assemblies that have higher insulation levels. The performance of the wall systems were assessed by examining the total moisture content of the wall, the moisture content of oriented strand board (OSB) sheathing within the wall system, and the surface relative humidity of the OSB. The simulation results were analyzed with the goal of suggesting a protocol that could be used to compare the risk associated with repeated small levels of water entry into wall systems.
wall assemblies, water management, hygrothermal simulation
Weston, Theresa A.
DuPont Building Innovations, Richmond, VA