A study for architects, specifiers and engineers found that in three diverse climates, EIFS with a vapor permeable Class III retarder, kept interior wall cavities warm even in the coldest months, thus preventing the possibility of condensation in the exterior sheathing.
Conducted in partnership with the Oak Ridge National Laboratory, the study measured the moisture performance of four EIFS wall configurations: EIFS with either 2-inch or 4-inch of EPS insulation board and a 4-millimeter polyethylene vapor retarder and EIFS with either 2-inch or 4-inch of EPS insulation board without the polyethylene vapor retarder. Researchers reached their conclusions after evaluating framed walls clad with EIFS without stud cavity insulation in three diverse climates (Boston, Seattle and Minneapolis).
The study’s methodology, approach and observations are outlined in a white paper entitled, “Evaluation of the Moisture Performance of EIFS Walls Without Interior Vapor Barriers” published by Dryvit Systems Inc. To read the white paper, visit http://tinyurl.com/4q88639.
Researchers discovered that for the assemblies and climates tested, EIFS’ monolithic exterior insulation properties eliminated the need for a polyethylene vapor retarder to prevent water condensation in a wall cavity. For the three climates investigated, results of the hygrothermal analysis indicate that use of a vapor permeable (IBC and IRC Class III) retarder on the outside face of the exterior sheathing outperforms the use of polyethylene (IBC and IRC Class I) retarder for diffusion control.
“The results show that the EIFS walls with the Class III vapor retarder and without the 4-mil polyethylene vapor retarder dried faster and maintain balanced conditions throughout the year,” said Bill Preston, Dryvit’s senior engineer/code specialist. “It is also clear that a vapor retarder is not required to prevent water condensation in the wall cavity for the assemblies and climates tested.”
Dryvit Study Supports Class III Vapor Retarder as Suitable for EIFS
March 1, 2011