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.”