This site features research performed by Steven Winter Associates, Inc. (SWA), the lead team member of the Consortium for Advanced Residential Buildings (CARB). CARB is one of six residential research teams that is funded through the Department of Energy’s (DOE) Building America Program. SWA’s research is focused on systems-integration and new technologies to achieve net-zero energy homes.
As a follow up to an evaluation of the MemBrain vapor retarder system in a CARB home built by Veridian Homes in Wisconsin (see In the News for information on this previous study), CertainTeed wanted to compare the hygrothermal performances of DryRight™ fiberglass batts and kraft-faced fiberglass batts in a south facing wall assembly with a moisture storage cladding material. Twelve Humirel temperature/relative-humidity sensors (six in each bay) have been strategically placed to track moisture movement in each bay.
It is noticeable that in the early stage of the rain wetting, the RH levels within the insulation cavity for both vapor retarder bays did not swing as sharply as usual because the ambient condition of rain showers with continuous high RH (>95% for three days). The benefits of MemBrain are most apparent in this situation. Since the ambient condition is wet, the outdoor sheathing is wet and the only path to avoid moisture build-up is the penetration through the vapor retarder to indoor air, allowing drying to the interior. The graph below demonstrates this result showing that the vapor pressure at the outside sheathing and the insulation cavity of the MemBrain system is much lower than the kraft system. This indicates that the MemBrain system will perform better in humid and rainy areas since it provides the “narrow escape” for moisture to the indoor side.
The overall results
indicate that the relative humidity within the insulation of the test bay with the MemBrain vapor retarder was lower than the test bay with kraft paper facing. Also, when the ambient conditions are very wet for a relatively long time span (several rainy days) with significant wetting to cladding and sheathing assemblies, the MemBrain system can provide a moisture escape path by its variable open-pore structure allowing higher levels of drying to the interior than does standard kraft-faced batts.
For the full report on this project, click here. For additional information please contact Zhipeng Zhong at zhong@swinter.com.
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