A collection of experts working on deep-energy retrofits recently attended a brainstorming session to share design tips and propose topics for further research.
The conference, formally titled the “Expert Meeting for Details for Deep Energy Retrofits,” was held in Boston on March 12. The meeting was funded by the Department of Energy’s Building America program and hosted by the Building Science Corporation.
Several experts — including two principals of the Building Science Corporation, John Straube and Joe Lstiburek — gave presentations. Straube discussed retrofit options for walls; Lstiburek covered roofs; and their colleague Kohta Ueno discussed basements. Paul Eldrenkamp, a remodeler from Newton, Mass., shared his experience with several deep-energy retrofit projects, while energy consultant Marc Rosenbaum shared questions designed to stimulate new approaches to reducing residential energy use.
I’ve mined the published report of the proceedings for the following tips and pithy quotes.
If you’re adding rigid foam to your wall, put it on the exterior
Dr. Straube noted the advantages of exterior over interior wall foam. Thick walls without exterior foam usually have cold OSB sheathing. That’s bad: cold OSB is a potential condensing surface — and damp OSB can rot fast. (By encouraging drying, a ventilated air gap between the OSB and the siding can go a long ways toward reducing the risks associated with cold OSB. But adding exterior foam is the best way to eliminate the risk of condensation.)
Among Dr. Straube’s points:
After his presentation, Straube answered questions.
Q: “Can a Larsen truss exterior wall assembly filled with cellulose insulation be used to provide significant insulation to the exterior of a structure?”
Straube’s response: “With a Larsen truss, cellulose, and sheathing on the outside, the sheathing is actually colder than ambient air because of radiation transfer.” (Straube was referring to nighttime radiation transfer,…