Our Deep Energy Retrofit project in Lexington managed to beat the air sealing target prescribed by the National Grid utility pilot program; thereby qualifying the clients for an additional $2000 in incentives. We achieved an enclosure air leakage rate of less than 0.1 CFM per square foot of building enclosure.
This project included adding dormers to the second floor in addition to super-insulation. The ability to re-frame and re-roof the building made a tremendous difference to eliminate thermal bridging and wrap the building tightly.
The existing sunroom was not remodeled, so we utilized a technique called the chainsaw retrofit, which entails cutting the overhangs off to be flush with the wall framing; continuous exterior insulation to eliminate thermal bridging and then reconstruction of the overhangs outside the insulation.
Another interesting aspect of this project was the judicious use of spray foam and the generous use of cellulose.To achieve the R-20 walls, we filled the existing 4″ cavity with dense-pack cellulose and 4″ polyiso foam board on the exterior of the sheathing. To achieve an R-60 in the roof, we applied a 3″ flash coat of spray foam on the underside of the roof deck and filled all the rafters (12″) with cellulose. While some spray-can foam was used to fill voids and gaps, the real show stopper was the Pro-Clima joint sealing tape. Lesson learned: in the battle for a tight envelope, air superiority is won with the use of high performance tape.