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| Soy-based closed cell spray foam in exterior walls |
After using advanced framing to maximize the energy efficiency from a structural and framing basis, we selected highly efficient windows and turned our focus on the insulation of the building envelope. The objective is to build a very efficient home and use a solar PV system to minimize the actual purchase of utility power. When focusing on energy efficiency, the absolute most important element in the design of the home is the insulation.
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| Open cell foam under the roof deck |
We attended Greenbuild in 2009 in Phoenix and saw a demo of a hybrid system at the CertainTeed exhibit. Seeing an actual demo structure allowed us to better understand what we were asking of our builder in 2010, and of our insulation subcontractor in 2011. Learning about the envelope and advanced framing also helped us to choose a quality builder who had experience with green building techniques.
Our house is constructed using four different types of insulation:
• Roof deck - 8” of open cell spray foam to achieve R30
• Exterior walls - both closed cell soy-based foam and blown cellulose to achieve R27
• Floor – Fiberglass batts
The house was framed using 24” x 6” on center advanced framing. This means that the framing is 24” apart and the exterior walls are 6” deep to allow for very thorough access during the insulation phase. There is not an exterior surface that is not extremely well insulated. In the walls, we decided to go with a hybrid system that includes 2” of closed cell foam and 4” of blown cellulose. Closed cell foam has many advantages but is extremely expensive compared to open cell foam or cellulose. By using only 2” of the closed cell foam we gain the benefits of a tight seal, added structural rigidity and improved wind resistance for the home. Closed cell foam is made from soy beans and does not allow water or air to pass and it is mold and pest proof. However, when reviewing costs it became evident that 6” of foam does not deliver as much R-Value per dollar as a combination of insulation methods.
Quite a few of the contractors wanted to be involved in a green project, but lacked actual experience. We chose Gai Kirkegaard to build our home because he had already built a LEED Platinum home in our town: he talked the talk and walked the walk. He even drives one of the most efficient cars available-proof that he lives efficiently. When talking about the envelope or advanced framing, Gai and his team truly understand the intricacies of green building.
This week was exciting as both the roof and insulation were installed. The insulation installers make a terrible mess, but as soon as they clean up we can schedule the insulation inspection. After that drywall starts and we can start counting down the weeks until we get to move in. Whoo-hoo!
