Last week I entered the NY-GEO Top Job competition, held each year at the annual NY-GEO conference. I presented a project I did in Rhinebeck, NY. The home was built in 2003 and was recently bought by a couple who wanted to convert the existing heating system to geothermal heating and cooling, and get off of fossil fuel. I helped them convert their home to Zero Net Energy and performed a Deep Energy Retrofit to get them there.
The big challenge was the attic. The second floor of the home projects into the attic, and rather than most of the walls being shared interior ones, they are exterior. The majority of them have the attic on the other side. In addition, the attic floor has many openings that go down into the extensive interstitial spaces formed by tray ceilings and other architectural forms that leave large spaces behind the walls. The interior walls facing the attic were insulated with fiberglass insulation without any backing. Fiberglass and other air open insulation needs to be air sealed on all six sides, or air washing will eliminate most or all of its insulating capability. The exposed fiberglass insulating these walls failed to insulated and might as well have not been there.
The openings in the attic floor allowed cold air from the attic to infiltrate down into the interstitial spaces, cooling them as the cold air displaced the warmer air. This is a huge problem with houses built with tray ceilings and other voids behind the walls and ceilings, known as interstitial spaces. The builder commonly frames these spaces in such a way that they are open to each other, and the attic, since the sheetrock is only on the finished side of the framing. Cold air is heavier than warm air and falls down into these spaces, chilling the sheetrock and adding significant, but hidden, heating loads. Blower door testing will not reveal this problem because the sheetrock traps the air behind itself. Manual J calculations do not take this load into account because it is not expected.
The nonfunctioning insulation and the air bypasses created heating loads that were more than the calculated heating load for the building. The manual J calculations were thus less than half of the actual heating load. The only way to fix these problems was to insulate the roof with closed cell, two pound, spray foam. Had I failed to remedy this situation, this would have been a failed geothermal HVAC retrofit.
The roof was insulated with 6” of closed cell spray foam, with the edges of the roof rafters covered with at least two inches of the foam. This created an intentionally conditioned attic that is air sealed. The owners removed all of the fiberglass insulation from the attic, not wanting the fibers floating around the house. We covered all of the wood in the roof with the foam insulation to eliminate thermal bypasses and prevent micro channels along the rafters that would allow moisture to migrate to the sheathing.
The basement is the other place we did DER improvements. A two inch layer of Dow Thermax insulation was installed directly onto the concrete basement walls. Thermax is the only foam insulation that is listed as a finished wall product and can be left exposed. It has a vinyl off white covering which provides an acceptable, easy to clean surface. The rim joist was insulated with three inches of closed cell spray foam to air seal and insulate this important area. The existing fiberglass insulation in the rim joist did neither.
Due to the relative newness of the windows and exterior cladding, bricks and stucco, we left the walls alone. There was not enough value to justify spending the time and money on these. In the future, when the windows wear out, they can be replaced. The energy savings from the work we did are more than 60%. The testing and energy evaluations done did not fully reflect these savings because the software does not take the poorly performing insulation and the interstitial thermal bypasses into account. It was my knowledge of how these components actually work that made the need for and the value of these improvements clear.
If you go to the power point presentation I made at the NY-GEO conference you will find more information on the project. It also has information on the geothermal HVAC system and the solar PV system that complete the Zero Net Energy Solution.