High Performance, Hyper Energy Efficient Home
High Performance in the Hills of Vermont
We had a lot of fun building this super insulated, high performance, hyper energy efficient home in 2012. Many unique design features both inside and out were incorporated into the construction many of which were designed by the owners Lisa and James themselves, so we developed a very close, collaborative relationship with them. The home presented some interesting challenges. The first was hitting ledge only 18 inches down when we started excavating, so we had to completely redesign the foundation. Ultimately, we elected to build a super insulated floating or Alaskan slab which has no frost walls. Instead of pinning the frost walls to the ledge, which would have created a huge thermal bridge, the Alaskan slab allowed us to create a foundation fully insulated from the ground with no thermal bridging, an important standard in high performance, hyper energy efficient homes.
We used 8 inches of high density EPS foam board (two layers of 4″) to insulate under the slab and 6 inches along the slab edge to fully encapsulate the slab and eliminate thermal bridging. The foam panels were used as the concrete forms and were set up so that the edge of the slab was 12 inches in thickness while the rest of the main slab was 5″. All plumbing and wiring conduit was roughed in before pouring the concrete.
We framed the house using a double 2×4 stud wall technique used on many super insulated homes. This creates a 12 inch thick wall cavity with a 5 inch space between the walls creating a substantial thermal break between the inner and outer walls. We used Igloo dense pack cellulose, our favorite insulation material, to insulate the walls. We designed the roof trusses with 18 inch raised heels to ensure the thick insulation was continuous from bottom plate to top plate and created a 20 inch deep cavity in the trusses so we could super insulate to R-70 all the way to the roof peak. This also created some attic space inside the thermal envelope for storage and the air exchange, heat recovery ventilation system.
The owners wanted the house to have a post and beam look to it to match their barn. Because we used conventional engineered roof trusses, we elected to add custom milled rafter tails which we bolted to the trusses. Tongue and groove pine was run over the top of these to create a soffit. Since the rafter tails penetrate through the exterior sheathing of the house which is the air barrier, we air sealed these penetrations with 2 part spray foam from the inside. This can also be done with special European air sealing tapes which are now (2014) more readily available.
The outside of the house was finished with locally milled ship lap pine which the owners coated themselves ahead of time in drying racks we built for them. Exterior trim was minimal with thin corner boards and only extension jams around the windows which the ship lap butt into creating a simple, clean look. We built a small post and beam covered entry porch and deck and installed a long ledger along the south facing side of the house to accept a future Pergola over a large deck.
Inside, the kitchen was put together by a local cabinet maker and built to the owners specifications. Simple, clean lines were the theme throughout the house from the custom maple ply closet doors to the built in shelves beneath the stairs (which is the home for the air source heat pump which heats and cools the house). There were many other custom finishes including a number of built in shelf units, custom joined window sills made from 8/4 reclaimed pine, maple trim that was harvested off the owners land years before, a site built custom wrought iron stair railing system, and custom stairs made from reclaimed wood as well. The windows we used were from Intus- triple pane, super insulated glass with wood frames from Europe. These were finished by the owners using different types of stains and finishes depending on the room they were in. Upstairs we installed some reclaimed wide pine floors and Oak.
Heat Pumps, Air Exchange Heat Recovery Ventilator, Solar Hot Water, Indoor Air Quality
This house is equipped with a Mitsubishi FE-18 air source heat pump which both heats and cools the entire house from a single point in the living room. Because the house is built with such a low energy demand (75% less than a conventionally built home of the same size and design) the heat pump, which is normally used for supplemental heating and cooling, can take care of the entire house.
The house is supplied with regular fresh air which is either pre-warmed or pre-cooled by the exhaust air being pulled out of the house by the German made Zehnder air exchange, heat recovery ventilator specified, supplied and commissioned by a company in Maine. The system is so simple the all the duct work was installed by our crew.
Hot water is supplied via two solar hot water panels on the roof, 80 gallon storage tank and backed up by a standard 50 gallon electric hot water heater.