Super Energy Efficient, Custom Net Zero Home
This new 3 bedroom, 2 1/2 bath home we built in 2013 for a young energy conscious family brought together all of the best elements that can go into a net zero, high performance, super energy efficient home in Vermont; double wall framing, simple, cozy and efficient design, heat pump heat, cooling and hot water, plentiful natural light through beautiful tilt and turn triple pane windows, thermal mass in the floor of the main living space, natural, renewable materials and efficient air exchange heat recovery ventilation and a full array of Solar PV’s on the roof. We took the best of what we had learned on previous high performance projects and applied them to this project and another, similar home we built concurrently that year (see Another High Performance Home in Vermont).
Super Energy Efficient Foundation
We started this home by insulating under and around the footings with 4 inches of EPS foam so the home would have minimal thermal bridges from the ground all the way to the roof. We built our own foundation out of insulated concrete forms (ICF’s) and poured our own concrete walls. This gave us a super energy efficient full basement with R-30 walls with a 6 inch rebar re-enforced concrete core insulated on both sides. The rim joist of the floor system is also insulated on both sides with 2 inches of EPS set in the same plane as the ICF’s and then added 4 inches of air sealed polyisocyanurate foam board on the inside. The inside is finished with drywall which is screwed directly into plastic ties inside the ICF’s and finished on the outside with a fiberglass mesh re-enforced stucco/parging product called Sider-Crete.
We used a typical double 2×4 wall framing system for the exterior walls with a total depth of 12 inches (R-42 insulated with dense pack cellulose). We placed the second floor framing on the inside 2×4 wall so that we could completely dense pack around the rim joist and eliminate the typical air leakage and low R- value issue that plague conventionally framed homes. We used regular roof trusses designed for a flat ceiling with 18 inch raised heels to allow for ample insulation over the top plates of the walls. Ceiling R- value is 85 with 24 inches of loose fill cellulose. When we set the trusses, we continued our 1/2 inch exterior zip wall sheathing up to the trusses, then under the trusses and across the entire ceiling. This enabled us to air seal the entire second floor ceiling before any interior partitions were built eliminating all the air leakage that is typically associated with interior walls and attics. Because of the level of air sealing and high R- value of the attic insulation, we elected not to vent the attic with soffit vents but instead placed simple gable end vents and an exterior attic hatch in one gable end to access the attic space from the outside eliminating interior access and further air leakage.
We used Schuco triple pane tilt and turn windows (Passiv Haus certified) that have impressive performance values. U factors on the south side are U- 0.16 with SHGC of 0.62 and on the east, west and north sides we went with a lower U-factor (higher R-value) of 0.14 with a lower SHGC.
This house has a standing seam metal roof, pretreated red cedar siding and painted Miratec trim. The soffits are tongue and groove pine and we used some vertical ship lap pine on the upper parts of the gable ends. The covered entry porch and screened in porch at the other end of the house were built post and beam style with local Hemlock beams, white pine ceilings and red cedar deck flooring. We built our own custom screening systems also out of red cedar and fiberglass mesh. The inside features an aggregate ground 3″ concrete floor in the front half of the first floor and mudroom and red birch floors in the kitchen and hallway. The second floor has white pine floors throughout all the bedrooms and Marmoleum in the master and kids bathrooms. The master bath has a separate soaking tub and large shower. White pine trim was used for baseboards and door trim, maple for the window sills. The windows are all wrapped in drywall on 3 sides. The kitchen features painted solid hardwood ply cabinets and Vermont Slate counter tops and a big pantry with custom built in pine shelving. No VOC California paint was used on the walls and ceilings.
Mechanicals- Heat Pump Hot Water Heater, Air Exchange Heat Recovery Ventilator, Solar Electricity
For heating and cooling, we used a Mitsubishi FE-18 hyper heat mini split centrally located in the main living area. The house also has a small wood burning stove for those really cold winter days. Hot water is provided by a State 60 gallon Heat Pump Hot Water Heater. Heat Recovery Ventilation is a ducted, whole house Zehnder 350 air exchange heat recovery system. We did install a soil heat exchange loop around the base of the footings so that a heat exchanger can be added to the Zehnder at another time to provide further pre warmed and pre cooled air. Exhaust ports were placed in all the bathrooms and kitchen and fresh air supplies placed in all the bedrooms and living spaces.
Many people ask about building costs. This home ran about $190/ square foot from the foundation work on up. Site work, septic, land and solar are not included in that cost. The other home we built during this same time was built on a frost wall protected slab and was closer to $185 per square foot. These costs also do not include costs for the design phase of the project.