2016 Challenge Participant:

Northwest Builders/CK Architects - Post Residence

Applicant: John Post

Project Address: 159 Old Mt Tom Rd, Bantam, CT 06750

Bdrms./Sq. Footage: TBD

Builder Websites: www.northwestbuildersltd.com, www.ck-architects.com

Project Overview Project Specifications Project Team Project Photos
The Northwest Builders/CK Architects - Post Residence project in Bantam, CT.

General project overview:

The property was designed as a working farm with a compact main house, a detached garage/workshop and a separate barn that is used to store equipment and supplies.  The three buildings are composed on the site to shape a traditional yard and to help frame the sweeping views of the surrounding valleys below.  We clustered the buildings on the west side of the site, leaving much of the existing meadow area available for farming.  Driven by the desire for the new home to feel comfortable within the area’s historic New England farmhouses, we used an efficient, one and a half story main volume, similar to the historic Cape style homes in the area.

Special Features:

  • Due to high ledge conditions and our interest in avoiding the environmental impacts of blasting, we designed the home on a super insulated slab-on-grade foundation that was pinned to the ledge.  This made for an extremely tight and well insulated foundation, minimizing the heat loss and air infiltration challenges associated with a traditional basement system.   

Orientation and Envelope: (windows, insulation, framing)

  • The new home is placed at the high point of the site which allows for sweeping views as well as a natural breeze that helps with cooling.  The back of the home holds the major living spaces and opens up to the south allowing ample area for well oriented PV, natural light and good solar access. The front of the home, which faces north, has more traditional, smaller-scale punctured windows, designed to minimize loss, while allowing plenty of natural light and views to these secondary spaces. 

  • We used a slab on grade floor system with a structural slab floated on 4” of XPS foam with 2” at the perimeter of the slab.  We then have an additional 1 ½” of XPS foam over the slab and secured with two layers of ½” plywood run in opposite directions and fastened with split anchor fasteners.  This makes for an extremely tight floor system that has total continuous insulation value of R-30 and no thermal bridging.  We used 2x6 wall framing with raised headers and open-cell spray foam cavity insulation.  The exterior is sheathed with the Zip system which provides the primary air barrier.  To the outboard of the sheathing we installed two 1 ½” layers of XPS rigid foam, secured by rainscreen strapping then cement plank siding and CPVC trim.  This system gave us R-20 cavity insulation plus R-15 continuous insulation outboard of the sheathing for a total system value of R-35.  The roof system is composed of 2x12 rafters, with 4” of closed cell under the deck and 7” inches of open cell to fill the cavities making an unvented system that minimizes the risk of internal condensation issues in this climate zone. The roof system provided a tight R-52 insulation value.

  • For the windows, we used Windsor Legend Hybrid units, double hung in most locations, in order to maintain a historic appearance. These units have a low-e, argon fill that achieved a U value of .29 and a SHGC value of .2. When modeling the envelope in REM Design, the ROI for triple glazing units proved to be minimal in our system and we elected to invest in additional air sealing and insulation which showed a much faster return.  Through careful taping of all seams and penetrations and the tight nature of the double glazed windows, we achieved an air infiltration value of 0.37 ACH50 with this mid-grade window, giving us a very tight interior environment. 

Heating, Cooling, and Hot Water:

  • Waterfurnace Series 7 geothermal system to heat and cool the home. The unit is 3 tons with an ECM variable-speed fan and variable-speed scroll compressor.
  • The unit and all associated ductwork is in the second floor for the home, completely within the thermal envelope.  The system serves the first floor from above with no need to penetrate the slab. 
  • For the domestic hot water, we used a desuperheater on the geothermal with a 30 gal storage tank feeding a Noritz on demand LPG modulating water heater.  We utilized a manually-activated recirculation loop and mini storage tank to minimize wait times on the major faucets.  Given the proposed low occupancy of the home, we feel that the desuperheater will provide more than 70% of the domestic hot water needs, calling on the propane on-demand system only occasionally during the shoulder months when the geothermal system is not running.
  • To minimize equipment, we also are using the on demand water heater as the geothermal backup heat source through a heat exchanger and a coil in the air handler.  We have utilized this set up on many homes and found it to achieve very high performance. 

Ventilation:

  • With the extremely tight envelope and high insulation values, the design necessitated a balanced ventilation system.  We used a centralized Venmar Energy Recovery Ventilator (ERV) system that exhausts air from the bathroom spaces on each level and introduces fresh air through the HVAC system into the sleeping areas.  This system continuously exchanges air with the outside to the ASHRAE recommended levels and can be adjusted based on occupancy and humidity levels in the home.  The system is able to recover about 80% of the energy from the outgoing air into the incoming air, minimizing the loss of heating or cooling energy in the exchange.  

  • The operable double-hung windows are set up to capture the prevailing summer breezes and maximize the cross ventilation in the main living spaces.  Natural ventilation will only be utilized when exterior condition are conducive and will not introduce excess humidity, pollen and dust into the home.  Because the geothermal systems are so efficient and the envelope is so tight, in most cases the active geothermal systems will be more efficient in maintaining a healthy indoor environment than natural ventilation would.

  • We separated the three major uses of the property into three distinct detached buildings to minimize pollutant migration and fire risk.  The garage is separated from the main house by about 8 ft in order to avoid the risk of hydrocarbon pollutants migrating into the home.  The barn is located down wind and down slope from the home to minimize odors and the risk of fire.

  • The on-demand water heater is a fully sealed combustion and there is no fireplace in the design, avoiding all hydrocarbon usage within the home.

Electrical:

  • Conventional recessed cans with LED light trims are installed in locations that do not penetrate the air barrier or compromise the insulation depth.  All fixtures can accommodate common available LED bulbs, including the LED under cabinet lighting in the kitchen. We took a very simple strategy to the lighting controls and light levels throughout the home.  The general light levels are set for comfortable occupancy, but we rely on furniture and task lamps to achieve reading levels in the living room, office and bedroom spaces.  In practice, we feel this will reduce the watts per square foot used by the occupant. 

  • In order to fully leverage the onsite renewable energy opportunities, all major systems are designed to be electrically powered.  The 9.81 KW PV array is sized to provide all of the house’s energy needs on an annual basis plus excess capacity for an electric car.  The array is grid tied and will use the utility to store the excess summer generation for winter heating, lighting and appliance loads.  Because of its rural location and thus the possibility of long-term power outages, the house is outfitted with a stand by propane generator to allow the house to operate when the grid power is down. 

Renewables:

  • We installed a 9.81 KW photovoltaic array on the south facing dormer roof.  We designed the roof area to provide an ideal orientation and inclination with zero shading for the new array thus maximizing its performance. The PV system, in conjunction with the geothermal heating and cooling, desuperheater hot water production, LED lighting systems and all electrical cooking appliances, is projected to provide all the energy to run the home except for the propane backup systems for the cook top, hot water, heating and emergency electric generator.  The system was sized to provide power for the future use of an electric vehicle which has a charging station in the garage.  

Resources Sustainability Features:

  • The marrying of the housing, barns and farmable land is the most important sustainable feature of this project.  Land stewardship, composting and conservation will rise to an extremely high level in this symbiotic arrangement. 

  • The barn and garage were built by a local kit builder that mills its own pine timber and siding from locally harvested sources. Cement siding and CPVC trim are installed on a rain screen to promote low maintenance and long term durability. We have employed passive insect management techniqu

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