Passive House in the Woods
By the Numbers
|Climate Zone:||6; Cold & Dry / Hot & Humid|
|Size:||1,942 sq. ft. (1,770 sq. ft. TFA)|
|Levels:||B, 1, 2, Rooftop Terrace|
|Walls:||Insulated concrete form 279 mm (11”):
64 mm (2-1/2”) EPS (035),
150 mm (6”) concrete,
64 mm (2-1/2”) EPS (035)
279 mm (11") Sto exterior insulation and finish system (035)
U-value = 0,083 W/(m²K); R-70
|Roof:||EPDM reinforced rubber membrane over 305 mm (12") to 445 mm (17,5") tapered polyisocyanurate insulation boards (023) U-value = 0,06 W/(m²K); R-95|
|Floors:||102 mm (4") concrete slab on top of 304 mm (12") EPS insulation (030) U-value = 0,097 W/(m²K); R-60|
|Mechanicals:||Inno-Products Innoflex home-run flexible ductwork. 600 foot PEX earthloop with Luefta liquid-to-air heat exchanger, summer bypass. Nuheat electric in-floor heating mats with programmable thermostats. Cooling: Earthloop.|
|Windows:||Optiwin Alu2Wood PHI-certified Uw-value = 0,82 W/(m²K); U-0.14 Btu/ (h sf F)|
Holistic Passive House Design
Mattson MacDonald Young
Eric Bunkers, Shannon Pierce, Chris Hartnett
Carol Chaffee & Associates
Laurie McRostie Landscape Architect
The Konkol Residence
The Passive House in the Woods is a 3-bedroom, 1,940 square foot, two-story single-family home with walkout basement level, and a rooftop terrace. Commissioned by a private client, this home is the first certified Passive House in the state of Wisconsin, and at the time of completion one of only 5 Passive Houses in the United States. Located on the outer edge of a residential development, the home overlooks the St. Croix River valley and provides stunning views and prime passive solar exposure. With its renewable energy systems, it is projected to make more energy than it consumes and achieve zeroenergy and carbon-neutral operation with two people. You may find more information about this project at passivehouseinthewoods.com
The client demanded a holistic approach that would deliver on all aspects of sustainability. In addition, the house was to operate carbon neutrally for a household of two. A tight setback line and the desired rooftop terrace reduced the window of opportunity for solar photovoltaic energy generation. This in turn gave the designers an energy allowance to which to design the performance of the home. In response, the building’s glazing was selected to allow a high degree of solar energy to heat the home (SHGC 64%), and the envelope to exceed the Passive House standard criteria. The home’s calculated heating demand is only 11 kWh/ (m2 a).
High-Performance Building Envelope
Exterior walls, windows, doors, slab, and roof designed according to Passive House principles radically reduce the amount of energy used to condition this building. The exterior wall assembly of the Passive House in the Woods consists of 11” Insulated Concrete Forms (ICF) for structure, and an 11” Exterior Insulation and Finish System (EIFS) façade with an overall Rvalue of 70. Windows and doors are Passive House certified, come with high solar heat gain (64%), triple pane low-E coated glazing, as well as insulated frames for installed R-values of 8. The slab sits on 12” of foam insulation with an R-value of 60. The flat roof utilizes an average of 14” of polyisocyanurate insulation with an R-value of 95.
The mechanical system in a Passive House is often built upon a heatrecovery ventilation machine and fresh air distribution throughout the building. In milder climates, this system can provide all the necessary heating energy, as well as outside air needed for balanced hygienic ventilation. The heatrecovery ventilation system in the Passive House in the Woods consists of a Passive House certified high efficiency heatrecovery ventilator, combined with a 600-foot PEX-tubing loop field— buried on the property—to pre-heat and pre-cool the incoming air stream. This also dehumidifies moist summer air. However, it does not provide any “active” heating to the home, which is accomplished by seven individual zones of electric resistance in-floor heating mats with a calculated design heat load of less than 3 kW or 10 kBTU—that is the equivalent of two hair dryers going at the same time, or approximately 90 candles.
Domestic hot water is pre-heated with a solar thermal panel on the roof, and post-heated by a modulating on-demand electric boiler. The plumbing runs in the building are reduced to a minimum, with most connections located in one wall that connects all three floors. All water lines are continuously insulated to provide maximum efficiency and durability to the system. The solar thermal fraction of heat input covers over 85% of the hot water demand for two people in the home.
Renewable Energy, Positive Energy Balance, Carbon Neutrality
Renewable energy systems are optional and not required by the Passive House standard. The client chose to achieve a net energy positive energy balance and carbon neutral operation. A 4.54 kW photovoltaic system generates a surplus over the energy consumed on site, avoiding 2.78 tons of CO2 annually, and therefore providing carbon neutral operation for a household of two people.
Attention to Detail
In addition to the performance, we gave a lot of attention to detail— both outside and inside. The use of natural and durable materials will help graceful aging. One example of this is the extensive use of earthen plaster as a wall covering. This material can be spot repaired, does not off gas, and does not require any painting. Baseboards, windowsills, door trim, wall paneling, and the staircases were fabricated from wood that was harvested on site and responsibly manufactured and finished. We developed an earth-friendly, healthy and durable material palette in cooperation with InUnison Design to blend the client’s priorities of health and performance with his love of the outdoors and nature.
Designing a Passive House in an extreme climate is a fair challenge. During the heating season a heating system is still required— albeit very small. During the cooling season, some means of active cooling and dehumidification are needed. Both items are typically not found in a Passive House. We looked to passive technologies to avoid the use of energy as much as possible. We learned that a high dependency on passive solar heat gains can create a comfort challenge and requires diligent management of the windows, which become heaters. Some thermal mass is also required to absorb, and time-release any excess energy. During periods of low solar heat gains, traditional means of heating need to be in place to provide the necessary energy input into the building envelope. Our office recently completed the first year performance evaluation of the home, which is monitored. We understand the PHPP to calculate a theoretical level of performance— similar to the MPG rating on a car —which does not necessarily represent real-life performance based on user interaction. Having said that, we find that in many aspects, the PHPP calculations were very accurate. Some consumers even beat the predictions. On the flip side, some consumers used more energy than estimated. More years of monitoring are needed to fully evaluate what this means for the overall performance of the home and the validity of the PHPP in an extreme climate such as ours.