The Passive House in the Woods is the first certified Passive House project in Wisconsin. Completed in 2010, it delivers monitored net-energy positive (beyond net-zero) performance for all energy consumed on site in this cold western Wisconsin climate zone. The home features a 3-bedroom, 1,940 square foot, two-story layout, a walk-out basement, as well as a rooftop terrace. Located on the outer edge of a residential development, the it overlooks the St. Croix river valley, provides stunning views and prime passive solar exposure.
The Passive House in the Woods is a certified Passive House, which mean it meets—and in fact exceed the most stringent building energy standard in the world. It was designed from the ground up to perform with the client setting a clear target for the design and build team.
The building envelope, which consists of exterior walls, windows, doors, basement slab, and the roof was designed according to Passive House principles to radically reduce the amount of energy used to condition the building. The exterior wall assembly of the Passive House in the Woods consists of 11” thick Insulated Concrete Forms (ICF) for structure, and an additional 11” thick Exterior Insulation and Finish System (EIFS) facade with an overall R-value of 70—about 3.5 times the code-required amount. Windows and exterior doors are Passive House certified, come with a very high solar heat gain coefficient (64%), triple pane low-E coated glazing, as well as insulated frames for installed R-values of 8. The basement slab rests on 12” of extruded polystyrene insulation with an R-value of 60. The flat roof utilizes an average of 14” of polyisocyanurate insulation with an R-value of 95, which compares to the code-required R-38. The highly insulating assemblies of the building envelope are commonly referred to as super-insulation. Performance is further enhanced by the fact that the home is extremely airtight, measuring only 64 CFM of air leakage at 50 Pascals pressure, or 0.25 ACH50. This make Passive House in the Woods one of the tightest buildings in North America.
The mechanical system in a Passive House is typically centered around a heat-recovery ventilation system. In milder climates, this system provides all the necessary heating energy, as well as outside air needed for balanced, hygienic ventilation, and therefore superb indoor air quality. The heat-recovery ventilation system in the Passive House in the Woods consists of a high efficiency heat-recovery ventilator, a home-run tube distribution system as well as a ground-source heat exchanger made from 600 feet of PEX-tubing, which are buried well below frost on the property. This “earthloop” pre-heats and pre-cools/ dehumidifies the fresh air supply to the home and therefore becomes a “passive” air conditioner.
In extremely cold climates, the Passive House paradigm of heating the fresh air supply changes slightly. While the overall annual energy goals for a Passive House can easily be met, the extremely cold peak winter temperatures call for a small additional heat source. At the Passive House in the Woods, electric in-floor heating mats with local room-air thermostats were installed to provide the 3 kW or 10 kBtu required for the job. That compares to the energy draw of two hair-dryers to heat the entire home on the coldest day of the year. There is not a boiler, or furnace in this house.
Renewable energy systems are optional and not required by the Passive House standard. Our client chose to achieve a net-energy-positive energy balance. A 4.7 kW photovoltaic system generates an annual surplus over the energy consumed on site, avoiding approximately 2.78 tons of CO2 annually.
The domestic hot water system utilizes a 40 square foot hot water solar collector on the roof to pre-warm water in a 50 gallon storage tank. It is capable of providing over 85% of the hot water used in the home. Backup water heating is provided by a small electric on-demand water heater.
In addition to the performance, we also paid a lot of attention to detail—both outside and inside. The use of natural and durable materials helps with graceful aging.
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. The style was dubbed “warm modern”.
The Passive House in the Woods broke ground on December 3, 2009 and the project was completed in September of 2010.