A Home Like No Other
The ARC is a highly experimental residential home built with all the comforts in mind. As Paul Hunt likes to say, “It’s half house, half business and meeting space, half research lab, and half greenhouse.”
AN INSULATED BOX. It uses an insulated concrete form (ICF) foundation made of reinforced concrete, with foam insulation on both sides. The garage and the greenhouse also have “apron” insulation, which is foam extending horizontally from the slab foundations. Ground frost is forced to go around the insulation in order to reach the slab. The house uses a slab floor, which sits on top of 24 inches of sand, which itself is insulated on the bottom with 10 inches of foam insulation. Essentially, it’s a slab of concrete floating in an insulated box of dirt. Backup is in-floor heat, which uses a single electric hot-water heating element as its heat source. In January, the heating element is only needed one or two days a week.
12-INCH THICK WALLS. The walls are made of Structural Insulated Panels or SIPs, constructed from 12 inches of foam insulation with plywood on both sides. The panels are effectively a very strong box beam, so there is no need for a traditional housing frame. The SIP walls have an R-value of 50, while the blown cellulose insulation under the roof is R-100. The insulation under the floor is R-50 and the “apron” insulation extending from the garage and greenhouse is R-20. Together, they create a super-insulated home. During its first winter, the home was left unheated for 2.5 days, with night time temperatures reaching -31 F each night. The inside temperature dropped only slightly, from 75 degrees F to 65 degrees F.
SUPER EFFICIENT WINDOWS. We took advantage of the foot-thick walls by making foot-thick windows. We used two sets of double-pane windows with about 10 inches of dead air space in between. It turns out that two double pane windows cost far less and perform better than a good triple-pane window. At first we weren’t sure whether this was a good idea, but it worked so well we have used it in every building constructed since then.
Hydroponic greenhouse doubles as gray water recycler
The ARC includes two greenhouses or solariums, which for years were used as comfortable sitting areas providing warmth and humidity during a cold dry winter. In 2015 they were converted to become sewage processors of a sort. Up to 300 gallons of gray water a day from washing clothes, dishes, and bodies are captured in a tank, with that water trickling through a series of plants. The hydroponic plants are in a bed of activated charcoal. The gray water trickles through a series of 120 trays, with the plants pulling the impurities from the water and using it as nutrients. By the time it trickles back out after 112 feet of water processing, it is clean and clear. Just to be safe, the water then goes through a purifier before returning for use for drinking, cooking, and cleaning. By opening windows between the house and the greenhouses, the plants also provide the added benefit of humidity, a valuable commodity during a Minnesota winter, while increasing oxygen and cleaning the air.
Gray water passes through more than 100 feet of trays containing plants and activated charcoal.
The 1,000 sq. ft. garage, with its open design, concrete floor, and passive solar wall never freezes in winter even though it has no other heat source and no thermal mass under the floor. .
Garage stays warm all winter with no heat source or thermal mass
The garage itself is often considered a model for an inexpensive single room efficiency home. Because of the passive solar heat and big open-slab floor, the 1,000 sq. ft. garage maintains its heat all winter long. It remains a warm work space, even in January, without any heat source at all. The slab has four feet of apron insulation extending horizontally, which keeps the frost from reaching under the garage. The open passive solar-heated space warms the concrete slab and the earth under it, although there are no tubes or special features transferring heat under the floor. This thermal mass holds the heat and radiates warmth back during the long winter nights. Garage temperatures stay above 50 degrees during winter and hovers in the 80s during the hot part of the summer.