Four faculty houses built by Unity Homes will set a new standard.
By George Harvey
Unity Homes is building four faculty homes at Dartmouth College to an energy standard requiring very high efficiency. Each will house one faculty member’s household, but the houses are intended to serve multiple functions. They are designed as places for small groups of students and faculty to meet.
On-site construction was begun in late February and early March. The houses have gone up quickly, and faculty members are expected to move in this summer. The rapid pace is actually rather easy to maintain, because the houses are built from elements that are prefabricated at Unity Homes’ manufacturing plant in Walpole, New Hampshire. They can be built to exceptional dimensional accuracy because they are made indoors, in a much more controlled environment than is typical with ordinary construction.
Unity Homes produces the floors, walls, and roofs of its homes in the form of panels and provides the bathrooms as completed modules or “pods.” The bathroom pods already include many of their components as they arrive at the site. For example, they have Kohler fixtures already installed, including a wall-mounted low-flush toilet, tub, sink, as well as a vanity. The insulation is installed in all of the wall panels, which also contain service cavities for wiring to be put in place.
The basement areas of the buildings have R-15 or better insulation. Cavities in walls are filled with dense-packed cellulose insulation for R-35. The attic floor has sixteen inches of cellulose, bringing it to R-60. All this is complemented with highly efficient triple-glazed windows from Integrity and Marvin, with a 0.25 U factor.
When the panels are assembled, the high precision manufacture pays off by making tight air-sealing relatively easy for Unity Homes’ well-trained crews. This results in homes that typically achieve blower door test results of 0.6 ach50 or less. With that quality of sealing, it is important that they have adequate ventilation, and this is supplied by a Zehnder ComfoAir 550 heat-recovery ventilators with dedicated ventilation ducts. The electric resistance water heater is made by Rheem.
The new faculty homes at Dartmouth are larger than a typical Unity Home, ranging in size from 3,063 to 3,255 square feet. Nevertheless, the heat loads range from 32,600 to 35,100 BTUs per hour. Each house gets a single Mitsubishi ductless mini-split compressor, outdoors, with multiple distribution points indoors.
Wood used for construction is sustainably harvested. The gorgeous beams are Douglass fir from the Pacific Northwest, though other wood is obtained much closer to home. The heavy members are engineered lumber, produced through a process called “glulam,” which creates large structural members from smaller, sustainably-harvested trees, without any requirement to cut old-growth trees, in the case of the structural members in these houses.
Some of the carpentry is also unusual. The engineered-wood floors, for example, are “floating”-type floors because not all pieces of flooring are nailed or otherwise fastened, but yet they are very durable. Wood has such an important place in the Unity Homes that it is even used to finish the basement.
Construction with engineered lumber and floating floors implies the use of resins and binders. The standards in use at Unity Homes require that these not off-gas toxic chemicals, such as formaldehyde. What they do have, however, is a high degree of durability, resistance to rot, and even resistance to fire. As hard as it might be to imagine, the engineered beams used by Unity Homes stand up to fires better than steel beams because they char, while steel can simply melt.
Chemical quality is also addressed in the choice of paints. These homes are being finished with Sherwin Williams low-VOC products.
Unity Homes come in different styles, which can be highly customized, to the point that houses of the same style can look very different. The houses built at Dartmouth College are of the Varm style, named for the Scandinavian farmhouses that inspired them. They are two stories tall with connected garages.
These particular homes are not intended to be fully net-zero in energy use. Nevertheless, they are so energy efficient that they could easily achieve net-zero status by adding on solar photovoltaics, either at the homes or remotely. We can easily imagine that might happen.
Unity Homes website is unityhomes.com. The telephone number is 603-756-3600.