The 2014 North American Passive House Conference
Last week I attended the North American Passive House Conference in Portland, Maine. The high point for me was the presentation by Peter Schneider of the Vermont Energy Investment Corporation (VEIC) on what they are doing with affordable housing. So much so that I took a day after the conference and drove over to see the factory where Steven Davis and Chet Pasho are building these houses.
I had met Peter several years ago and been inspired by his work in building Vermont’s first Passive House—a modular home for Vermont’s Habitat for Humanity. We were very influenced by that project in the modular Passive House we are now working on with the Housing Initiative Partnership.
The most immovable obstacles we have faced in creating our modular affordable home have been land costs and the on-site construction costs. The cost of the modular home itself ends up being only about 1/3 of the total project cost. Schneider and the VEIC have come up with an approach that solves both the land and the site-finishing problems.
They are addressing land costs by focusing first upon trailer parks, where the most inefficient housing is located. Working in partnership with Efficiency Vermont they are going into mobile home parks and replacing homes in situ with new modules that are net zero and which cost less to own (mortgage + energy) than the homes they replace. The fact that the land is leased, not owned, makes the mortgage much more affordable. And they have worked with appraisers and banks to get the homeowners 30 year terms on these mortgages. They plan to replace all substandard manufactured housing in the state with net zero homes by 2030.
VEIC is addressing the site finishing costs by teaming up with up with VERMOD Homes in Wilder, VT to make houses that owners can move into sometimes on the same day that they are delivered to the site. Everything is done in the factory. These houses can be built over a crawl space, basement or slab, depending on the site conditions. And the total installed cost cost, with solar, for these approximately 1000 square foot units is running around $150,000.
These houses, while super-efficient, are not Passive Houses. Their air infiltration rate is close to Passive House level, but they do not have the standard Passive House energy recovery ventilation system, and they allow a few thermal bridges that would not pass Passive House muster. What VERMOD and VEIC found was that the sweet spot cost-wise in their situation was to take the house to nearly the Passive House level, and then add PV solar to take it to Net Zero. The typical solar array for one of these homes is a 6K system.
Instead of the heat recovery ventilator (or energy recovery ventilator) you would find in a Passive House, they use something called a CERV, which monitors CO2, humidity and VOC levels, and automatically switches on when those levels are activated. At the same time it does double duty as a small heat pump, distributing air throughout the house with a small duct system and running all incoming and exhaust air through its built-in heat pump component. This takes care of all the heating and cooling needs for the shoulder seasons. A little wall-mounted Mitsubishi mini-split provides back-up heating and summer cooling, with the CERV distributing that air equally throughout the house.
Hot water is handled by a 50 gallon heat pump water heater. This proves considerably more economical than using solar hot water, and also saves room on the roof for more PV panels. The cool exhaust from the heat pump is collected by the CERV in the summer, which distributes it throughout the house.
Construction is of double 2×4 wall construction (R-43) and trussed roofs with 12” raised heels to achieve an R-60 roof insulation value. Insulation is dense-packed fiberglass. This was chosen for its lower weight (important when shipping houses) and its slightly higher R value per inch. The floors are framed with 2×10 dimensional lumber with densepack fiberglass for an insulation value of R-40.
The Earthwise “Orion” windows, with insulated sash and frames, are from PVC Industries and manufactured in New York, not Europe or Canada. They have a U-value of .20. Earthwise’s upgraded “Revolution” series, with higher U-values, has been used in PHIUS certified Passive Houses.
Air sealing is accomplished using taped ZIPWALL sheathing on all exterior surfaces, including under floor framing and atop roof framing. In addition they are using an airtight drywall system: 5/8″ drywall glued to all framing, and all electrical boxes and penetrations fully sealed. Their most recent houses are achieving an air infiltration rate of .6ACH at 50 Pascales — Passive House level.
This is exciting work and we will continue to look for partners in bringing this kind of affordability to the Mid-Atlantic.