“Passive housing” doesn’t refer to a home with a nonchalant nature. This European design concept is catching on across the U.S. and has been recognized by the Department of Energy’s Challenge Home program as the best path toward homes that produce as much – or more – energy as they consume. The basic tenet of the approach: build a home smarter from the ground up, and you won’t need to consume – or produce – as much energy.Laying the Passive House foundation. | Photo courtesy of Rob Harrison.
“Green without gizmos.”
That’s how an article in Fine Homebuilding magazine aptly referred to the passive housing approach. Based on the stringent “passivhaus” German building standard, it focuses on using specific construction methods and materials to achieve 60% to 70% in energy savings and 90% savings in space heating – and that’s without the use of technologies like photovoltaic panels, geothermal heating and cooling systems or solar water heaters.
Instead, passive housing relies on systems that conserve energy – by maximizing gains and minimizing losses, according to the Passive House Institute U.S. (PHIUS).
Features like superinsulation, an air-tight building envelope, and high-performance windows and doors, mean that conditioned air can’t leak out – nor can outside air sneak in. An energy recovery ventilator (ERV) is then used to provide continuous fresh air while reducing energy needs. The system captures the energy from outgoing “stale” air and transfers it to incoming fresh air.Although it may look complicated, the principles of passive housing are relatively simple. | Photo credit: Passivhaus Institut derivative work: Michka B, via Wikimedia Commons.
Depending on the climate, many passive homes don’t even need traditional heating and cooling systems – relying on just the ERV, passive solar energy techniques (such as orienting a home to maximize sunlight) and internal heat sources including appliances and even occupants. According to PHIUS, “knowing about the thermal storage capacity of certain materials and their “passive” effects on indoor temperature, the architect/designer can plan for enough thermal storage mass in a house by specifying tile floors, finished concrete slabs, concrete or granite countertops, stone fireplace surrounds, adobe walls or earthen plaster.”
According to PHIUS, while many new homes address energy leaks in the home’s envelope, most are not properly ventilated, which allows moisture to build up – encouraging mold growth – and traps indoor allergens. The ERV, by comparison, provides a continuous supply of filtered fresh air, providing “a huge upgrade in indoor air quality and consistent comfort, especially for people sensitive to material off-gassing, allergies and other airborne irritants,” according to the Passive House Alliance.Indoor staircase photo courtesy of Mike.
The home’s tight envelope and constant circulation also yields a consistent temperature and draft-free environment, according to the Passive House Alliance. And those super-thick walls? They block outdoor noise as effectively as unconditioned air.
Without the need for expensive systems or even a furnace, proponents say passive housing offers an affordable, everyman’s route to “net zero performance” – living in a home that generates as much, or more, energy as it consumes over a year. A builder in Maine recently estimated the annual cooling costs of a new 1,500-square-foot home would total $250 to $300, compared to $1,000 or more in a home built to traditional standards.
The UK’s first Passivhaus photo courtesy of NBT Natural Building Technologies.
But the upfront cost is always a factor in home construction, and while owners will reap future energy savings, passive homes typically “require an additional upfront investment of approximately 10% of the construction budget, as compared to regular energy code-compliant 2×4 construction,” according to PHIUS. But increasing material costs in the U.S. could make the homes up to 20% more costly to build, according to a July article in The Daily Mail.
Gaining ground, facing challenges.
The number of passive homes in the U.S. has increased tenfold over the past two years – now totaling about 120, according to PHIUS. And that doesn’t include projects that are built with passive housing principles but aren’t pursuing PHIUS certification, as a Boston Globe reporter documented last month.
Yet challenges remain in the widespread adoption. There are lingering misconceptions that the “tightness” of a passive house jeopardizes indoor air quality or prevents the owner from opening the windows – neither is true, according to PHIUS.
And as the concept has spread far beyond Central Europe – and its cool, moderate weather, experts have realized one set of passive housing standards doesn’t suit all climates. The Passive House Institute is currently creating climate-specific guidelines, which will better address the extreme climates seen in the southernmost and northernmost U.S. states. With the possibility of passive housing gaining ground across the country, are you ready for über-efficient homes in your neighborhood?Cover photo credit: Harald Brekke (Stein Stoknes) via Wikimedia Commons.