The energy-savings principle behind a “passive house” design is as the name implies: the structure is built to economize. The mechanical systems – heating and cooling, among others – have to work much less, and can be smaller, because they have less to do.
How this works for multifamily structures in Rhode Island is going to play out over the next several years.
At least two passive houses – single-family houses – have been built in the Ocean State. But the commercial application of the design standards is just starting to move forward.
One of the first proposals was put forward by Providence-based Truth Box Architects, which has unveiled plans for a seven-unit, multifamily building, over three floors.
The project at 1492 Westminster St. would place the new construction over an existing parking lot. The site was purchased by the company in 2011, said Peter Gill Case, principal.
Working with a passive-house-certified consultant, Case is preparing a design that would include seven rental apartments, as well as a retail space on the ground floor. One of the apartments would be accessible to people with physical disabilities. Others would likely be one-bedroom units, he said.
The small scale is ideal to roll out the passive-house design standards. “We’ve been doing multifamily units that are larger – 30 units,” Case said. “We didn’t want to go all the way to a passive house, experimenting first, on a big one. This was a small lot we bought in 2011.”
The idea is to incorporate a passive-house design in a multifamily structure, leaving the tenants with comfortable, ultra-efficient surroundings.
The principles of a passive house, according to Passive House Institute U.S., include the following: employing continuous insulation, without any thermal bridging; building an airtight envelope, preventing air leakage; using high-performance, triple-paned windows and doors; employing a heat and moisture recovery system; and orienting the windows and structure to take advantage of solar.
It’s all about comfort, not a particular energy standard, according to Case. But in general, passive houses use about 20 percent of the energy of a code-compliant house, he said.
‘There are no cold surfaces, anywhere. Not even cool.’
PETER GILL CASE, Truth Box Architects principal
“When you go into a passive house, certain things you will notice,” he said. “There are no cold surfaces, anywhere. Not even cool. All of the surfaces are the same temperature. The air temperature has a difference of a couple of degrees, versus 10 to 15 degrees, whether you’re lying on the floor or [are] up at the ceiling, hanging a painting. There is very little variation of temperature.”
One of the ways that this “passive” state is achieved is through positioning of windows, to capture the heat of the sun, and then installing a mass of material that will absorb that heat and radiate it out over the night, when the sun goes down.
In a single-family house in South Kingstown, built to align with passive-house standards, that heat capture is achieved through large windows and a massive floor of polished granite, which has an insulation barrier to keep it from feeling cold to the touch, said Joe Haskett, a senior associate with Providence-based Union Studio Architecture & Community Design Inc., who is certified as a passive-house consultant.
When a house can be positioned on its lot to face the south, this is ideal. But even without that orientation, passive-house standards for efficiency can be met, he said.
In the case of the South Kingstown house, which he designed, and which was built by Steve DeMetrick, owner of DeMetrick Housewrights LLC, and a certified passive-house builder based in the town, the house uses solar panels to generate energy. It has for the last five months performed at net energy positive, meaning it produces more energy than it uses.
“The passive-house principle is you design it passively, to use such small energy load, and then you cover the gap with renewable energy,” Haskett said. “In this case, it’s solar panels on the roof.”
Haskett has designed two houses with passive-house principles in Rhode Island. In addition to the South Kingstown house, which is home to a family of six, he’s designed a house in Warren.
His clients are motivated primarily by the environmental benefit of having no impact on greenhouse emissions. And they’ve had to research it a bit, as well, Haskett said, because passive houses remain relatively unknown in Rhode Island.
He’s hoping that changes. His company is starting to work on a proposal for a 24-unit affordable-housing building that could be designed with the principles. The additional cost is not prohibitive, he said.
The South Kingstown custom house was designed and built for about $220-$250 per square foot.
“The approach is kind of anti-technology in the sense that we’re trying to build the house, robust-passively,” Haskett said. “[With] insulated walls, airtight construction, good, high-performing systems. The load is so low on a house like this that the systems become very small.”
