Passive House Sets High Bar for Energy Efficiency
By: Brent Runyon
A new home under construction in East Falmouth is being built to an exacting new building standard, designed to be super-tight with virtually no air leakage, which may make it one of the most energy-efficient houses in the United States.
“Upon completion, this will be one of the top 10 energy-efficient houses in the country,” said architect Steven Baczek of Reading. “The house is virtually a hot air balloon.”
The standard of building called passive house is based on a European model that is becoming more popular in the United States. There are currently only 14 certified passive houses in the country.
An active passive approach
The idea is to build a home that is heated mostly with natural sunlight, super-insulated to maintain the heat, and ventilated with a mechanical system that transfers out the stale air and moves in fresh air, maintaining ideal temperatures and humidity levels within the house.
“If you talk to old-time builders, they’re going to say that you don’t want to build a house too tight, you want it to breathe,” Mr. Baczek said.
“I agree with that, but where I differ from them is when I say the house is going to breathe, I predict and control where it’s going to breathe from.”
Comparing the house to a human body, Mr. Baczek said where the air and water enter and exit the home are carefully designed for maximum efficiency.
The house is so tight that the only air leakage is from a maximum of five holes in the exterior, equaling the total area of a three-by-five inch index card, he said.
The home will be heated by large south-facing windows that warm the house during the day, and by a mechanical ventilation system that moves the air throughout the house using the bathroom fans.
A heat exchange unit functions as an air conditioner in the summer and a heater in the winter, transferring the energy from the hot or cool stale air to the fresh air.
From the exterior, the home looks just like any other construction site. A metal roof and photovoltaic solar panels are the only indications that the home is intended to be energy-efficient.
Inside, although there are no windows, doors, or mechanical components installed yet, the builders have already begun to insulate the house with a rigid foam insulation.
The Valle Group in East Falmouth is the contractor. Christian T. Valle toured the house on Wednesday morning as sunlight dappled across the roof and southern-facing facade.
When complete, the house will have R-100 insulation in the attic, R-60 in the walls, and R-70 in the floor, he said. The construction is actually a frame within a frame, with 17 inches for insulation between the exterior wall and the interior of the house. There will be three layers of insulation in the walls, a rigid foam layer, closed cell foam, and blown in fiberglass insulation, he said.
Construction began in August, and will be completed this spring, Mr. Valle said. The builders are currently awaiting a special order of triple-glazed windows from a Canadian company called Thermotech windows, which will allow sunlight and heat into the home, but minimal heat to escape.
The interior of the home is a simple two-story structure, with one central staircase, and an open floor plan on the first floor and bedrooms upstairs.
It can be about 20 to 25 percent more expensive to build a passive house, Mr. Baczek said, but the design is not without benefits.
When complete, Mr. Baczek said, the home will use 80 percent less energy than a similarly sized house. Add to that the photovoltaic solar panels and solar-heated water, and the home is expected to be a zero net energy home.
The three-bedroom, two-and-a-half bath-house will have 1,900 square feet of finished space with no basement. The house is built on a slab with a crawl space filled with insulation.
A similarly outfitted house might cost $300 per square foot to build, he said, while the passive house costs an estimated $350 per square foot.
A tight envelope
Michael B. Duclos, a consultant in passive houses from Stow, created a computer model of the house to test the heat loss and mechanical ventilation system before construction.
During construction, the house is tested for air-tightness by using a blower door test. On Tuesday, the blower door test showed only a few leaking spots.
“We’re building and testing it as we go,” said Mr. Duclos. To reach the passive house standard, the builders and engineer must show that the house met the standard at each construction phase.
The building standard has gained popularity in Europe over the past 10 years, according to Paul Eldrenkamp, a passive house consultant in Boston. In Austria, he said, 25 percent of all new construction is being built to the passive house standard.
Mr. Eldrenkamp, founder of the Boston-based Byggmeister, which is the Scandinavian word for master builder, said he took the first course ever offered in passive house consulting in the United States in 2008.
There are only 14 completed passive houses currently in the country, with another 50 to 60 homes in the planning or construction phase, he said.
The key to a passive house is the heat ventilation system, which passes the heat from the outgoing stale air to the incoming fresh air.
“In a well-designed system, it can recover 75 percent of the heat from the exhaust air,” Mr. Eldrenkamp said.
Needless to say the house will not have a fireplace. There will also be no gas burning devices. Even the clothes dryer is a condensing dryer that has no vent to the outside to maintain the air envelope within the house, Mr. Baczek said.
Buildings are responsible for 48 percent of greenhouse gas emissions annually and 76 percent of all electricity generated by United States power plants goes to supply the building sector, according to data from the United States Energy Information Administration provided by the Passive House Institute of the United States.
Passive house certification carries no tax incentives or rebates, but the house will be a tier four, Energy Star home, which qualifies the owner for some rebates, Mr. Baczek said.
The home is on Upalong Road in Davisville on Bournes Pond and can be seen from the Menauhant Beach area.
The 5.7-acre parcel and existing cottage were purchased in 2009 by Daniel Kahn of Needham for $1.19 million in 2009, according to town records.
One drawback might be that the house relies so much on mechanical ventilation, that when the power goes out, the air will become stale. The solution is simple. “Just open a window,” Mr. Valle said.
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