Reaping the Energy Rewards of Passivhaus Design
A Canadian couple marks the end of their first year of energy monitoring in a house built to the Passivhaus standard with a heating bill of less than $100
Beth and Ralph Peters and their four children have just passed the one-year mark in their new home on Prince Edward Island, and can report that their energy-saving efforts have more than paid off. The total heating bill for the year, all 754 kilowatt-hours worth of it, was $99.23. That's pretty good for an area that sees about 8,000 heating degree days a year.
The family used a total of 10,029 kWh of electricity — about $1,872 worth — for all purposes during their first year of occupancy.
The Peters family is living in a house built to the Passivhaus standard. The house would have been the first Passivhaus building in the province if the owners had pursued certification. The $5,000 plus cost of certifying the house was more than their budget allowed, but they've been reaping the rewards nonetheless.
They turned the heat on for the first time this season in November, as Beth Peters explained in a blog called Long River House.
"Ugh, I did not want to make this post but, alas, we have had to turn the heat on," she wrote. "And by heat I mean our one 1500-watt heater."
Making plans for a new home
About ten years ago, the Peters first spotted the property on which they would eventually build. The parcel is in the town of Long River, the same community where they had been living and where they wanted to stay.
"It is a total of seven acres and is surrounded on three sides by trees, which should offer us good protection from the wind," she wrote. "It is also the last property on a paved road and is much quieter than the road we used to live on."
The Peters didn't immediately decide to go the Passivhaus route. They were interested in energy-efficiency, and when they began poking around that topic, trying to meet the Passivhaus standard became more appealing. They also recognized that they would need some serious design help, so they contacted Garth Hood of Thoughtful Dwellings, a certified Passivhaus consultant in neighboring New Brunswick.
"I think there might be a Passivhaus consultant on the island now," he said recently by phone, "but at the time I was the only game in town, so they went with me."
Hood designed the house and perforemed the energy modeling, a dual role he says he took out of necessity.
"I've yet to find a designer in New Brunswick that understands how to design an energy-efficient house," he said. "I started my work just doing the energy modeling part, but it was such a hassle for me to redesign houses that I just started designing them. You don't come to me if you want a California roof. I just don't do that, and those clients leave very quickly. I tend to design with Passivhaus first and foremost in mind, so they tend to be boxy houses. If they want interest we tend to put on porches and things."
By February 2014, Hood and the Peters were close to completing the plans. "It has been really tough poring over plans," Beth wrote. "How do we cram everything we want into our box?"
But cram they did, and in the end the family managed to get what they wanted in 1,950 square feet, a house that might seem tight for a family of six.
An early encounter with energy modeling
By April, the project was far enough along to dive into the energy modeling, and the numbers stunned the Peters.
Exterior walls are 21 inches thick and insulated with dense-packed cellulose.
The Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. Planning Package that Hood was using to design the house gave an energy credit of 100 watts for each person living in the house, Beth wrote, adding up to an extra 600 watts of free energy in winter.
"So, with all this taken into consideration, our estimated additional required energy is 187 watts," she wrote, "187 watts! That’s not much! As a comparison, the numbers are calculated as well for a house build to code; that came in at a whopping 8,628 watts! So what does this really equate to? Well, if we were to run a 187 watt heater for 24 hours a day, 7 days a week, for 150 days a year, that would work out to be $81.46! On the contrary, if I did the same calculation for a code built house my bill would come in at $3,758.35. Wow!"
Another way of looking at it, she added, was that in the old house they were renting at the time, the bill for a single delivery of oil would be enough to heat their new home for 11 years.
They were hooked.
"The best part of it all (besides saving money) is that we are conserving energy and still living comfortably," the blog says. "Saving money and helping to save the planet: sounds like a match made in heaven to me."
Builders from Prince Edward Island, Terry and Natalie Perry of Trout River Homes, got some pointers on Passivhaus construction from Tim Naugler in New Brunswick, with whom Hood had worked with before. To save money, Hood didn't draw a comprehensive set of Passivhaus construction details.
Builders broke ground on July 8, 2014, beginning with site preparation for the 6-inch thick layer of Type II expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.) insulation that would insulate the slab. Slab edges are insulated with 12 inches of EPS.
- Exterior walls: The 21-inch-thick walls are comprised of a structural 2x6 assembly and an outer 2x4 joined with webs of OSB. Between the 2x4 and 2x6 bottom plates is a 6-inch space, and on the inside of the 2x6 wall there is a non-structural 2x4 service wall. All cavities are filled with dense-packed cellulose to R-60. Wood siding was installed over a vented rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. gap.
- Roof: Raised-heel trusses insulated with loose-fill insulation to R-74.
- Ventilation: A Zehnder ComfoAir 350 heat-recovery ventilator provides fresh air for the house. What the blog describes as a "poor man's geothermal" system, a 500-foot long tube filled with glycol and buried 6 feet in the ground, tempers incoming air in the HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. . (For more information on this type of glycol loop, see Using a Glycol Ground Loop to Condition Ventilation Air.)
- Domestic hot water: Tank-style electric resistance water heater.
- Windows: Klearwall triple-glazed tilt-and-turn vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). windows manufactured in Ireland. Windows are set at about the midpoint of the wall.
- Air leakage: In exterior walls, the air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. is a layer of taped OSB just to the outside of the 2x4 service wall; in the roof, a membrane made by Mento is the air barrier. A blower door test measured air leakage at 0.21 air changes per hour at a pressure difference of 50 pascals.
- Energy use: Total energy use during the first year of occupancy was 10,029 kWh. Interestingly, the family used 6 times as much energy for heating domestic hot water as they did for space heating. Energy monitoring showed that the Peters used 4,741 kWh for miscellaneous electrical loads (including lighting), 4,534 kWh for the water heater, and 754 kWh for the electric space heating element. A spreadsheet showing monthly energy use is posted at the blog.
There currently are no renewable energy systems in the house, but the couple plans to add photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. panels once they'd been in the house long enough to size the array correctly. The couple didn't divulge construction costs.
The family moved into their new home in February, 2015.
No certification is planned
Hood thinks that the house is close to meeting the Passivhaus standard, but the cost of going through the certification process was enough to deter the Peters from trying.
"They were talking about certification until we got to all the costs that would be involved," Hood said, "and then the conversation dropped off." He estimated costs at a minimum of $5,000, and possibly as high as $7,500.
"I can't say for sure they would meet the Passivhaus standard," he said, "but they are very, very, very close."
Is it something the Peters might want to pursue in the future? "Probably not," Beth replied in an email. "It is an added cost (which is significant) that we would prefer to put into something like solar electric."
If the family had the project to do again, Beth said, they would turn the small covered deck on the west side of the house into an insulated mudroom outside the thermal envelope of the house and put the washer and dryer there.
"Most of the time, it's not an issue not having a dryer in the house [it's now located in a shed], but we do miss the convenience of it sometimes," she wrote. "Hopefully, it won't be too long and heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump. dryers will be readily available. Overall, we are extremely happy with the design and functionality of the house. It works perfectly for our family."
- All photos: Beth and Ralph Peters
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