Copyright 2011 by GreenBuildingAdvisor.com
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The goal of the Passivhaus standard is energy efficiency and air-tightness on the cheap, not a green label
Jason Kibbe is in the enviable position of planning the construction of a new house that will be financed entirely by the sale of his current home, leaving him in new digs without a mortgage.
Kibbe plans to swap his 4-bedroom, 2 1/2-bath house in south-central Pennsylvania for a 3-bedroom, 2-bath house of between 1,500 and 1,700 sq. ft, and he’s upfront about his motives:
“I confess my main motive for building is a selfish one,” he writes in a in a Q&A post at GreenBuildingAdvisor. “I’m not looking to spend a ton of cash just to be green, though I certainly don’t mind making some efforts to go in that direction. I primarily want to build an inexpensive house (because I’m cheap) that will have low energy requirements (also because I’m cheap & am concerned about rising energy costs).”
That’s clear enough. But is Kibbe’s best bet a particular kind of high-performance house, one built to the Passivhaus standard, or a more universal design relying on general passive solar principles?
Houses built to the Passivhaus standard must meet very stringent requirements for air infiltration and energy use. As such, they occupy a special corner of the high-performance building world, not only in energy efficiency but often in the cost of construction as well. Passive solar houses can be highly efficient, but the term in itself is vague.
When Kibbe wrote, “I wish there was a repository of building plans and suggested materials for use in a passive house,” it was unclear whether he had a Passivhaus or a passive solar house in mind. “I’ve been gleaning information from this site and others, but still struggle with what are the ‘best’ heating (radiant floor, heat pump, etc.), HRV, (brand, specs. to look for), window (brand, rating), water heater (electric, propane, tankless), etc. options for me.”
A punch list for energy efficiency
Kibbe’s search for fundamental answers about energy-efficient design isn’t unusual. As building science gets more sophisticated, it also gets more complicated. It’s easy to get lost in the details.
Building to the Passivhaus standard can be especially complicated, as GBA senior editor Martin Holladay suggests. “If you want to build a house that meets the Passivhaus standard,” he writes, “you will almost undoubtedly need to hire a Passivhaus consultant. Your house will cost significantly more than a house that does not meet the Passivhaus standard. The Passivhaus standard sets a very high bar, and such homes are not cheap, regardless of what some people claim.”
Given those realities, Holladay adds, maybe a more down-to-earth superinsulated house is all Kibbe really needs. And to accomplish this, he offers an abbreviated list of requirements:
- A simple rectangular shape (no bump-outs), with the long axis oriented east-west, two stories.
- About half of the windows oriented to the south, with few windows on the north side.
- Basement walls rated at R-20, above-grade walls at R-40 and a ceiling of R-60.
- Exterior walls framed with two rows of 2x4s for a total thickness of 12 in., insulated with cellulose.
- An unconditioned attic insulated with cellulose.
- Canadian triple-glazed casement and fixed windows with fiberglass frames.
- A heat-recovery ventilator with dedicated ducts.
- A Mitsubishi ductless mini-split for heat.
In response to a follow-up question, Holladay added a few further recommendations: “A superinsulated house in Pennsylvania should have insulation under the basement slab — at least R-10, and more if there is hydronic tubing in the slab. And it goes without saying that the designer and builder should have a plan to achieve airtightness goals as well.”
“Maybe Passivhaus is too extreme”
The Passivhaus approach isn’t universally popular with advocates of high-performance houses, and even some early advocates have dialed back their enthusiasm.
“I like Martin’s post,” writes John Brooks. “I admit that I once thought Passivhaus might be ‘the solution’ for North America. I was angry at Martin, John Straube and Robert Riversong for suggesting that some aspects of the Passivhaus system were ‘murky’ and or not-so-logical.
“I am always looking at U.S. Passivhaus examples and so far have not seen one that I would call practical. (Please post a link if you have seen one.) Perhaps Passivhaus is too extreme.”
And finding a middle ground between the strict requirements of Passivhaus construction and the more general objectives of passive solar construction is the point Tim Shepp seems to be making: “You can build a passive [solar] house from almost any standard building materials … nothing fancy needed,” Shepp says. “The biggest concern is can you orient the house due south or at least have lots of glazing on the south side … A passive [solar] house is not much more expensive to build than a normal house,” he says. “It’s how you build it that is important. Get a good book on how to build a passive house (not Passivhaus) and search the Web. Lots of info out there.”
Other suggestions for good design
Holladay isn’t alone in making suggestions for Kibbe’s new house.
J Chesnut suggests hiring a designer with expertise in passive solar design, if not a Passivhaus specialist. “A Passivhaus designer like any other professional is responsible for helping you meet your budget,” he says. “If meeting the budget means falling short of the voluntary Passivhaus standard, that is possible. The benefit you still receive from hiring PH designer is energy modeling that will help make intelligent decisions … A good PH designer will also pay the appropriate attention to airtightness and avoiding thermal bridging that could undermine the performance of the insulation.”
Brooks recommends a one-story house with no basement or crawlspace. And while you’re at it, he adds, skip the vaulted ceilings.
“If you can’t live without storage space for cars and ‘stuff,’ build a shed,” Brooks says “The advantage to a one story (with flat ceiling) is that you will have less exterior wall surface area and more ‘attic floor’ area. Attic floor area is where you will get more bang for your dollar as compared to exterior wall area.”
Daniel Ernst writes that if Kibbe follows Holladay’s recommendations, most of the energy he’ll need for the house will go to domestic hot water, appliances, and plug loads. In that case, Ernst says, add a condensing gas water heater (or a hybrid system incorporating an instant water heater and small buffer tank), Energy Star appliances, and switched receptacles to control phantom loads drawn by televisions, computers, and the like.
Kevin Dickson’s list would include a frost-protected slab, 100% electric appliances (no gas use in the house), no sliding doors or windows, a solar hot water system, triple-pane fiberglass windows, and a minisplit heat pump.
“DO hire a HERS rater ($1,500 maximum),” he adds. “DON’T waste money on LEED or PH certification.”
Don’t forget the budget
The original post made it clear that keeping costs down was a major goal, Joseph Garten points out. “So the first advice I would give him is to identify a realistic budget,” he says. “Once a budget is identified for the project then a discussion about the different strategies and approaches for ‘green’ can be more on target.”
Among the variables are land and construction loan costs, required site work, and the availability of public water and sewer. “All these things add to the cost of the project before the house is even considered and might dictate choices for ‘green’ details and the overall approach to the project,” he says.
Spending priorities are always an issue with homeowners and builders of ordinary means. “Talking with friends who have recently bought ‘production’ style homes, it seems that one reason energy-efficient homes are considered too expensive is the assumption that envelope improvements have to be paid for in addition to interior finishing costs,” writes Lucas Durand. “Given a choice between spending money on envelope improvements or maxing out on expensive trimmings, it seems that the average consumer will usually choose the latter. I wonder how many production builders offer envelope packages in the same way that they offer finishing packages?”
Our expert’s opinion
We asked GBA technical director Peter Yost for his take. Here’s what he had to say:
“I am right with Martin on this one—his list is a very good one: simple design saves money and energy. And if the air tightness of the building reflects the R-values (20-40-60 for foundation, walls, attic—and high performance windows), then the space conditioning loads can be handled with the ductless mini-split.
“Martin mentioned hydronic tubing in passing with respect to the basement slab; radiant floor distribution is expensive and any dollars spent on this type of system would be much better placed in other mechanicals or the envelope.
“With mechanicals and an envelope at this performance level, then going after the other loads, one by one, as budget allows makes sense: domestic hot water, appliances, lighting, then plug load.
“A design and siting as Martin suggests may be all the design guidance Jason Kibbe needs, but it would be a shame to get the specs and construction right and have even one element of poor design wash away some portion of high performance. It is almost as if stock plans at this level of performance are a contradiction in terms; you need to tune even simple home designs by climate, site, and client preferences.”