One of the presentations I attended at the Passive House conference in Portland, Maine, on September 22, 2014 was a session called “Passive House certifiers’ roundtable.” The first speaker on the panel, Tomas O’Leary, explained that he usually charges about $2,200 to certify a residential Passivhaus project. He warned the audience that certification is “quite an effort; don’t underestimate it.”
Tomas advised that anyone interested in certifying their Passivhaus should remember the following important steps:
- Prepare, collate, and submit the construction and mechanical details.
- Photograph all critical details.
- Make sure you get an HRV commissioning report.
- Remember that your blower-door test has to be performed twice: under both pressurization and depressurization conditions.
- Make sure that you enter the right climate data into PHPP; data from a nearby weather station might not be good enough.
- Enter the correct U-factors for all of the window components — Uframe, Uedge, Uglass — because each component has to be modeled.
- The R-value per inch of all relevant materials has to be documented. Listing the R-values is insufficient; each R-value requires a document that justifies the listed value.
- Document a 360 degree panorama of the shading situation at the building site.
Is each one of these details really essential for determining whether a house can be certified as a Passivhaus? Absolutely.
If you are in any doubt about this issue, remember that one of the cited causes of the famous divorce between the Passivhaus Institut in Germany and Passive House Institute U.S. was a dispute over the details of the certification documents for a house in Canada. The dispute centered on two points: whether the efficiency calculations for a Canadian HRV met the strict efficiency calculation requirements specified by the German institute; and whether an evergreen tree was tall enough to invalidate the shading calculations entered into PHPP.
Getting stuck in the weeds
I admire energy nerds who use THERM modeling for all kinds of complicated building assemblies. I really do. We can learn a lot from THERM modeling calculations.
I’m grateful that someone has made the calculations to determine that in-betweenie windows perform slightly better than outie windows. Now we know.
I’m also grateful that Stephen Thwaites and Bronwyn Barry are available to explain the subtle differences between the way window U-factors are calculated in Europe and the way they are calculated in North America.
But when I hear lengthy discussions on these issues, I sometimes think we’ve fallen down the rabbit hole. If you are a builder or a designer rather than a building scientist, it may be time to clear the air. It’s sometimes important to balance the recommendations of Passivhaus engineers with some common sense.
Since it’s getting hard to breathe down here, I’ve decided to pop my head out of the rabbit hole and write my Pretty Good House Manifesto. It’s time to identify which features really matter.
1. We need to be humble
I’ve heard Passivhaus builders justify expensive construction details by explaining, “Europeans build houses to last 200 years.”
Well, yes. That’s kind of, sort of, true. But we should remember that 200 years ago, buildings didn’t have central heating, insulation, plumbing, or electrical wiring — so you wouldn’t really want to live in one. At best, a 200-year-old building is kind of like a shipping container. It’s a rigid shell inside of which you can build a modern house.
It’s hard to know what kinds of homes will be desirable in 2214. In 200 years, maybe everyone will be living in electric cars. Or boats. It’s really hard to know whether a 200-year-old Passivhaus building will be considered desirable or a quaint relic in 2214.
My first wife’s mother was raised in a solidly built 200-year-old farmhouse near Dingle, Ireland. There were 12 children in the family growing up together in the two-room stone house. The house never had running water or electricity, and it is now being used as a sheep barn — about the only purpose it is fit for.
Thousands of solidly built homes in Detroit have been abandoned, and I suspect that in the coming decades, tens of thousands of homes in Arizona will also be abandoned.
In the U.S., we demolish buildings at a surprisingly fast clip. Nice homes often end up too close to a busy road, or in a neighborhood where no one wants to live.
How many of today’s $500,000 Passivhaus homes, each of which was “built for 200 years,” will end up getting an addition? Perhaps a second story? Maybe a remodeled kitchen that needs a bump-out? The fact is, we don’t know.
One thing’s for sure: building a house that is designed to last 200 years is guaranteed to be expensive.
All of these arguments support a building philosophy that Stewart Brand called the “low-road” approach. Sometimes, a small, inexpensive house makes sense.
2. Airtightness matters
The Passivhaus standard may have gone off the rails with its space heating energy budget (15 kwh/m2•year), but they got the airtightness target (0.6 ach50) just about right.
If you want to build a good house, pay attention to airtightness during construction. Once your windows and doors have been installed, perform a blower-door test. Reducing air leaks is the most cost-effective way there is to lower your energy bills.
3. There is nothing wrong with rules of thumb
Study buildings in your climate zone that are attractive, simple, and energy-efficient. Pay attention to their specifications. If possible, talk to the residents and find out whether the buildings are working well.
If you do this, you will develop a gut instinct for what works in your climate zone. Eventually, these instincts can be codified into rules of thumb.
A well-known rule of thumb for cold-climate builders in North America is the 5-10-20-40-60 rule developed by the Building Science Corporation: windows should have a minimum R-value of 5 (equal to a U-factor of 0.20); basement slabs should be insulated to R-10; basement walls should be insulated to R-20; above-grade wall should be insulated to R-40; and attics or roof should be insulated to R-60.
Although some Passivhaus designers ridicule the rule-of-thumb approach as unsophisticated, it works just fine. It gives designers a guideline for good work, but it isn’t set in stone. One of the implied corollaries of this type of rule is that it is somewhat flexible. After all, R-35 walls also work just fine. So does an R-55 attic.
4. We need to include PV
If your building site allows you to build a house with an unshaded south-facing roof, you should include a PV array — especially if you live in an area served by a utility that offers net-metering contracts.
Whether or not your house includes a PV array, designers need to learn how to compare the kilowatt-hours saved by any proposed energy improvement with the number of kilowatt-hours that could be generated by a PV array of the same cost. The calculation really isn’t that difficult; I explained how to do it back in my 2011 article, Net-Zero-Energy versus Passivhaus.
Among the designers who use this method are Marc Rosenbaum, an energy engineer at South Mountain Company, and David Posluszny, a Massachusetts owner/builder.
Here’s an example of how the method works: Posluszny knew that he could save a few kWh each year by upgrading from double-glazed windows to triple-glazed windows. Was the upgrade worth it? It turned out that a few extra PV modules on his roof would generate more energy than the window upgrade would save — for the same investment. So he chose the double-glazed windows.
Of course, performing this type of calculation doesn’t obligate the designer to always choose the option that provides the lowest-cost reduction in a home’s annual energy budget. In the case of Posluszny’s calculation, a designer could justifiably decide to specify triple-glazed windows, based (for example) on improved occupant comfort, even if that decision increased the construction budget. But it’s important to make these decisions consciously, with an understanding of the cost and benefits of envelope improvements compared to the cost and benefits of a PV system.
5. We need to size and orient our windows with an eye to comfort and delight, not passive solar gains
Forget about specifying oversized windows for your south elevation. The bigger you make your windows, the more money you are wasting.
In other words, stop thinking that south-facing windows are a good way to heat your house.
Passive solar design principles from the 1970s need to be re-examined in light of an astute analysis made by Gary Proskiw. Proskiw wrote, “The reason the two window upgrades [in his study] fared so poorly, from an economic perspective, is that the space heating load in a NZE [net zero energy] house is very small compared to any other type of house. By adding window area or upgrading window performance, the space heating load is reduced but it is already so small that there is little opportunity for further savings.”
Proskiw concluded that “window area should be limited to that necessary to meet the functional and aesthetic needs of the building.” Isn’t that liberating? Just put in a window that looks good and suits your needs — no bigger. It’s pretty simple.
There is a side benefit to this approach: your house is less likely to overheat during the summer.
Of course, it still makes sense to locate your main rooms on the south side of the house (since people like natural light) and to locate your mudroom, pantry, hallway, and mechanical room on the north side of your house.
6. All-electric homes make sense
As we make the transition to renewable energy, it makes sense to avoid appliances that burn carbon-based fuels like natural gas and propane. All-electric homes make sense — especially if you are able to include a PV array on your roof.
7. Pay attention to domestic hot water and miscellaneous electrical loads
If you have designed a tight, well-insulated home that isn’t too big, you will probably find that you are using more energy for domestic hot water than for space heating. To reduce this slice of the energy pie, consider installing a heat-pump water heater and a drainwater heat recovery device. (For more information on this topic, see It’s Not About Space Heating.)
Limit the urge to buy new electrical gadgets for your home. Every time you specify an appliance, look for an Energy Star label.
Needless to say, it’s important to keep incandescent light bulbs out of your house. LED technology has now advanced to the point that you can find an LED lamp for every application.
8. Think twice before purchasing expensive building components
Every generation of designers lusts after a must-have building component. Back when I was building my first house in 1974, it was a Jøtul wood stove. Sure, it was expensive — but it was Scandinavian, and it got a good review in the Whole Earth Catalog.
These days, the must-have building component might be a triple-glazed Zola window from Europe, or a Zehnder HRV with a glycol ground loop.
Here’s the thing: if you find yourself saying, “I know it’s really expensive, but it’s supposed to be the best one on the market,” stop and ask yourself whether you really need it. In another eight years, it’s just going to be an old Jøtul stove, and there will be something else new and shiny that everyone is talking about.
A Pretty Good House can usually be put together with pretty good components.
9. We need to monitor our energy use
For most homeowners, “monitoring energy use” just means keeping track of our electricity, gas, and oil bills. We need to pay attention. Are we using more than our neighbors? Are our bills going up or down?
The nerdier members of our tribe will go a step further, and will install electrical sub-meters, HOBO sensors, and eMonitors. That’s fine. We all learn a lot from paying attention to actual energy use. Energy monitoring provides data, and data matter much more than projections developed by computer modeling programs.
This philosophy — monitor energy use and pay attention to what’s happening — is far better than the usual approach (namely, “I got a plaque to put on my house and now I’m done”).
10. Occupant behavior affects energy bills
While low energy bills are obviously desirable, we need to remember that the construction details of the house don’t tell the whole story. The other side of the coin is occupant behavior.
If you follow your grandmother’s advice — Don’t leave the water running! Turn out the lights when you leave the room! — you’ll save energy. If you build yourself a new 3,000-square-foot Passivhaus and install a big plasma TV and a second refrigerator, on the other hand, your energy bills are going to be higher than mine. For more information on this topic, see Occupant Behavior Makes a Difference.
Some energy-obsessed designers spend weeks trying to track down a European window that will nudge their design from 16 kWh/m2•year to 15 kWh/m2•year — a difference that might save $12 a year in a 2,000 square foot house. When the house is completed, however, it turns out that the teenagers in the family like to take 30-minute showers in the winter, and dry their hair with hair dryers during the summer. At that point, the $50,000 that you invested in European windows starts to look like a bad investment.
If you want to tread lightly on the planet, plan to live in a small house or apartment. Don’t waste energy.
If you follow these simple rules, your lifestyle is probably already greener than that of your wealthy neighbor who just built a brand-new Passivhaus — especially if you bicycle to work.
Martin Holladay’s previous blog: “A New Ground-Mounted Solar Array.”