Building in Japan
Cutting edge energy-efficient designs are hard to find — and poorly insulated walls are the norm
Energy efficient houses are becoming more common in the U.S., even if progress sometimes seems halting. What about building practices in other parts of the world? Are builders elsewhere more progressive about using new materials and techniques, or sticking to the old ways?
We get one take on this question from Eric Matsuzawa of Connecticut, who's getting ready to build a house in a Climate Zone 4A region of Japan. Conditions would be similar to those of Virginia, not especially harsh. But what Matsuzawa is learning about local building practices is giving him pause for thought.
“Here is an overview of what I have learned of walls in Japan,” Matsuzawa writes in a Q&A post at GreenBuildingAdvisor. “The standard Japanese 2x4 wall from outside to inside consists of panels of artificial siding, a 1/2-in. vented rain screen, house wrap, 1/3-in. plywood sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. , a 17-in. [on-center] 2x4 stud bay insulated with 2-in. fiberglass batts, polyethylene vapor barrier sheet, and 1/2-in. sheet rock. Windows are aluminum frame and single pane.”
Although Matsuzawa originally intended to follow local building customs, he later learned that buildings are expected to last only 35 years. Further, he knows first-hand they are cold in winter and hot in summer.
“I would rather build one house and build it right so my family can live in comfort without exorbitant energy costs,” he says. “It seems to me that local building practices have too little insulation and I am worried about the interior vapor barrier with air conditioning on during the hot and humid summers.
“I have raised these concerns with local builders but they have tried to assure me that their methods are correct,” he adds. “Are my concerns well-founded? Would it be advisable to abandon local practices for a more efficient building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.?”
That’s the topic for this Q&A Spotlight.
Buildings reminiscent of the 1950s
As described by Matsuzawa, the house would have a whole-wall R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of 6, says Dana Dorsett, and to GBAGreenBuildingAdvisor.com senior editor Martin Holladay it’s a throwback to mid-20th century construction practices here.
“The house you describe is similar to homes that were being built in the U.S. in the late 1950s and early 1960s,” Holladay writes. “It's hard to buck the trend here in the U.S., where we have more than our share of builders whose methods are stuck in the past. I don’t know if you speak Japanese, but it can be even harder to buck the trend if you are an American in a foreign country where respect for one’s elders is honored.”
Mike Eliason thinks the 35-year life span of Japanese housing may be a function of making room for taller and/or denser housing, not necessarily their durability.
“Historically, Japanese walls had no insulation - so I guess 2-in. fiberglass batts is somewhat of an improvement,” Eliason says. “There is a small PassivhausA 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. community in Japan, so there are progressive builders and there is interest - and from what I understand it's grown fairly well since Fukushima Daiichi [the earthquake induced nuclear power plant failure in 2011].”
Eliason also offers a link to a description of an experimental house that suggests truly efficient building is a ways off.
“When one of the top architects puts together a cold-weather experimental house like this one (with no sub-floor insulation and a few inches in the wall/roof) one gets the feeling a fundamental paradigm shift on wall performance ain’t happening.”
Building performance isn’t helped by a resistance to advanced framingHouse-framing techniques in which lumber use is optimized, saving material and improving the energy performance of the building envelope. practices, Matsuzawa adds.
“I talked to them about advanced framing but they were sure that a house using it would immediately topple over in an earthquake,” he says. “We are in one of the most earthquake-safe areas of Japan, so I’m not so sure.”
Stephen Carlton also has been unimpressed with the buildings he’s seen there:
“I was in Japan in December and visited a site with over a dozen model homes by Daiwa,” he writes. “I was very surprised when I saw a wall section. There were no thermal breaks in the walls or windows, windows were all metal frames, insulation was pretty loose fill and would settle and I saw no real evidence of good air sealing.
“The rain-screen and roofing details were good, as one would expect in rainy Japan. They would not let me take a picture. To me the structures didn't seem to be energy efficient but the homes were heated by mini-splits.”
On the plus side, the per-square-foot cost of the houses wasn’t high by U.S. standards and interior finishing was “very nice.”
Exploring other options
There are other options, Hein Bloed says, referring Matsuzawa to Sekisui Chemical Co., which he says builds to the EnergyPlus standard.
“There are many more in Japan, but this one has the longest record,” Bloed says. “You can go to the pre-fab factory and watch your own house being build, taking friends and a camera with you. High quality, but probably not as cheap as the cardboard house you have described above.”
Matsuzawa, however, has heard of Sekisui and in fact lives in one of the company’s newer apartments, which he describes as a “pup tend as far as thermal comfort” goes.
“They might make houses to the energy plus standard but my guess is they are leaky structures in a mild climate with loads of PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. panels,” he says.
Another option might be structural insulated panels, says Gordon Taylor, particularly those made by Precision Panel. Taylor says they have been shipping to Japan since 1996.
He also directs Matsuzawa to a blog about a SIPs house in Japan.
“Evidently there are people there who have built and continue to build with SIPs,” Taylor says. “They're expensive here, and I'm sure they're expensive there, but you'd get an energy-efficient earthquake-proof house, for sure.”
Our expert’s opinion
Peter Yost, GBA's technical director, added these thoughts:
First, the context: Why would typical Japanese new homes be so lacking in energy efficiency? My guess is the long-standing Japanese tradition of heating objects, not rooms, and achieving thermal comfort more with clothing than thermal performance. An example of the former is the kotatsu and for a great read on overall thermal comfort and energy efficiency, see “Thermal Comfort in the Traditional Japanese House". The traditional Japanese approach to cold winters and hot-humid summers can be very efficient, albeit with a very different approach to thermal comfort.
Second, the issue of the polyethylene vapor barrier on the interior during active cooling: if the homes are as leaky as they seem to be, the poly is almost certainly doing more harm than good, although as described with the 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. and the walls being vapor-open to the exterior of the wall assembly, it may not be wreaking the havoc it would otherwise.
Third, the trouble with “more wood is good for earthquakes”: shear resistance and the overall stability of wood-framed walls to “shaking” is just as much, if not more, related to the type, number, and setting depth of fasteners as it is to the amount of framing.
Overall, it certainly seems that traditions and conventions have kept new homes in Japan from moving more than just tepidly and superficially into modern high-performance residential construction. But if your customers have abandoned heating objects and dressing for thermal comfort, Climate Zone 4a is no different in Hiroshima than Hampton.
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