We use storage heaters in the winter, and they do a good job of keeping our two-story house uniformly warm, but the technology was partially based on the idea of off-peak electricity, meaning the ceramic bricks inside the storage units are heated in the middle of the night when electricity is cheaper and we’re asleep. Unfortunately, when our utility raised rates more than a year ago it also did away with off-peak discounts and last winter our electricity bills almost doubled. This year it’s been a bit better owing to government intervention, but anyone who lives in Japan, especially if they grew up in Europe or North America, understands how poorly Japanese homes retain heat. For one thing, central heating is not common in Japan, which means each room needs to have its own heat source, be it electric, gas, or kerosene. But the main reason for Japan’s cold houses is poor insulation due to lack of proper design standards that are mandatory in other countries. Even China and South Korea have strict insulation standards they adopted to address energy conservation needs and lower carbon emission targets.
Japan does have standards for insulation, and they were last upgraded in 1999. At the time, these standards were called “next generation energy conservation protocols,” but, in truth, they aren’t even mandatory, thus making Japan unique in that regard among G7 countries. They are simply guidelines, and while most builders adhere to them, the fact that the authorities don’t force them to indicates a curious lack of will that is difficult to explain, but a recent article in Shukan Playboy News made an attempt by comparing Japan’s insulation standards to those of Germany, which has the strictest in the world.
An engineering professor tells the magazine that maintaining a certain temperature for 100 square meters of interior floor area in a house built to Japanese insulation standards requires seven times as much kerosene as maintaining the same temperature for the same floor area in a house built to German standards. And that’s using the 1999 standards, which only apply to 10 percent of all homes in Japan as of 2023. About 70 percent of Japanese homes were built using insulation standards implemented in 1980, which, of course, are less stringent than the ones implemented in 1999. Then there are still homes standing that have no insulation at all.
That’s why Japanese houses are “naturally” cold, says the engineer, a situation that is actually illegal in many other countries. In the UK, for instance, a landlord is prohibited from renting out a residence if the uniform interior temperature falls below 18C. Also, in many countries landlords cover utilities, so it’s in their interest to maintain high energy efficiency. In Japan, it’s up to the tenant.
So why doesn’t Japan have stricter insulation standards? One reason is the commonly held prejudice that Japan is a hot country, so traditionally homes were built to maximize ventilation for hot, humid summers. Because of the draftiness of old Japanese homes, heating in the winter was done on a room-to-room basis. Nowadays, few Japanese live in traditionally styled houses, but the idea of cooling or heating individual rooms still holds, only now people use stand-alone heating units and wall-mounted air conditioners.
But the main reason for poor insulation standards, according to the professor, is economics. A prime indicator in Japan of economic health is new housing construction, and anything that is perceived to be a drag on new housing construction and sales, such as stricter design standards, is considered “damaging to the overall economy.” Of course, the government does mandate design standards for some structural elements, earthquake-proofing being the most well-known and probably successful. (The recent disaster in Noto is pretty good evidence, since almost all the homes that were destroyed or heavily damaged were built before the standards were implemented.) Some years ago the Cabinet decided that insulation standards should be made mandatory by 2020, but later the construction ministry vetoed the decision, saying that it would place a heavy burden on small and medium-sized developers and house builders, who would not be able to compete with larger, more experienced companies, and that would have a bad effect on the economy as a whole.
The only thing that has made the government reconsider insulation standards is international pressure to reduce emissions, which Japan has pledged to do. Consequently, the Cabinet has again decided to make insulation standards mandatory starting in 2025. The professor points out that 80 percent of new houses and 70 percent of new rental units being built now adhere to the 1999 standards, and when these standards become mandatory, most likely the central and local governments will provide subsidies for existing homes to upgrade to them.
But how strict are these standards? Each country has its own classification regulations for insulation. In Japan, the target standard is known as Class 4 insulation, which means that when the outside temperature is 0 degrees C and the room temperature at night in 20C, after all heat sources are extinguished the room temperature does not fall below 8C by the time the sun comes up. Class 5 insulation means the room temperature does not fall below 13C by morning; Class 6, 16C, and so forth. (For comparison’s sake, northern European homes tend to be pretty airtight, and thus lose almost none of their heat overnight when heating sources are extinguished.)
The professor says that Japan would need to mandate Class 6 standards in order to fulfill its carbon reduction obligations, but right now Class 4 is the standard. In Tokyo, that means fiberglass wall insulation that is 10 cm thick, ceiling insulation that is 20 cm thick, and double-glazed windows. As the professor points out, windows are the main points of heat loss, and in order to upgrade from Class 4 to Class 5, interior aluminum sashes should be replaced with resin sashes. To upgrade to Class 6, both interior and exterior sashes should be resin. Triple glazing also provides more efficiency.
A two-story house built to Class 6 standards would only require one heat pump-style air conditioner per floor to maintain a comfortable temperature all year round, and yet when he says this to new home buyers he usually gets a skeptical reaction because people are so conditioned to think that you need an aircon for each room of the house. What he tells them is that while resin-sash windows cost about ¥700,000 more than aluminum for a standard one-family house, the buyer can make up that amount by purchasing fewer air conditioners. In the long run, that also means lower energy bills, so the savings are compounded.
Unfortunately, there isn’t much to do about existing houses whose insulation standards are already low because it would mean opening walls and ripping out windows. The best thing to do would be to install a secondary set of interior windows and hanging “insulation blinds” that create an air curtain between the windows and the interior to maintain room temperature, much the same way a down jacket maintains body temperature.
Still, it’s unlikely that people who live in poorly insulated homes in Japan are going to make such renovations, mainly because home improvement here isn’t pursued for the sake of property value, which brings us to a related issue. You don’t have to be an economist to figure out that Japan’s aforementioned policy of pegging economic health to new housing construction is the main reason behind the problem of akiya, or vacant homes, of which there are 8.5 million. During Japan’s accelerated growth era after the war, this housing strategy made sense, but not any longer, especially with the population shrinking. And yet, new housing still figures prominently in the government’s economic planning. But another reason there are so many akiya is poor building standards, which render homes junk after a few decades. For many, even home improvement won’t make them worth anything, because the basic design was conceived with sellability in mind, not longevity or even livability. So Japan’s insulation problem is related directly to the akiya scourge, since it’s a side effect of an economic growth scheme that doesn’t look to the future, not even the immediate future. I want to buy this house as cheaply as possible right now. I’ll worry about whether it’s comfortable later.
Cat Foreheads & Rabbit Hutches 
comment on installation of uchi-mado, interior windows — in our basically solid condo across from Showa Kinen Koen, with great views, but 14 year old, we installed interior windows over already plain thick glass, across the full width facing the park. ordered from YamadaDenki, product was YKK-AP [YKK the sash co. and AP, Asahi Polymer] double pane with Argon gas between layers. intial cost installed was Yen620.000. then duction of Yen260,000 thanks to JP govt energy saving credit. makes a substantial improvement in heat retention, big reduction in outside noise and sun glare and summer heat. pleased with result and final cost. aesthically nice natural wood finish on the frames.
LikeLike
Are they difficult to clean?
LikeLike
window cleaning seldom needed as the veranda has a deep overhang that protects the area.
LikeLike
Japan isn’t the only country with houses that have poor insulation.
Our first house in Queensland had no insulation in the walls or ceiling.
Many people may think that Queensland is warm to hot all the time, but it does get quite cool in winter.
We used our fireplace often in winter and the A/C almost everyday in summer.
So I insulated the ceiling and after that we couldn’t use the fireplace as the house would get too hot. The A/C was used, but the house cooled down quicker and stayed cool longer.
It was a miserable job up in the. ceiling as the standard batt size was too small for the area between the joists. I had to cut batts to fit. In addition, the builders left a mess up there when they built the house and never cleaned up. IIRC that house was about 4000 square feet in size so the job took a lot of insulation and quite a bit of time.
We moved before we could really recover our investment in the insulation.
Our next two houses were rentals as we hadn’t decided what to do.
The first was a brand new house built in 2000. This house was in Melbourne and it had zero insulation as well. In summer the walls were so hot that you could feel the heat coming into the house. Cheap, quickly built, and typical of houses put up then. No A/C in the house either.
The next house was also a rental and it may or may not have had any insulation in it. If it did, it was the minimum amount. The house was a two storey house and in summer the second floor was so hot during the summer that you couldn’t sleep at night. We had to have an A/C put in two be able to live there.
The house was supposedly a high grade spec home built in 2003, but was again a cheaply built piece of crap. Everytime someone walked around on the second floor you could hear them downstairs as the floor would creak. When it rained hard the kitchen would flood.
Our current house had insulation in the ceiling when we bought it, but nothing in the walls and nothing under the floors. The windows are cheap, single pane glass. However the house was well built with quality materials and of all the houses we have lived in it is the most comfortable.
We had three hot days in row last week withe temp hitting 38C on the last day. We only needed to use the A/C for about an hour on that day to cool the house down for the dog.
That being said, in winter the house can get quite cool when we have continuous cloudy days with low temps.
And we pay a higher price for natural gas than people in Japan. Some of the new price contacts work out to A$37 per 1000 cubic feet of gas. So we can’t afford to heat the house at night. At 3000 square feet in area the house is now too big for us.
Lastly, the price of insulation here has skyrocketed since COVID hot and is now two to three times as much as before.
LikeLike
Japan isn’t the only country facing the conundrum of how to implement insulation standard. Doesn’t Beijing have some national program about insulating the homes of the poor. And I think the UK have something like that too, but I remember that they gave the money to the developers, who didn’t put any insulation in place anyway and just pocket the money.
LikeLike
The “hot country” argument is ridiculous. People don’t “maximize ventilation” in summer, they close the windows and run the air conditioner all day. There is a misconception in Japan that insulation only has effect in winter rather than being a thermal break. In the summer, it also keeps the home cool. Had this conversation with my wife’s brother and his wife. They are both Class-1 architects, but when they built their house, they put minimum insulation in it. He said to me, “This is Kyushu, not Hokkaido, so there is no reason to insulate to the Hokkaido standard.”
LikeLiked by 1 person
I think the professor in the article was talking about traditional Japanese houses–kominka, that kind of thing–built before air conditioning, which didn’t become widespread in Japan until the 80s.
LikeLike
Very interesting article!
I live in Taiwan and summers are miserable here: extremely hot and humid (probably even worse than Japan given that Taiwan is a bit more to the South).
I’ve read a lot about housing insulation online, but usually it focuses on insulating the house from outside cold (because it’s written for people in Western and Northern Europe, mostly). It looks like a well-insulated house is good both to keep warm during the winter, but also to keep cool during the summer.
However, if there is any good way to insulate a house from the humidity? In Taiwan, I feel the biggest issue is the humidity. I can tolerate 28 or 29 °C at night if it’s very dry, but when it’s humid, it’s unbearable…
That said, the buildings in Taiwan are really bad when it comes to insulation standards. They’re all concrete ovens with single-glazed windows, and everyone just blasts AC in every room for months on.
LikeLike
Excellent content as always. Thanks you!
LikeLike
The biggest technology difference with windows starts at the frame–a thermal break. After that, you get benefit from adding more panes. Resin is less conductive, so slows thermal bridging, but Japan also used to have very nice, very efficient window frames in aluminum or wood with a thermal break. Guy at YKK told me that the added 3% made them unmarketable without any regulatory enforcement.
Second problem (seen a lot with Tokyo architects) is a general arrogance about domestic vs. imported technologies. Frequently designers will oppose insulation–I joke not–as Western hegemony. The only way I can explain that outlook is to lump it with 1980s arguments about Japanese snow/ Japanese stomachs / etc. differing, science be damned. And very poor energy science education in the building professions.
LikeLike
Today’s Japan Times print edition has a story about hypothermia often occurring inside homes. Proposed solutions include wearing more clothes, holding hot water bottles, and eating more. Not even a mention of insulation.
https://www.japantimes.co.jp/news/2024/03/07/japan/noto-hypothermia-deaths/
When we built our home in Nagoya, by the way, I specced Class 6—roof, walls, and foundation—double pane windows with argon, and even central HVAC. Fireplace too, but that’s just for atmosphere.
LikeLike
Thanks for this. Quite amazing that there is absolutely no mention of lack of insulation.
LikeLike
Great article. I always enjoy my Cheap Houses newsletter. Thank you.
This topic is very relevant in todays world in respect to energy efficiency, building design (commercial and residential), climate change and the environment.
I lived in Japan, in 1989, Tokyo for 5 years and lived in a variety of housing both hot and cold.
The problem of poorly insulated residential homes is worldwide. I live in Australia, Sydney and our family business has been in the insulation industry for over 25 years. It is now mandatory to insulate new homes and renovations. The building legislations and codes are improving. However, I still see the lack of respect and probably the lack of knowledge at all levels of design and build in selecting the most appropriate insulation materials and products for the specific applications.
Fact: Australia has some of the most poorly insulated homes across the planet. For decades homes were built with no insulation. We are still retrofitting existing homes today. Ironically people moving to Australia will often comment during winter season “they have never been so cold in a home in their entire life.”
The flagrant disregard of the importance of building insulation materials and the lack of Government mandatory regulation and implementation into new buildings over the years has now come back to remind us of the significant impact that insulation materials have on the overall thermal and acoustic performance of a building.
I say it is the single most important building material you can include in the construction of a building – Residential, commercial or Industrial building. Far more important than any other building material. It turns a House into a Home.
Simply put ,Thermal Insulation material benefits the occupants of a dwelling on reducing their year round consumption of heating and cooling costs whilst improving the overall comfort levels not to mention reducing energy consumption and the environment.
In certain climates, air conditioning in conjunction with a correctly insulated home will definitely help with reducing summer humidity. Insulation does not stop humidity but it protects the envelope of the dwelling from heat gain and heat loss. Insulation will reduce the demand on air conditioners.
If it is at all possible to retro-fit insulation to a dwelling it will be a good investment and an immediate improvement on the thermal comfort – Health, Condensation, Mould etc. of the home for the occupants as well as their reduced energy bills.
Insulation is also climate zone and building design specific. Certain insulation materials will be more technically beneficial than others depending on the application (wall/floor/ceiling /roof).
Insulation is a big topic. Far more than just a Reply. There are a lot of insulation material types and many applications. Haven’t even started on window insulation yet! INSULATE – INSULATE – INSULATE !!!!
Seek out your local insulation expert. Know your building. Know your climate and then choose the correct insulation type.
Aim for COOL, WARM and QUIET
Duncan.
LikeLike