Japanese winter home insulation hacks

Pro-tip: central heating and insulation that actually keeps your house warm.

it beats huddling around the heated toilet seat in the winter.

We went with spray foam style insulation when we built our house at the northern edge of the Kanto Plain, where the winters aren't particularly harsh. This morning it was minus three. The insulation isn't particularly effective, unfortunately.

But, everything is double glazed, and a gas heater on the bottom storey and one A/C set to heat on the second keeps it comfortable, but not cozy.

Insulation is not only effective for trapping in heat in the winter, but also the cool air-conditioning in summer. It’s so much more energy efficient.

I really can’t get over the lack of insulation in homes in Japan. I thought it was only an issue in older apartments. But I bought a newly-built home in 2020 and it’s the same. I work from home. My work space is a 6-jo sized room. I have the heat pump on and the door shut, I wear a heat tech base layer, a sweatshirt, a vest, and wrap myself in a blanket. That keeps me warm, but it shouldn’t be required.

Last time I visited Canada, I was comfortable wearing a t-shirt indoors.

carp_boya,

Do you know what kind of insulation it has? I'm just curious because our spray foam isn't very good, but I don't know if it's because it's too thin, in the wrong places, the wrong choice for the wrong house design ( we had a lot of input into the design) etc. It doesn't work that well in summer either.

Hokkaido-level insulation throughout the country plus central heating. Isn't it obvious?

Build a tiny home, double layer window facing an open-field to the south, AC on 18, with floor heating heated from local electricity generation. My electricity bills around 8000yen at worst.

House is warm all winter, and cool all summer.

It's possible if you don't bring your "North American" mentality to Japan.

Well, instead of providing poor 3rd world country advices on how to get warm indoors, how about building the houses properly, with proper insulation and central heating like the rest of the developed countries.

Japan is the only so called developed country in the world, who still builds houses like a 3rd world country, with wood and cardboard walls (unbelievable, I know).

Not to mention ZERO insulation, zero sound proofing and almost zero confort due to very small shoe box size of rooms.

"Japan's insulation standards are Class 4, Class 5, and Class 6, which specify the minimum room temperature that must be maintained after the heat is turned off."

Class 4: The room temperature should not fall below 8°C by morning if the outside temperature is 0°C and the room temperature is 20°C at night

Class 5: The room temperature should not fall below 13°C by morning

Class 6: The room temperature should not fall below 16°C by morning

Class 5: The room temperature should not fall below 13°C by morning

That's us, I guess. Below zero this morning and a thermometer in an empty bedroom upstairs reads 13.3.

Good info, wallace. Thanks.

We went with spray foam style insulation when we built our house at the northern edge of the Kanto Plain, where the winters aren't particularly harsh. This morning it was minus three. The insulation isn't particularly effective, unfortunately.

That's a shame. We have a house with closed cell spray foam ("koushitsu uretan" in Japanese) and it is super toasty. It is so airtight that the front door is hard to open when the kitchen extractor is on. We heat 50 square meters on two floors with one 14 mat coldzone aircon. We're in the mountains in Nagano and it regularly gets to minus 8 to 10C, and colder if there is radiative cooling on a clear night.

If your house is 13C in the morning after a night of no heating, that's actually very good. Improving it beyond that level will involve a huge jump in build cost, with a payback in energy savings of 50 or possibly even over 100 years. The only reason to do it is increase comfort.

Move to Okinawa

kohakuebisu,

Thanks. Much appreciated. We'll leave it as is and do a bit more research next time we design and build a house. I.e., never.

Your house sounds rad. Well done.

The cost of paraffin/kerosene is now equal to the price of electricity. Since last year we stopped using it and do not have to go outside for refills. Besides the AC we use small but very effective ceramic heaters for local heating.

It’s absolutely pathetic that people have to mess around with bubble wrap and what not in a supposedly modern country in 2024.

In winter I take off the bug screens to allow more sunlight in through the big south facing French windows. This heats up the whole house.

I’m on the beach until Valentine’s Day though so not really a problem for me at the moment.

When I lived in the cold hills of Nagano we used big styrofoam sheets to cover the windows at night.

They were cheap and really good at keeping the heat in.

Old, cheap aluminum Japanese windows are the worst culprit in poorly insulated homes.

Most of our rooms start off at 6 degrees in the mornings. If I light the kerosene/paraffin stove in the kitchen it'll get up to 7 or 8 degrees in about half an hour, then pretty quickly it'll even go over 10 degrees. Wallace's Class 3?

The wife is itching to turn it off, however, if I leave the room for any reason. She says she's plenty warm; it's only because I want it that the stove is even on, unless she is using it for heating the kettle or cooking.

There are plenty of well heated well insulated homes around if one looks. People just do not want to prioritize this choice and seem to love the seasonal drama

If you cannot have 72 all year at a reasonable bill - something is wrong

Just bought some insulation at a Daiso today; goes against the full-length glass doors, with suction cups. We'll see in the morning.

Get a house built in an area where sunlight is in good and constant supply. My house has nothing in front of it so we get sunshine almost from sun up to sundown. Makes a big difference in the overall warmth and with heating costs in the winter.

Energy efficiency is great, but is only one aspect of building a house. To make a house superinsulated and avoid thermal bridges (places where you have framing only without insulation) and simple gaps in your insulation, such as the curly eaves on a traditional Japanese roof, the easiest way is to use a very simple box shape with no bump outs or recesses or architecturally interesting features to facilitate wrapping the outside in unbroken insulation. Efficiency also says you can have big windows facing south for solar gain, but should have minimally sized windows on other sides to avoid heat loss. If you get too far into this, you can end up with a boring or quite ugly house that forsakes the views of that cherry tree or over the park to the north just so you can save 5000 yen a year on your heating bill. That's not a very good tradeoff. You may find your budget allowing a small superinsulated house, or a larger one that still very well insulated and has bedrooms you can fit a big bed in. Efficiency should be a priority, but not the only one. If your roof or anywhere on your land faces south, you can make more than plenty of energy with solar panels.

Getting back to the story, but the government is currently offering big subsidies for uchimado (secondary glazing). They make a huge difference. The subsidy is called "mado rinobe" and could pay 2/3 of the cost of window upgrades depending on how big most of your windows are. If you are renting, by all means do what you can with bubble wrap, but it is definitely not the best approach for a house you own.