wood used under tatami mat

I will be replacing the wood under my father-in-laws tatami mats in a room in his home in Fukui. I hope to find out what kind of wood is under them and what kind of nails are holding them down. The reason being is that I would like to be as knowledable as possible before leaving Seattle USA.
Also does anyone know of a place that rents tools by the day in Fukui?
I am an experienced carpenter in Seattle and would like to know if there will be much difference in construction methods in Japan

They are ordinally, common and rough lumbers, so cheap. Under them, you will see the bare earth soil. If it is a very old and traditional house, no nail used (nail did not exist). Once they used hinoki (wood) as pilars (very rich people). Modern and ordinally wooden houses are used nails, and are not quite better constructed (mainly, because of high labor cost, shorter construction term, lower construction technics and lower quality materials. (that means that no young Jap people want to take a hard job, which needs lots of patience). The difference between Jap and US wooden houses is, mainly, with anti-earthquake structure or not. Examples. Horyuji or daibutsuden.

I'm a complete amateur when it comes to tatami. But are you really just replacing the "wooden" part of the tatami? That doesn't make sense to me. Are you sure you're not replacing the most consuming part which is the woven grass "igusa" sheet, and reforming the whole thick foundation which consist of layers of two or three different material?

In any case, in Japan, usually anything concerning tatami is usually handled by a tatami craftsman and not carpenters, so I hope you will be able to collect the necessary information as well as the special material and tools. Perhaps it is best to get in touch with your father-in-law's local tatami shop so that you can collaborate rather than to do it all by yourself. Again this has been an amateur pov.

For reference, I found a website with some tatami layer photos, but I don't have the ability to translate all the material names into English.
http://www.imix.or.jp/tatami/kouzou/kouzou.htm

Good luck, and it's a nice thing you're trying to do for him.

The inch thick tatami mats consisting of the foundation and sheet aren't "nailed down" to the house. They are just placed in order tightly next to each other. Up to a few decades ago, residents used to take out the mats by themselves and dried it for a day upon the great cleaning on new years eve. Also, note that desposing the old foundation can be complicated as it will be considered as industrial waste. Some people throw it away illegally causing a social problem.

Uco,
I think Kevin was asking about the wood used *underneath* tatami mats, not the core inside them (which is usually synthetic foam these days). Obviously it would be best to let a tatami dealer repair or replace the tatami mats themselves, but what the tatami are laid on is the work of a carpenter... which is where Kevin comes in. No idea what is underneath most tatami floors, though, as our apartment has only wooden flooring. I would have thought that the construction and type of wood used are going to vary quite a bit depending on the age and type of house.

Yes, I thought that's what Kevin meant, but it doesn't make sense to me to just replace that thin piece of beniya-ita when the important part is either the igusa or tatamidoko. Anyway, hopefully Kevin will solve that problem by himself.

Oh, and I don't think it's "earth" that's right beneath the mats. There is a sort of floor or whatever you call it. Otherwise you can't fit the mats tightly together. There is also air between the earth and the foundation of the house.

I am in fact only replacing the wood floor that supports the tatami mats. The tatami mats themselves were take outdoors to air out and my father in law found the wood floor under the mats to be in need of replacing because of weak spots. Any info in regard to the subfloor would be appreciated. I will need to remove the weak/rotted wood and replace it with an appropriate subfloor. Is 1'' plywood available in Fukui?

I will make the job happen once I get to Japan but would like to be as prepared as possible.
Thank you all for your input.

My wife tells me she remembers when the house was built that there is about a one foot of air between the floor under the mats and the earth. My guess it that there are floor joists, supporting the subfloor boards. In America those would be 2"x 10" every 16" on center, when a room spans 12'
" means inch
' means foot

Thanks for the follow-up, Kevin.

I just found a website that tells you "how to make tatami" and it's got English info!
http://www.tatami-mat.net/goza.html

Maybe you can email the webmaster for ideas on Fukui shopping.

I don't know about Seatle, but I think the major difference between L.A. (I lived there) and Fukui (have relatives there) is that Fukui like most of Japan has humid summers, and Fukui in particular has very cold, cloudy and snowy winters. A lot of American items tend to catch mold in Japan, while a lot of Japanese items tend to break from dryness in say L.A. I learned at elementary school that Japanese houses are built shifted from the ground so that humidity won't go directly into the floor.

Uco, Kevin is not replacing ANY part of the tatami mats. Kevin is replacing the floor (as in the actual structure of the house) of the tatami room.

If I was you Kevin I would assume that the floor is fairly similar to western ones, you can only have joists so far appart before the floorboards start to sag. And I would also assume that the wood used in most houses would be cheap lumber, but I'd go with some that has been run through a surface planer or it will catch on the mats and they will need to be replaced more frequently. I'm sure your carpentry skills will be perfect for the job.

In any case, I truly hope Kevin's father in law and his home was same from the recent flood in Fukui. Best regards.

I don't know the first thing about carpentry but what I can say is : We replaced the wood under this room when we first moved in due to weak spots , what we replaced it with is like a light color on the outside with different layers, I think maybe 5 layers , of different colors ... so looking at the wood from the side it was like ;
Light
Dark
Light
Dark
Light

Maybe around 1 - 1.5cm thick.
I remeber that the wood , when fitting it , had to go UNDER the door frames ( there is a gapjust big enough for around 1cm of wood to go under it. The wood sheets were supported by several beams of strong wood underneath, which turned out were almost deliberately spaced just right to fit one sheet on top of each rectangle.

Oh yea! and on older houses watch out for snakes residing underneath. Aspecialy in the winter.

Good luck with that!

I know this is not exactly what Kevin is looking for, but it does tell a lot about the structure of the "yuka-ita (floor)" under the tatami. It's in Japanese, but perhaps your wife can tell you the gist of it.
http://www.rakuten.co.jp/niigataseiki/425287/523858/

Here is a carpenter's term dictionary for reference.
http://www.imix.or.jp/bookmen/xindex1.html

You can probably find more Japanese info by searching �ô‚̉º�b�°”Â(under tatami|floor) on a Japanese search engine.

A site mentioned that you need to restructure a large part of the floor if you want to change the room from Japanese style (washitsu) to western style (youma), so it may be quite different from an ordinary western house.

Thanks go out to all of you that offered info on the floor repair under the tatami mats.
The floor joists spaced every 12 inches were 1 3/4inches square. the wood that went on top of that was mahogony plywood that was 1/2 inch thick. The plywood was about 75 inches long by 35 3/4 inches wide. I used 13 sheets of plywood in two rooms. As it turns out most Japanese rooms are measured by the number of tatami mats. I also replaced several floor joists. One problem I ran into was the plywood went under the sliding doors which were byfold screen doors that ran on a clear cedar or fir base that was connected at the corners of the rooms. I could not see any way to remove it without damage. so I had to hold my cuts a few inches away from the edges and then when I replaced the plywood I put an extra piece of wood under the seam and screwed it into both sides with screws. made it much stronger than the original seam. My father in law was a wonderful man who I felt happy to help.
Once again thanks all of you for the input.
Regards Kevin

I am from America and want to install a traditional tatami floor in my new home. what goes under the mats? Just a wood floor? I have no idea and cannot find any directions in English. Please e-mail me if you can help. I am so interested in the Japanese way of life and would also appreciate any places I could visit online to learn more about your culture. Thank you again for listening.

mark@torrentrecords.com

Tatami mats just sit on top of a regular floor. In Japan their techniques are different than ours. If you want to do a tatami in the traditional manner. just buy tatami mats and lay them out. Japanese rooms are exactly sized so the tatami mats go wall to wall. so it depends what size your tatami mats are and how many and the way you lay them out. What ever turns you on in regard to pattern. I have seen them many ways. let me know what you are thinking you want.

The book Japanes Homes and Their Surrounding by Edward S. Morse, first published in 1886 is an excellent source of detailed information about construction techniques in Japanese homes...he gets into tatami mats as well. This book is still in print, I beleive.

I am installing a new washitsu heya in my home. I unfortunately need to trim one tatami mat to fit the space (long story..... wall cannot be moved). I want the whole floor to be tatami...so the ''use wood to fill'' idea is not an option.

How would I best do this? I am willing to ''screw up'' a mat trying if I have to. But a bit of ''education'' on this would help assure success.

Thanks.

.....john

JohnB
I am not Japanese but have a long interest in the culture and worked in construction in Europe, building new houses or repairing houses built up to several centuries ago.
ANYWAY IN JAPAN it is possible to buy rectangular and squares boxes about 1 foot high that have a (removable) tatami tops. these boxes are used as storage inside and make a Japanese style room inside a western style room. Of course you can place the tatamis right on the wooden floor. DO NOT cut one or more tatami mats to fit the room! the Japanese place pieces of wood (either boards or plywood underneath with either real wood or veneer on top) the whole thing the thickness of a tatami mat to bridge gaps between tatamis and walls (especially in new apartments where rooms are no longer sized for tatamis). I HAVE SEEN this wood "trim"--it can be one foot wide--on one side only of a room or two sides or even all around the room. I will try to find Internet sites to show you some ideas but it may take time