What is 床下? (picture attached)


Most detailed definition I could find:

> 床下とは  
>  建物の床の下。えん（縁）のした。

Picture from google:

[![enter image description
here](https://i.stack.imgur.com/Yd3J0.jpg)](https://i.stack.imgur.com/Yd3J0.jpg)

Example:

> その大雨で床下30センチまで水につかった。  
>  The heavy rain flooded my house up to 30cm below the floorboards.

However, what I don't understand from the above is:

Does the water rise within 30cm distance of the wooden floorboards (upper
limit) or 30cm above the cement floor (lower limit, like on the picture)? Does
床下 refer to the whole space? In any case, **what exactly happens in the
example sentence?**




Upper limit.

Though 床下【ゆかした】 stands as a noun by itself, it literally means "under-floor".
Therefore, 床下30センチ always means "-30cm from the floor level". 床 in this phrase
is understood as the floorboards you live upon. If you want to tell you have
30cm deep water in the space between the base and the floorboards, you have to
say 床下 **に** 30センチ (so that you grammatically treat 床下 as a noun).

Similarly, 床上【ゆかうえ】 is used for "above the floor level" as well.

Or more generally, there are lots of words with ～上/下 that means "(distance)
above/below _X_ ".

  * 桁上【けたうえ】/桁下【けたした】 _above/below the girder_ (see the pic)
  * 股上【またがみ】/股下【またした】 (of bottom wear) _rise / below the crotch_
  * 地上【ちじょう】/地下【ちか】 _above/below ground_
  * 氷点下【ひょうてんか】 _below freezing_ (= minus degree Celsius)

* * *

[![enter image description
here](https://i.stack.imgur.com/TSuhx.jpg)](https://i.stack.imgur.com/TSuhx.jpg)

* * *

**EDIT**

"床下 + number" is possibly open to two ways of interpretation (see the
comments)... But at least I've found [a J-E dictionary
entry](http://dictionary.goo.ne.jp/je/77294/meaning/m0u/) that says:

> 床下10センチまで水につかった  
>  The flood waters rose to within ten centimeters of the floor of his house.




Upper limit.

Though 床下【ゆかした】 stands as a noun by itself, it literally means "under-floor".
Therefore, 床下30センチ always means "-30cm from the floor level". 床 in this phrase
is understood as the floorboards you live upon. If you want to tell you have
30cm deep water in the space between the base and the floorboards, you have to
say 床下 **に** 30センチ (so that you grammatically treat 床下 as a noun).

Similarly, 床上【ゆかうえ】 is used for "above the floor level" as well.

Or more generally, there are lots of words with ～上/下 that means "(distance)
above/below _X_ ".

  * 桁上【けたうえ】/桁下【けたした】 _above/below the girder_ (see the pic)
  * 股上【またがみ】/股下【またした】 (of bottom wear) _rise / below the crotch_
  * 地上【ちじょう】/地下【ちか】 _above/below ground_
  * 氷点下【ひょうてんか】 _below freezing_ (= minus degree Celsius)

* * *

[![enter image description
here](https://i.stack.imgur.com/TSuhx.jpg)](https://i.stack.imgur.com/TSuhx.jpg)

* * *

**EDIT**

"床下 + number" is possibly open to two ways of interpretation (see the
comments)... But at least I've found [a J-E dictionary
entry](http://dictionary.goo.ne.jp/je/77294/meaning/m0u/) that says:

> 床下10センチまで水につかった  
>  The flood waters rose to within ten centimeters of the floor of his house.

