I suggest the translation above accompanied with the footnote:” Kaijian is used to describe the sectioning of a building across its façade, forming several parallel compartments throughout a building. Basically, kaijian compartmentalises a building into several vertical rectangles.”

Kaijian seems to be different from a room, which is defined as “a part of the inside of a building that is separated from other parts by walls, floor, and ceiling:” ( http://bit.ly/1bHr5fT ) The word “room” doesn’t convey the notion of how a house is compartmentalised across its façade. Also, as one kaijian section might contain several rooms, the two words don’t seem to be used interchangeably.

Thoughts/ comments are very welcome, as this is not really familiar territory for me.

Sources:
http://bit.ly/1ave4Ud : “The term kaijian is sometimes used synonymously with the single character jian in describing the horizontal compartmentalization or sectioning of building space across the façade.”

Looking at the diagram at the bottom right corner of page 22, the Northern China jian has 3 compartments and the Southern China jian has 3 compartments as well. However, the former is sectioned to form 3 spaces or rooms, whereas the latter has partitions in the middle of each jian, forming 6 spaces or rooms.

http://www.douban.com/note/221078869/ : Please refer to the diagram with the caption 五开间建筑开间及进深结构示意图

http://down6.zhulong.com/tech/detailprof237964JN.htm : This villa has 三开间 (three kaijian). When you look at the layout, kaijian seems to refer to how the house is compartmentalized across the facade, with three parallel kaijian sections running vertically. However, this house has more than 3 rooms, as several rooms can exist within a kaijian section.

http://down6.zhulong.com/tech/detailprof699221SN.htm


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Note added at 19 hrs (2013-10-19 08:38:01 GMT)
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Correction: The following para should read “Looking at the diagram at the bottom right corner of page 22, the Northern China three-jian building and the Southern China three-jian building both have three vertical rectangular compartments.” However, the former is sectioned to form 3 spaces or rooms, whereas the latter has partitions in the middle of each jian, forming 6 spaces or rooms.

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Note added at 23 hrs (2013-10-19 12:25:43 GMT)
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Oh no! I accidentally voted this as a non pro question with my smart phone (touch screens are tricky!) How do I undo this? Sorry for the inconvenience caused.