住chicago area, old house with low craw, I think basement best, good for basement and ( high)craw to check and fix any problems, howerer, if 房子下 面和周围 是 密致土壤(水不易渗下),周围易发水,craw might be better, survey houses around house u are interested in??
Re "但是这样不是basement更好么,可以当作一个buffer,缓冲一下啊。 不用就是了 。" This is true based on my research about radon. Since radon is heavy, it tends to concentrate on the lowest level. I wonder whether crawl space can have the same effect.