Prevent structures from floating.

Hi!, im trying to create a mod that generates structures all around the world, but my problem is that some parts of the structure float (and that looks terrible D:), so, i've been thinking on a procedure to prevent this from happen, i came up with and idea, however i could not develop it (thats is why im asking for help). The idea is that, before the structure is generated, it is checked if there is a 15x15 area (x and z, and solid blocks), if it exists, spawns, if not, it does not.

any help plz? :D