Then there are some shady construction practices going on. I'm pretty sure any self respecting building inspector would not allow 2x3s to be used for exterior walls as exterior walls are load bearing. 2x3s are not typically used in load bearing situations. I myself have never seen 2x3s used in that situation but 2x3s are common practice for some interior partition walls. I'm not saying you are lying. I'm just saying most areas do not allow that. Also the sponginess of the floor is probably because they did not properlybrace the floor system which normally are I joists. If they are not properly braced they can be spongy feeling.
jeremy
jeremy