I am building a bath in the basement. I have I-beam type floor joist for the main floor. Can I run my exhaust pipe for the fan thought these joists? Thanks

I am on the verge of having a huge problem in my home. I'm a single mom with two kids and we live in an old mobile home. The Floor in my bathroom is rotting and and causing plumbing problems with my toilet too. My ex-husband was suppose to have taken care of the problem a few years back but did not do the job correctly and now I have a bigger mess than before. I know that when he took the floor out from under the toilet he was complaining that there was no brace under the toilet only the iron beams that come standard on a mobile home. Instead of trying to fix that problem he put the old floor back and just put in an extra peice of plywood to cover it up therefore the problem is worse. My question is (and please keep in mind that I am not a great carpenter) how do I go about ripping the floor out and adding new braces so that the flooring can be replaced and the plumbing fixed. I know how to do the vinyl flooring after the main floor is done but that is the only part I'm aware of how to do. Your help is much appreciated. :confused: