The IRC says if you stay at least 2 inches from the top and bottom, the largest hole allowed is the actual joist depth/3 so the short answer is the joists will need to be 2x12's which is unlikely for a 9 ft span but you might get lucky.

Thanks Renovator. (I hope I am lucky. :) )

Or just use a sheet metal repair unit on a smaller joist.

I just posted on the plumbing thread. About using flat bar to reinforce.

kirk you also need to post how far from the joist end the hole will be. Too close is not permitted, because the weight of the floor rests on the joist ends resting on something else.

We would be able to cross the joist wherever along its length was structurally "best". I don't believe we will have a limitation on that.

instead of crossing the pipe diagonally in the middle of the floor, it is best (for the drain pipe) to cross right where the toilet is: the "closet bend" under the toilet would go straight to the joist. So, in terms of distance from the joist end, where is the toilet' closet bend now?

There is not a current toilet in the space. Here is my proposed layout:

The dotted line running E-W between the Master and the hall bath is a beam supporting the floors--used to be an exterior wall downstairs.

The only place for a down drain is along the exterior wall (W wall) of the proposed hall bath--at the end near the drawn hall bath toilet (not at the end near the Master bath Toilet. The joists run N-S in this area.

The circled S is the location of the current stack for the house/downstairs bath. In this plan, I think the hall bath vanities can be drained to either the toilet lines and W, or to the old stack.

The Master bath sinks and shower would require a much smaller down line (what are those called, anyway?), and could more easily be dropped down the W wall again. (under all this space is an open great room).

You need DWV design help. This is because you wrote that the hall bath vanities can be drained either ... or... (which is not true in a well-designed DWV system). Depending on where the whole-house outlet is, your choice will be clear.

It's a different question from the one about reinforcing a joist or two. At http://www.terrylove.com/forums/forum.php you can get help with DWV. Draw North and South on your diagram.

My mistake. It would be best to send the hall bath vanities to the old stack. Our house used to have a septic out the south of the house. Then, before we purchased it, it was converted to sewer, which is in the street (north).

North and South are true to the orientation of the picture, North up, and South down.

Thank's for Terry's forum information.

Prefabricated sheet metal reinforcement is usually limited to one unit per 2x10 or 2x8 solid sawn No. 2 Southern Pine joist with a clear span not exceeding 15-0 for 2x10âÂÂs and 12-0 for 2x8âÂÂs with the center of the hole more than 12â from a support. Other smaller holes must be at least 20 inches away. The maximum hole diameter is 6 inches in 2x10âÂÂs and 4 1/2 inches in 2x8âÂÂs.

This kind of reinforcement is recognized by building codes but adding a strap would usually need an engineer's stamp.