Expert: Richard Taylor, AIA - 4/1/2010

Question
My parents are having their upstairs bathrooms renovated and enlarged in their home in Wisconsin.  For these renovations, the main plumbing wall containing the stack (which runs parallel to the joists) was moved about 4 feet.  The plumbers ran, in addition to several smaller holes, a 3.5" stack through the joists.

The joists are nominally 2x10s,with an additional 1.5" of flooring products to be placed upon them.  The joist span is approximately 13' and all of the holes (new and old) are largely within the center third of the joist span.  In addition, to accommodate the slope of the stack through the floor, some of the holes cut in the joist are only 1.5" - 2" from the bottom.

My concern is whether these joists (3-4 in total) need to be reinforced because of these alterations?  And if so?  What is the best way to go about doing it, now that the plumbing has been installed?

Thanks for your help.

Answer
Chris - thanks for your question!

Yikes!  The plumbers did EVERYTHING wrong!  Whatever you do to repair the structure, you MUST have the plumbers pay for it.

The greatest amount of "moment" stress in a floor joist is generated in the middle third - and at the bottom, as you've suspected.  That's why building codes restrict notching and hole-cutting to outside the middle third, and then limit the number, size, and location.

Problem is, it's going to be tricky repairing the damage and keeping the plumbing in place.  You can't just sister a new floor joist alongside the existing, you'd have to cut holes in it also.

Exactly what needs to be done requires a thorough analysis of the loading on the joists, but you may find that you need to lower the ceiling in the room below in order to add the necessary structure.

You may have room to run new engineered-lumber beams in between the bad joists - the new beams could be less deep than the floor joists and might allow room for the pipes underneath.  No way to know without seeing it.

If the load's not too great, you can reinforce the bottom of the bad joists with steel strapping.  But don't just run out to Home Depot and buy plumbing straps, have an engineer size the proper remedy including the attachment pattern.  The right kind of straps are probably going to be from Simpson Strong-Tie.

Alternatively, you can (at the plumber's expense) remove the plumbing work, install new floor joists alongside the old, and have a new plumber route the pipes properly.  That is the best course of action!

Hope this helps,

Richard Taylor, AIA
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