Plumbing – How to reinforce a joist with plumbing running through it


After removing the sub floor in my bathroom in order to extend the sewer pipe for the toilet (it's too close to the tank-side wall), I found that the floor joists have extremely large holes cut in them to make way for the plumbing.

What are my options for reinforcing them? I don't think I could do a sister joist both because of the plumbing running through the joist and because the joist runs quite a ways through the floor of my second story, and adding a sister joist would involve taking up a ton of the floor.

Should I brace it with steel bridging? I'm concerned about the potential vertical load.

What options do I have?

The room is approx 74" by 105" (the 105" runs in the same direction as the joists, it appears that the joists are at least that long, but may extend beneath other rooms)
Joists are 15/8 inches wide, 71/2 inches tall.
There is a 1st floor bathroom below. There is a tub in the 1st floor bathroom bordered by 3 walls – one of these walls runs perpendicular to the joists 4 feet away from the wall shown on the right in the first picture below.

holes in joists

You can see in this close-up that the furthest joist is completely missing it's bottom:
close up of hole in furthest joist

Best Answer

I had an electrician notch the top 5" of a 2x10 (9" old growth Douglas fir) in the middle of an 18' span.

I brought in a structural engineer and he said the 18' 2x10 was already over current span code limits without the 5" notch. He specified 3/4" continuous ply gussets nailed to each side of the joist extending 18" past each side of the notch. He allowed the gussets to only be the 4" height and fit under the notch.

In your case, you are not in the middle span, I assume this is the start of the joist?

The toilet rough in appears to have completely cut through the joist so there is no connection and it has been blocked to the side joist with a single 2x4 and a single nail.

You likely want to get a structural engineer to specify a prescriptive fix for this. A site visit and prescription is likely to cost less than $1,000 and be well worth it.

You might be able to sister with steel that is shallow and could sit above and below the plumbing penetrations and not need to be sistered the full length of the joist.