Return to the Plumbing Forum | Post a Follow-Up

Toilet drain line through floor joists?

Posted by kirkhall (My Page) on
Fri, Jan 6, 12 at 0:16

I am in the planning for a remodel (and will be talking with a plumber soon). But, I was hoping I could get one question answered (this should be easy):

What size 2by joist is needed if you need to run a toilet-size drain pipe through it in order to get it to a drop wall (from second story to crawl)?

The toilet would be the only fixture on the run through the joists in this fashion (other fixtures would join in a joist-space near the drop).

I know needing to do this will add cost--having to cut holes for the drain line adds labor. But, I am just wondering how big the joist needs to be. (I have at least 2x10s, not sure if they are 2x12s yet (haven't crawled up there and moved insulation out of the way).

Follow-Up Postings:

RE: Toilet drain line through floor joists?

know this: many people forget to mention (or to think of) using steel flat bars as joist reinforcement. It's like sistering, but using steel. It's not a big deal to drill holes in steel.

Web search for cutting holes in joists. Or wait for a specific answer in the next post by anyone else.

R2E: Toilet drain line through floor joists?

forgot to mention: Remodeling experts know about joist strength and mechanical strength. The question is not a plumbing question, but some plumbers will know what the published guidelines are for cutting holes in joists.

Here is a link that might be useful: remodeling forum

RE: Toilet drain line through floor joists?

There are repair plates available for specific joist sizes for drain lines.

Anything much else can require an engineers stamp to satisfy the AHJ.

RE: Toilet drain line through floor joists?

Okay. Not as simple as I thought. Thanks guys.

(The joists in my case do not exceed 9 feet, since I am sure that will matter.)

answered on remodeling forum

In case anyone finds my post later, I got an answer on the remodeling forum as suggested by davidro1:

The code says board/3 at minimum, as long as you are at least 2 inches away from each side. So, a 2x12 is the minimum.

Hope I have that.

RE: Toilet drain line through floor joists?

You can also use smaller joists and then put an approved repair in them.

reRE: Toilet drain line through floor joists?

Look around here.

Here is a link that might be useful: Joist repair

RE: Toilet drain line through floor joists?

after you measure the outside diameter of the pipe, and then add a fraction for the hole to be bigger and to allow the pipe slope too, you may be over the limit of a 12 inch joist.

So start thinking about metal. If you buy 1/8" flat bar the inspector will see it is overkill compared to any sheet metal "repair kit". Is there an inspector? If so, consult him.

RE: Toilet drain line through floor joists?

All great advice.
Yes, I will have a city inspector, but depending on which one I get, I will be more or less confident in their "inspection". (I have to be honest and say, with our addition, one of them was much more thorough than another--who didn't go into the crawlspace to inspect anything, for example).

As for where in the span, it could go anywhere along the length of it, I believe. So wherever is best, we can do.

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Plumbing Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here