3" pipe through joists

[Dan Morey]

I know there are a ton of threads about this, but I can't seem to find one that fits my situation.

The 2x10 floor joists supporting my bathroom span 15' at 16" o.c.. I doubled them up to reduce deflection for tile - glued and screwed them together. I rerouted my toilet and ran 3" pipe across 4 (double) joists, very precisely drilling a 3-5/8" hole, falling 1/4" per foot. While I did break the 1/3 rule, my drain pipe DOES fit within the 2" margin at the top and bottom of the joist. The bore is located approx. 24" from the supported end of the joist. I'm confident that the double joists make up for the 9/16" overboring. Where I'm not concerned is that I may put a vanity with a granite top directly over those joists, straddling the drain pipe essentially. My questions is really, when those bore/notch limits are calculated, what is the dead and live load assumed? If your live and dead load is much less than the limits, when would a larger hole/notch be acceptable?

I guess this is why we hire engineers, but the ones I've known in the past have been wrong.

 

[Cacher_Chick]

The couple of times I have seen it done, the engineers called for custom steel shoes which wrapped around the bottom of the joist.

 

[Sponsor]

 

[Jadnashua]

Most houses are built for a 10/40# dead/live load rating psf. The dead load includes anything permanently attached to the joists, which includes the subflooring, possibly cbu, and the tile, plumbing, ductwork, plus any non-load bearing walls, the tub, vanity, etc. It's really easy to overload the structure. The good thing is that there are probably millions of places similarly overloaded that haven't fallen down or cracked things. A wooden joist is similar to an I-beam, in that the tension/compression loads are mostly along the outside edges. This is why it is so bad to notch them, while boring them in the middle, isn't as detrimental overall.

As said, the safest thing is to talk to a structural engineer. When I was doing some remodeling, I talked to one guy that came out, ran some calculations, and gave me some advice. This was relatively cheap, but would have been much more if he had had to do any plans that he would have had to sign off on for the inspector.

 

[Winterson]

Even with a 400 lb. vanity with granite top load if it is a standard 24x72 inch vanity that is only 0.23 lbs per square inch. Now for a bathtub full of water where the total load is 600 lbs. before you add a person or two and I would be more concerned.

For purposes of both waterproofing and greatly reducing tile breakage putting down an uncoupling membrane over the subflooring is a good investment.