Size of hole for floor joist

[kdrymer]

We are building a house and on a recent trip to the house I was looking more closely at the floor joists and plumbing in the basement. I noticed this hole was cut in one of the 2x10 joists to accommodate a 3 inch schedule 40 PVC drain pipe for a bathroom toilet that is above this location. The outer diameter of 3 inch Schedule 40 PVC is 3.5 inches and you can tell from the picture that the hole is at least a half inch bigger than that so this is likely a 4 inch hole that was bored. I know this exceeds the specifications of having a hole no more than 1/3 the total depth of the joist (9-1/4" actual depth) and I already see small cracking (also can be seen in the picture) on both sides of the hole spanning most of the joist. The cracking is not very deep (at least yet!) and is not cracked on the opposite side.

What do you recommend doing in this situation? I really am not happy about it, and would ideally like some kind of brace plate installed to reinforce this area or perhaps have blocking installed perpendicular to the joist and create a box around this area. Maybe I'm overreacting and worrying for nothing? I know the size of the hole is not compliant but should I be concerned if the builder doesn't seem motivated to fix?

 

[bud16415]

I think it will be fine it is in the center and most of the stress is at the extreme fibers at the top and bottom. I have seen much worse.

Top compression, bottom tension.

Looks like a nice neat plumbing job with that pipe and also the PEX

 

[Flyover]

@bud16415:

In this case, doesn't wood at the top and bottom of the hole become "extreme fibers" as well? Why NOT install a plate to reinforce it, if it only takes a few bucks for the plate and a few minutes to install? (Or if not a plate, then sistering the joist, or some other reinforcement method)

 

[zannej]

I think I have seen hole plates for plumbing before. Mostly for walls though. Not sure if they are designed to fit for joists.
That pipe being in the very center and not being closer than 2" to the edge is not a bad thing.

 

[billshack]

What i tell plumbing contractors to do if they must cut a hole into a floor joists. Install 3/4 plywood with glue and screws to one or both side of the joist. wait one day and then drill away.

 

[bud16415]

@bud16415:

In this case, doesn't wood at the top and bottom of the hole become "extreme fibers" as well? Why NOT install a plate to reinforce it, if it only takes a few bucks for the plate and a few minutes to install? (Or if not a plate, then sistering the joist, or some other reinforcement method)

All designs assume factors of safety. Part of that safety factor assumes every piece or wood does not have the exact same strength and that floor loading distributes weight etc. There are reasonable exceptions that deal with plating and such as if say every joist in the floor was going to get a large hole all in a line. In this case it looks like one joist is being compromised and the two on each side of it are solid.



Sometimes they remove a couple joists in a area for a stair case and the double the ones outside it to add the strength back in. There is much about all these practices that is accepted as proper framing and one of the reason every trade now has to have an inspection before the next step goes on.



There is code and that doesn’t mean it can’t be built to surpass code. If the OP and the builder and plumber hash it out and it needs plated to make the homeowner happy the work that’s done could be taken out and the joists plated and the pipes redone. And the builder or the trade will have to take the hit.

I personally wouldn’t push it as it likely wasn’t in the plan.

 

[Flyover]

Thanks for that, @bud16415. It's eye opening for me to learn this stuff and how it goes from the perspective of the builders.

 

[kdrymer]

Thanks for the feedback. I had a chance to go out and measure and it is a 4 inch diameter hole on a 9.25 inch deep joist (nominal 2x10). There is approximately 2 - 5/8 inches of wood both above and below the hole. The minor split that may be visible in the picture is only on the outer surface (at least right now) and is not penetrating deeper inside the holes. The area that is above this location will be a toilet and walk in shower to the right of it in the picture.

There is blocking on both sides of the hole (not seen from the picture) to provide extra shear strength for the pre-cast foundation walls (Superior Walls) similar to the attached diagram. I would think this may help provide extra support for the floor in this area...

I did find a two-piece metal plate (link below) that can be used in places where there is existing plumbing (up to 6" diameter) running through the joist that is supposed to provide extra reinforcement. The high number of screws required makes me wonder if its worth doing this though..

https://joistrepair.com/products/2810hr

 

[Jeff Handy]

I would contact your local building inspector about it, and email or text them the pic and the measurements.

Personally, I would request the double plywood sistering with glue and screws.
Even if you have to pay half the cost.
You will sleep better at night.
And your shower pan won’t sag or crack.

 

[kdrymer]

Fair enough, just figured I was gather some general advice.

 

[bud16415]

If you are really worrying about it I would do something similar to what @Jeff Handy suggested above. Cut out 4 pieces of ½ plywood the width of the joist and long enough for some attachment on both sides maybe 18” long. Then with a saber saw cut a U shaped cutout that has half the hole as the bottom. Put two on each side facing opposite directions and use white glue against the joist and between pieces. Clamp all 4 up with two C-clamps and put a few drywall screws in to hold it while the glue dries.

If the builder wont do it DIY after you move in. It is a simple DIY method that won’t require removing the pipes. You will have to pull the PEX back to do it by pulling off the two plastic nail clamps.

 

[Jeff Handy]

I would just cut two 3/4 plywood pieces, three or four feet long.
Full 9 1/4 inch height of the joist.
Then cut a U shaped cutout to accommodate the drain pipe.
But cut one to install on one side with the U facing up, the other on other side with the U facing down.
Glue and screw as stated before.
And put the pex back up as stated before.
This way the plywood is reinforcing the whole height of the joist, and the weak spot that is already splitting, right across the middle of the hole.
What either piece misses, the other piece picks up.

If you want to get nutty, you could even glue two pieces to fill in the gaps in the U cutout, but just for looks.

 

[bud16415]

I would just cut two 3/4 plywood pieces, three or four feet long.
Full 9 1/4 inch height of the joist.
Then cut a U shaped cutout to accommodate the drain pipe.
But cut one to install on one side with the U facing up, the other on other side with the U facing down.
Glue and screw as stated before.
And put the pex back up as stated before.
This way the plywood is reinforcing the whole height of the joist, and the weak spot that is already splitting, right across the middle of the hole.
What either piece misses, the other piece picks up.

If you want to get nutty, you could even glue two pieces to fill in the gaps in the U cutout, but just for looks.

LOL Thats because you have a pile of 3/4" scrap plywood and i have a pile of 1/2"

Both methods sound good. Now we need a welder to chime in on the two piece of angle iron method with thru bolts as he has a pile of 2" angle iron pieces.

 

[Flyover]

Funny enough...

We closed on our house today and took the kids on a little drive to go see it. I was in the basement envisioning the gym when I looked up at the exposed joists and noticed there are a full two rows of holes in them. Granted, the holes are probably 1" in diameter, maybe 1.5". But they are all lined up, with conduit and wires and stuff going through them.

 

[bud16415]

Funny enough...

We closed on our house today and took the kids on a little drive to go see it. I was in the basement envisioning the gym when I looked up at the exposed joists and noticed there are a full two rows of holes in them. Granted, the holes are probably 1" in diameter, maybe 1.5". But they are all lined up, with conduit and wires and stuff going through them.

Be glad they did it that way and didn't hang them below. Congrats on the house.