Can I cut through a top plate?

[Pronouncedeyen]

I'm running a 2" PVC drain pipe from one room to the next to connect to the main stack. The most convenient height (plumbing-wise) for it to pass between the two rooms is through part of the top plate of a load bearing wall. It's an old house so the top plate is made of 2 actual 2x4s. The top of the drain pipe lines up exactly where the 2 2x4s meet.

Can I cut through the bottom 2x4 to run the pipe? If so, do I need to reinforce that 2x4 from underneath somehow?

 

[Dana]

If there is a joist or rafter resting on the section of top plate more than two inches from the nearest stud it's better to leave it alone, or beef it up by lagging in some angle irons or plate steel or something to stiffen it up. If nothing is resting on that section between stud or the joist/rafter very close to the stud, you'll be just fine.

In "optimized value engineering" or "advanced framing" techniques the top plates of studwalls are single 2x, but all rafters & joists get aligned directly over the studs.

 

[Sponsor]

 

[Leejosepho]

As mentioned, the double plate is there to hold the load of overhead floor joists or roof rafters or trusses or whatever, and you should be fine as long as you do not disturb it beneath an actual point of load between any two studs. But if you have floor joists there (like for the second floor of a two-story house), you will likely not have any load-free spaces between studs. So in that kind of situation, I would likely add 2 x ? x 14-1/2" blocks above the plate and between that joist and the others on either side, then cut only as much as necessary from the bottom part of that plate (if I have heard you correctly) for getting the pipe on through.

 

[Pronouncedeyen]

Thanks for the help leejosepho and Dana. Here's a picture of what it looks like.

The first floor studs line up right underneath the second floor studs. The joists are attached to the studs. I have some flexibility on where in between the studs I put the pipe (horizontally) but height-wise it needs to pass through the bottom 2x4 in the top plate. These are real 2x4s so there is a 12" distance between a joist and the next stud.

I'm planning to leave the top 2x4 intact so there shouldn't be any lateral movement issue. Would it make sense to put a 2x4x14 in between the studs slightly below the pipe? Or is that overkill? A 2" PVC pipe is actual 2 3/8" wide so I guess I'd have to put a couple thin pieces of wood in between the bottom 2x4 in the plate and my 2x4 so it's actually supporting the weight.

 

[Leejosepho]

If there is a joist or rafter resting on the section of top plate more than two inches from the nearest stud...

You are definitely within that parameter, pronounce, so you should be just fine. That joist places a shear load at the inside edge of the stud just below it and would not break that plate even if both pieces were cut.

 

[Tom Sawyer]

Simpson ties and full coverage steel nail/wall plates required top and bottom.

 

[Dana]

As sketched, you're fine as-is. It'll carry the load without any further reinforcement, since the load is carried very close to the axis of the stud below, with no framing element more than a couple inches from the lower stud.

If the joists or upper studs were somewhere in the middle of the span it would be a different story.

 

[Pronouncedeyen]

Thanks all for the great responses. This really is a great website.