Large vent pipe up through 2 x 4 top plate

[Billy_Bob]

I want to install a large 4" vent pipe up through a 2 x 4 stud wall top plate and then up through the roof...

The wall in question is an outside bearing wall.

But code says you can only cut a 40% hole in a bearing wall. I assume this also means the top plates of a bearing wall?

Anyway what to do?

Can I go 4" through the roof, then Y or T in the attic to 2 or 3 smaller vent pipes which would then go through the top plate in 2 or 3 separate holes?

This is my house and I am doing all the work, so I can do what I want. So for example I have the option of adding a second 2 x 4 wall in front of the existing wall so I would then have a 2 x 8 wall and could drill holes between the two 2 x 4 top plates. Or whatever will work...

 

[TorontoTim]

First, how did the 4" waste stack get into the 2x4 wall in the first place? Where does it come from below? If it's coming out of the slab, it must be on the inside of any framed wall, otherwise it would be coming through the footing.

So far as routing it up the 2x4 wall and then through the roof, if you're willing to build another 2x4 wall in front of the existing one, then why not just a little bulkhead at the ceiling? Bring the stack out of the wall and up into the attic with a couple of angles hidden inside a bulkhead.

I don't know the code on splitting your 4" stack into multiple 2" vent lines to get into the attic and out through the roof. Somehow I don't think it's kosher.

Is a 4 inch stack code in your area? Some allow 3 inch, but still too big to come up through a 2x4 plate - your 4" pipe is probably bigger than the 2x4 itself anyhow!

 

[Sponsor]

 

[-Christopher]

2x4 lumber is only 1.5"x3.5"...

Find a convienient place to bump out or fur out the wall 4" so that you don't destroy the support in your structure.

(side notching more than 1/3 of the width into lumber also will cause structural issues.. always drill through the center 1/3 of a board.)

 

[Terry]

I think they are concerned with the studs.
I can pretty much cut the plates all up.
It's not uncommon with a 3" ABS pipe, that is 3-3/8" OD, to just cut the plate out. It does look nicer with the 3-9/16" selfeed though,
not much left of the plate though.