4 inch plumbing vent stack?

[BlueRidgeMark]

I've never seen this before. How about you?

I'm remodeling my bathroom. Stripped down to the studs. I just found the original builder used 4" PVC for a vent stack off the toilet.

WHY?? I'm not a builder, so I could be wrong on this, but I don't think code requires much more than 2" on a vent stack. Maybe 1 1/2"?

Why chop a top plate in two just to run 4"???

Oh, well, at least it's not a load bearing wall. It's been that way for longer than I've been here, so I guess it will stay that way.

 

[GG Woody]

There is a town around here that requires 4" *just* going through the roof, apparently the "hoarfrost" can plug a smaller vent.
Is this just venting the toilet? Not a macerating toilet or a sump? Must have been free pipe!

 

[BlueRidgeMark]

There is a town around here that requires 4" *just* going through the roof, apparently the "hoarfrost" can plug a smaller vent.
Is this just venting the toilet? Not a macerating toilet or a sump? Must have been free pipe!

Yeah, just a plain jane toilet. Lazy as these people were, I guess it was just what he had on hand. You would not believe some of the garbage I've run into.

How about an interior door "header" made of a single 2x4? Laid flat? Oh, and butted into the king stud on one end. No cripple stud to be found.

Why, yes, that was in a load bearing wall. Why do you ask?

 

[Whitenuckler]

I've never seen this before. How about you?

I'm remodeling my bathroom. Stripped down to the studs. I just found the original builder used 4" PVC for a vent stack off the toilet.

WHY?? I'm not a builder, so I could be wrong on this, but I don't think code requires much more than 2" on a vent stack. Maybe 1 1/2"?

Why chop a top plate in two just to run 4"???

Oh, well, at least it's not a load bearing wall. It's been that way for longer than I've been here, so I guess it will stay that way.


View attachment 340820

That is the main stack, and 4 inch should be used. The other fixture vents that join up are usually 1 1/2. Remember that stack might have multiple vents, and you don't want it to get plugged with snow ect. I have replaced cast iron pipe on one house. That's when you use a breaker. If you have any amount of new plumbing going in, go to ABS.

 

[BlueRidgeMark]

Interesting. It's just the toilet, shower, and bathroom sink. That needs a 4"? There's a kitchen and another bathroom, but they both have 1 1/2" vents of their own.

Snow can be stopped with a vent cover, or is that not allowed?

 

[bholler]

Interesting. It's just the toilet, shower, and bathroom sink. That needs a 4"? There's a kitchen and another bathroom, but they both have 1 1/2" vents of their own.

Snow can be stopped with a vent cover, or is that not allowed?

They often ice up in our area if we have single digit or below temps for to long. And yes for just a bathroom 4" is probably excessive. I usually ran 2" just for a bathroom. But there are formulas to figure out how big it needs to be.

 

[BlueRidgeMark]

Well, thanks for the feedback! 👍

It's always good to learn something new!

 

[Whitenuckler]

Interesting. It's just the toilet, shower, and bathroom sink. That needs a 4"? There's a kitchen and another bathroom, but they both have 1 1/2" vents of their own.

Snow can be stopped with a vent cover, or is that not allowed?

Sometimes it is not easy to vent your plumbing to the main vent, although in a new design it should be done that way. In additions ect, they may have to run a new vent up and out. The "cheater" vent has also been used. I stuck one up under my kitchen sink after the trap. You should not need to cover a vent, as it should have warm sewer air coming up all the time. Now a 1 1/2 may plug up a bit for awhile. I have never in my life seen a cover for a plumbing vent. Plumbing is actually very interesting. The codes may be different in the warmer zones too.

 

[gthomas785]

I've never seen a main stack smaller than 3", and 4" is pretty common here. If it's venting a toilet it should be at least 3".
It also depends on the length of the run. Longer runs need more cross sectional area.

 

[Whitenuckler]

I've never seen a main stack smaller than 3", and 4" is pretty common here. If it's venting a toilet it should be at least 3".
It also depends on the length of the run. Longer runs need more cross sectional area.

I was thinking more about this venting. I believe the minimum size pipe for a toilette is 4 ". That needs a lot of air to get it where it needs to go. My old 1940's house was a cast iron 4 inch stack, a 2 level house, plus full basement. I think there was only one bathroom on the main level plus a roughed basement toilette in the laundry.
Later on a reno, they added a toilette to the main level, and had to run a vent all the way up to the second floor, past the drain for the bathroom up there. Then I added a toilette/tub/sink to the basement which was another venting master class. I had a good plumber on that as it was getting complicated. Venting is twice as hard as drains.

 

[gthomas785]

Yeah, venting trips up a lot of would-be DIY plumbers. Mainly because people think "water flows down" and don't think about what the air in the pipes is doing.

I believe, at least here in the states, the minimum drain size for a toilet is 3" and the vent needs to be the same size as or larger than the drain. There are other cases where you can have a smaller vent but I don't know the details

 

[Whitenuckler]

Yeah, venting trips up a lot of would-be DIY plumbers. Mainly because people think "water flows down" and don't think about what the air in the pipes is doing.

I believe, at least here in the states, the minimum drain size for a toilet is 3" and the vent needs to be the same size as or larger than the drain. There are other cases where you can have a smaller vent but I don't know the details

I agree. When a DIY'er (which I am one) looks at their drain pipe, they can't even see the venting network of pipes past the trap.
It needs to be studied, and get a plumber who knows all this. Can be very important in the lower levels of your house. If you add a drain in the wrong place you might fill up your vents and use them as drains. That is allowed I believe in certain cases, but not good.

 

[BlueRidgeMark]

the vent needs to be the same size as or larger than the drain.

I could understand requiring the same size, but larger? That makes no sense at all. Air flows more readily than water. A given size of pipe will allow more air to flow than water.

And since many homes have 4" drains on toilets, larger would be 6" (unless somebody makes 5" DWV pipe?)

 

[gthomas785]

Ok, you're right, I misremembered the rule. The vent has to be at least half the diameter of the drain served, and the size goes up depending on what fixtures there are.

Looking back at your photo, that appears to be a 2x4 wall. Is that correct? A 4" pipe (with 4.5" outside diameter) would not fit inside the 3.5" space so I'm guessing it's a 3" pipe which would make a lot more sense. Unless the photo is playing tricks on me and the wall is made of 2x6.

 

[Whitenuckler]

Ok, you're right, I misremembered the rule. The vent has to be at least half the diameter of the drain served, and the size goes up depending on what fixtures there are.

Looking back at your photo, that appears to be a 2x4 wall. Is that correct? A 4" pipe (with 4.5" outside diameter) would not fit inside the 3.5" space so I'm guessing it's a 3" pipe which would make a lot more sense. Unless the photo is playing tricks on me and the wall is made of 2x6.

The Ontario Building Code | Vent Stacks, or Stack Vents

The length of the vent is calculated too.