Whatever happened to 3" vent stacks? I see new construction all the time where there are only 2 and 1.5 inch vents through the roof. There are 3 or 4 of them per home. And this is typical. 10 out of 10 (new) homes.
When I read the IRC I see so many requirements for a 3 inch vent that I don’t know what exception they are using to design the system this way. And all of our AHJ’s seem to accept this so there isn’t any pushback. In Colorado I should think we are concerned with small dia. pipes freezing over.
Can some of the plumbing experts please enlighten me on why we don’t have a 3" main stack (at least one) on homes any more? What exception and code in the IRC are they working with to design these systems?
Could you post those here?
You will see 3 inch stacks in territories that follow the UPC, not the IRC. I have been a licensed plumbing contractor in both jurisdictions.
Maybe this will help. This is from the 2018 IRC. The vent stack can be not less than 1/2 the size of the building drain. Most building drains are 3 inch.
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Martin, Thanks for challenging me on this. I needed that. This stemmed from a realtors husband who is a commercial HVAC engineer and he was showing me numerous references to the codes that referred to bathrooms as a unit needing a 3 inch pipe etc. I also see in the IRC where a 3 inch vent is required for frost closure (but I don’t think CO is in that temperature zone)
I guess I got caught up in that and the fact that most of our residential construction before the past 5 years or so does actually have at least one 3 inch pipe. I suppose I just took a few grains of fact and extrapolated the rest to come up with something that I thought was right.
Anyway, I appreciate you forcing me to dig out my own IRC book and get my facts straight. Have a great day and stay safe!
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Martin, I assume ‘building drain’ is the line from the home to the street?
Did a pre-drywall on a home today that was 4200 sf, 4 bath home.
It had 2 different 3" drain stacks that went under the slab, that I assume tied into the same 3"line to the street.
But the home only had one 2" vent. This is acceptable, correct?
Typically I see at least (2) 2" vents.
Daniel the building drain begins at any fixture inside of the building to the point at which the drain exits the building. The drain is called a sewer from this point to the sewer tap.
I often see one 2” vent on most of my homes. It’s too difficult to size the drainage fixture units to size the vent without more information.
I wouldn’t even attempt to try to size the venting for the house. That is beyond the scope of a home inspector and that’s the job of the plumber and the city in verifying all the DFUs work with the drain and venting system during the plan review stage and when the plumbing rough-in is done. Also, cheaper builders around here put one 2" vent to the roof and run everything else on an air admittance valve. Each bathroom group is vented through the sink’s AAV, kitchen sink goes to an AAV, etc. Builders on larger homes typically have 2 or more vents through the roof based on the plumber’s choice.
Correct, most of the home is vented with AAV, BUT, there is that pesky code issue, that they must have at least one exterior vent (or two).
This one seemed odd to only have one 2" vent, but 2 different 3" drain stacks in the home. (4 bathroom)