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Discussion Starter · #1 ·
1) The plumbing codes state that when it is necessary to increase the size of a vent extension through the roof that the change in diameter must be made at least 12 inches inside the building below the roof. What is the purpose of this rule? Why can't the change be made at 3" inside the building?

2) The codes state that the diameter of the vent stack cannot exceed the diameter of the waste stack to which it connects. What is the purpose of this rule?

3) With this next question, I am not interested in hearing that it is a ridiculous waste of resources (I have my reasons) - I just want to know if it will be allowed by code and if it will cause any problems with the intended function of the waste/ventilation system. I am building a 6000 sq. ft. one story home. The main waste line has been installed and is 4" diameter. All fixture vents will be 2" and will be dry vents extending up into the attic. My plans have always been to tie all 2" vents at one end of the house together into a 4" double sanitary tee. This will be accomplished in the attic by tying individual 2" vents into a 3" vent which will then be tied into one inlet of the 4" tee. A couple of the single 2" vents will be directly tied into the other 2 inlets of the tee. A 4" pipe will exit the roof. This setup will occur at each end of the house. Therefore, two 4" vent pipes will exit the roof. Is this setup allowed? Will it cause any problems? Is it possible to have too much ventilation?
 

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1. This is required in cold zones so that the vent does not ice shut due to freezing condensation
2. Never heard that
3. Vent requirements are complicated sometimes and different inspectors will ask for different things. What code will you work with.
 
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1) The plumbing codes state that when it is necessary to increase the size of a vent extension through the roof that the change in diameter must be made at least 12 inches inside the building below the roof. What is the purpose of this rule? Why can't the change be made at 3" inside the building?

2) The codes state that the diameter of the vent stack cannot exceed the diameter of the waste stack to which it connects. What is the purpose of this rule?

3) With this next question, I am not interested in hearing that it is a ridiculous waste of resources (I have my reasons) - I just want to know if it will be allowed by code and if it will cause any problems with the intended function of the waste/ventilation system. I am building a 6000 sq. ft. one story home. The main waste line has been installed and is 4" diameter. All fixture vents will be 2" and will be dry vents extending up into the attic. My plans have always been to tie all 2" vents at one end of the house together into a 4" double sanitary tee. This will be accomplished in the attic by tying individual 2" vents into a 3" vent which will then be tied into one inlet of the 4" tee. A couple of the single 2" vents will be directly tied into the other 2 inlets of the tee. A 4" pipe will exit the roof. This setup will occur at each end of the house. Therefore, two 4" vent pipes will exit the roof. Is this setup allowed? Will it cause any problems? Is it possible to have too much ventilation?
1- sizing is needed to prevent the opening to freeze over from condensation in cold areas..2- don't know where you heard that Don't believe it..3- vents are sized to the proper fixture unit they serve..inspectors can be picky..before you install your vents as you discribe call the inspector handling you area run it by him 1st...
 

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Discussion Starter · #5 ·
Got number 2 from: Craftsman Plumber's Handbook by Howard C. Massey 1998 edition and third printing in 2002. Found in on the web through Google. Just re-read this part. It states: "It's OK to upgrade a plumbing system by using larger vent pipes - as long as the vent pipe doesn't exceed the diameter of the soil or waste stack it serves."
 

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The plumbing codes state that when it is necessary to increase the size of a vent extension through the roof that the change in diameter must be made at least 12 inches inside the building below the roof. What is the purpose of this rule? Why can't the change be made at 3" inside the building?

In cold climates, vents must be protected from freezing. Condensation can collect on the inside of the pipe. In cold climates this condensation can turn into ice. As the ice grows the vent becomes blocked and useless. By making the increase 1 ft it helps protect the pipe from freezing.

2) The codes state that the diameter of the vent stack cannot exceed the diameter of the waste stack to which it connects. What is the purpose of this rule?

This one I just don't know. Taking a guess I would think it would be for too much draft and noise whistle noise. Just not sure

3) With this next question, I am not interested in hearing that it is a ridiculous waste of resources (I have my reasons) - I just want to know if it will be allowed by code and if it will cause any problems with the intended function of the waste/ventilation system. I am building a 6000 sq. ft. one story home. The main waste line has been installed and is 4" diameter. All fixture vents will be 2" and will be dry vents extending up into the attic. My plans have always been to tie all 2" vents at one end of the house together into a 4" double sanitary tee. This will be accomplished in the attic by tying individual 2" vents into a 3" vent which will then be tied into one inlet of the 4" tee. A couple of the single 2" vents will be directly tied into the other 2 inlets of the tee. A 4" pipe will exit the roof. This setup will occur at each end of the house. Therefore, two 4" vent pipes will exit the roof. Is this setup allowed? Yes

Will it cause any problems? No Is it possible to have too much ventilation? No[/quote]
 

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Discussion Starter · #7 ·
THANKS to everyone for their quick and intelligent answers! This is indeed a GREAT site! I have read a lot about plumbing for about a year now but recently found these items through a Google search for something else and was beginning to wonder if I was totally lost. By the way, I have a licensed plumber who is going to inspect everything and is the one who installed the in-slab plumbing.

If anyone else wants to add anything, feel free to do so.
 

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2) The codes state that the diameter of the vent stack cannot exceed the diameter of the waste stack to which it connects. What is the purpose of this rule?




If you increase the size of the vent over the soil service line, you can end up with auto siphon action, this would happen on windy days, the air rushing over the vent creates a vacuum in the system this would cause this action and could pull the traps dry. This is why you cannot go over.
 

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The siphon thing makes sense: if water has to travel faster to move the same volume through a narrower tube the same would be true for air. I heard another plausible explanation: If a foreign object enteres a 3" stack from the roof, theoretically it should continue to fall through the system as it continued through the same 3" tube or a bigger 4" tube and be washed through the soil line like anything else. If a foreign object falls into a 4" stack from the roof, it may be big enough to lodge it's self when the diameter decreases to a smaller 3", killing the vent.
 

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The Standard Plumbing Code.
There's no such thing. UPC is probably most common, but there are others, and multitudes of varying rules by locality. I built my own house a couple of years ago. It is plumbed per IRC 2003, which addresses differently than the UPC. All of my vents are tied together, and only the 4-inch waste stack penetrates the roof. It's a log house with a metal roof, and I didn't want to see a bunch of vent pipes sticking out of it.
 

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If I had to guess (assuming that it came out of a codebook, but i've never heard it before either) #2 would be to prevent "cheating" the cross-sectional area rule.

Other than that, I see no mechanical reason why or why not, aside from having to cut a bigger hole in your roof with a bigger pipe going through it. But hey, if you want to try and find a 12" roof jack, be my guest. :jester:
 

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Discussion Starter · #13 ·
Code states: You may not install a vent terminal for a sanitary system within 10 feet of any door, window that opens, or ventilating opening, unless it extends at least 3 feet above the top of that opening. I don't intend to do this but was just wondering if a bathroom exhaust vent was considered a ventilating opening since it is for exhaust purposes?
 

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Discussion Starter · #14 ·
Alan, per your statements:

"If I had to guess (assuming that it came out of a codebook, but i've never heard it before either) #2 would be to prevent "cheating" the cross-sectional area rule.

Other than that, I see no mechanical reason why or why not, aside from having to cut a bigger hole in your roof with a bigger pipe going through it. But hey, if you want to try and find a 12" roof jack, be my guest."

As originally listed by me:

2) The code states that the diameter of the vent stack cannot exceed the diameter of the waste stack to which it connects. What is the purpose of this rule?

Not sure what you mean by: "#2 would be to prevent "cheating" the cross-sectional area rule". Since the rule states that vent pipes can't be smaller than the cross-sectional area of the sewer, the larger the vent pipes (not smaller) the better they would meet this particular rule.

Also, not quite sure why you would need a 12" roof jack?
 

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If I had to guess (assuming that it came out of a codebook, but i've never heard it before either) #2 would be to prevent "cheating" the cross-sectional area rule.

Other than that, I see no mechanical reason why or why not, aside from having to cut a bigger hole in your roof with a bigger pipe going through it. But hey, if you want to try and find a 12" roof jack, be my guest. :jester:
Again the reason for this rule is the venturi principle for plumbing.. plumbing design 101
If you increase the size of the vent over the soil service line, you can end up with auto siphon action, this would happen on windy days, the air rushing over the vent creates a vacuum in the system this would cause this action and could pull the traps dry. This is why you cannot go over.
 

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Again the reason for this rule is the venturi principle for plumbing.. plumbing design 101
If you increase the size of the vent over the soil service line, you can end up with auto siphon action, this would happen on windy days, the air rushing over the vent creates a vacuum in the system this would cause this action and could pull the traps dry. This is why you cannot go over.
So, you're saying I can't use a 4x4x6 combo to vent my building drain? :jester:
 

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So, you're saying I can't use a 4x4x6 combo to vent my building drain? :jester:
If you’re venting off the 6 you can’t go 8 if off the 4 you can’t go six that you cannot vent 6 on 4 soil at least not under our code. I took a course in plumbing systems design before I took my masters and this was one of the issues covered in the venting portion.
 

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Discussion Starter · #18 ·
Therefore, it seems to me you are saying that I should only have a maximum of one 4" vent out the roof in my situation. Is this correct? Anything larger would be just asking for problems?
 

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If you’re venting off the 6 you can’t go 8 if off the 4 you can’t go six that you cannot vent 6 on 4 soil at least not under our code. I took a course in plumbing systems design before I took my masters and this was one of the issues covered in the venting portion.
Can i go 5" on 4"? (only kidding) Seriously though, I'm trying to see how a plumber would oversize a vent like this-or why.
BTW, i don't recall anything like this in the UPC. I don't think it's covered but I may be wrong
 

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Discussion Starter · #20 ·
Javiles,

Thanks for a very intelligent answer. So let me just make sure. I should not vent a 4" sewer line with two 4" vents at the opposite ends of the line or I will be just asking for problems. Correct?
 
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