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We are almost to the mechanical stage of our remodel and the one thing that still has me confused (and always did) was plumbing vents. I understand the basic idea behind them but actually installing them is a different story.
My MAIN question regards tying them together somewhere and just venting out a single pipe. The 2nd floor will have 2 full bathrooms on it. Is it “wrong” to run a separate vent for tub, toilet and sink into the attic and tie them together up there? I haven’t really paid attention in attics too much but I don’t recall ever seeing a bunch of pvc piping up there except for the vent going through roof.
And my last question is, aside from possible problems with animal blockages, is it ok to vent out a gable wall instead of through roof?
 

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You have to go thru the roof

Thank you for the video. I still don’t understand why you must go through the roof. How it seems, as long as the stack vents higher then the water, the system will work properly. Am I missing something?
It is also about the gases leaving the sewer system. I don't know the rule but I am sure there is one. The reason for traps is about sewer gas.
 

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The plumbing code rules around how the upper end of the vent pipe terminates is mostly concerned with keeping the noxious gases distant. The link below is for the code where I live, but most North American plumbing codes are similar to a large degree (I’m assuming that’s where you live). Check out section 2.5.6.5 – Terminals (that’s how the pipe “terminates”). My interpretation of sentence 3 there is that you could run a vent out a wall, but it doesn’t do much for you because you would then have to run it up the outside of the wall to terminate above the roof anyway.

There are a surprising number of rules around the proper construction of vent piping, just the same as drain piping. The rules are significantly more complex that those concerning the piping that supplies the water to the fixtures. If you’re getting this work inspected (or if you just want it to work properly) it would be worth your while educating yourself on them. For example, when you tie those separate vent pipes together in the attic (which is fine to do), the size of the pipe needs to increase depending on the number and type of fixtures that the pipe is venting.

Chris

http://free.bcpublications.ca/civix... AND CIVIX_DOCUMENT_ANCESTORS:bcpc2018?1#hit1
 

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We are almost to the mechanical stage of our remodel and the one thing that still has me confused (and always did) was plumbing vents. I understand the basic idea behind them but actually installing them is a different story.
My MAIN question regards tying them together somewhere and just venting out a single pipe. The 2nd floor will have 2 full bathrooms on it. Is it “wrong” to run a separate vent for tub, toilet and sink into the attic and tie them together up there? I haven’t really paid attention in attics too much but I don’t recall ever seeing a bunch of pvc piping up there except for the vent going through roof.
And my last question is, aside from possible problems with animal blockages, is it ok to vent out a gable wall instead of through roof?
You can tie individual vents together as long as they intersect 6" above the flood rim of the fixtures served. Doesn't matter if it is in the wall or attic. As you connect to other vents, you need to maintain the proper sizing and lengths too.

If I follow the method laid out in my plumbing code, my state does allow vents to exit the gable in certain conditions. Check with your state, county or city code folks.
 

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It would be a great help to know what state you are in and what code you must follow.
Under IPC these are a few things that must be followed.


VENT TERMINALS
903.1 Roof extension. Open vent pipes that extend through a roof shall be terminated not less than 12 inches ( 304.8 mm) above the roof. Where a roof is to be used for assembly or as a promenade, observation deck, sunbathing deck or similar purposes, open vent pipes shall terminate not less than 7 feet (2134 mm) above the roof within 10 feet of the occupiable area.
903.2 Frost closure. Where the 97.5 -percent value for outside design temperature is 0°F (-18°C) or less, vent extensions through a roof or wall shall be not less than 3 inches (76 mm) in diameter. Any increase in the size of the vent shall be made not less than 1 foot (305 mm) inside the thermal envelope of the building.
903.3 Flashings. The juncture of each vent pipe with the roof line shall be made water tight by an approved flashing.
903.4 Prohibited use. A vent terminal shall not be used for any purpose other than a vent terminal.
903.5 Location of vent terminal. An open vent terminal from a drainage system shall not be located directly beneath any door, openable window, or other air intake opening of the building or of an adjacent building, and any such vent terminal shall not be within 10 feet (3048 mm) horizontally of such an opening unless it is 3 feet (914 mm) or more above the top of such opening.
903.6 Extension through the wall. Vent terminals extending through the wall shall terminate at a point not less than 10 feet (3048 mm) from a lot line and not less than 10 feet (3048 mm) above average ground level. Vent terminals shall not terminate under the overhang of a structure with soffit vents. Side wall vent terminals shall be protected to prevent birds or rodents from entering or blocking the vent opening.
903.7 Extension outside a structure. In climates where the 97.5 -percent value for outside design temperature is less than 0°F (-18°C), vent pipes installed on the exterior of the structure shall be protected against freezing by insulation, heat or both.
SECTION 904
OUTDOOR VENT EXTENSIONS
904.1 Required vent extension. The vent system serving each building drain shall have not less than one vent pipe that extends to the outdoors.
904.1.1 Installation. The required vent shall be a dry vent that connects to the building drain or an extension of a drain that connects to the building drain. Such vent shall not be an island fixture vent as allowed by Section 916.
904.1.2 Size. The required vent shall be sized in accordance with Section 906.2 based on the required size of the building drain.



905.2 Grade. Vent and branch vent pipes shall be so graded and connected as to drain back to the drainage pipe by gravity.



This is a very small portion of the venting code under IPC.
 
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