vent and drain questions

richardsamNovember 17, 2006

This is a remodel of a bathroom addition that was built on a patio in California. Questions are what size vent is required for the toilet, sink, and shower. The vanity will have a double sink. Can these vents be combined and if so does it change the diameter? The wet wall of this bathroom backs a drywall of another bathroom. The other bathroom has 3 vents ( I don't know why ). Could I tie the shower and toilet of the new bathroom into the 2" toilet vent of the other bath and the double vanity into the 2" vent for the double vanity in the other bath? The existing drains drop at about a 45 degree angle for about 3' to tie into the 3" main line. Is this acceptable for the toilet? Also all drains currently run off a 3" branch drain of the 3" main line. Should each drain tie in separately or is this branch line method acceptable?

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A double bowl vanity should only need a 1 1/2 in. vent, it should be o.k. to tie into a 2in. vent from the toilet as long as you make the connection 6in. above the flood level rim of any fixture connected to it.

A shower vent needs to be 1 1/2in., a toilet vent needs to be 2in. all the way, it can't be reduced, the same 6in. distance applies; using long distance engineering you should be o.k. with your proposal.

You can drain two toilets on a 3in. line where I work,[this is a local code call]. Best that I can do, lots of luck.

"If all else fails, read the directions"

    Bookmark   November 18, 2006 at 10:05AM
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With careful planning an entire bathroom group can be vented with one 1-1/2" vent.

Under the International Residential Code (IRC) all structures are required to have one "Main Vent" which must run undiminished in size from the bldg main drain through the roof. When additional auxillary vents are required they may be reduced to 1/2 the diameter of the line they serve but not less than 1-1/4".

By contrast, the California Code is primarily based upon the Uniform Plumbing Code (UPC) and the UPC takes a dramatically different approach to venting.

Under the UPC you are not required to have a "Main Vent" however the combined aggregate total of cross sectional area of all vents must be equal to or greater than the cross sectional area of the bldg main drain.

Under the UPC all vents must be computed by "Drainage Fixture Units"(DFU). A vent may be reduced to 1/2 the diameter of the line it serves providing that said vent meets the DFU restrictions of table UPC-T7-5.

To compute the vent size we must first determine the DFU load of the drain line or group of fixtures connected to the drain line.

Lavatory #1....................1DFU
Lavatory #2....................1DFU
Toilet(= or less than 1.6gpf)..3DFU
Total load...... 7DFU

Code minimum drain line size for a toilet drain is 3".

A 3" horizontal branch drain with a 1/4" per foor pitch can handle up to 35DFU's so there is no problem connecting all the fixtures to the same branch line.

Under Table UPC T7-5 an 1-1/2" vent is rated for a maximum of 8 DFU for a maximum developed length of 50'.

A toilet is required to be on the end of the drain line. Under the UPC a 3" drain line may then run a maximum of 6' from the toilet to the vent. The unvented section of line upstream of a vent to a fixture is defined as a "Fixture Arm". The line downstream of the vent is then classified as a "Vented Branch" or "Vented Drain".

You could connect an 1-1/2" lavatory drain line to the 3" branch from the toilet within 6' of the toilet, then connect an 1-1/2" vent from the lavatory riser up to the roof. This will provide the code minimum 1-1/2" vent to the 3" branch.

The UPC allows an unvented 1-1/2" fixture arm to run 3' 6" from trap to vent therefore you could connect an 1-1/2" line from the 3" branch to the tub drain at any convenient point downstream of the lavatory line and the tub will wet vent from the 3" vented branch.

While the tub is required to have an 1-1/2" drain opening we are also permitted to increase the size of a trap or drain line by one nominal trade size so you could increase the size of the tub trap and drain line to 2" and it could run 5' from the trap to the point where it ties into the 3" vented branch without any additional venting.

Thus, we have effectively vented the entire bathroom group with one 1-1/2" vent.

In regards to you question about the existing toilet vent run at a 45 degree angle. Code prohibits any horizontal vents which are below an elevation of 6" above the highest fixture served by the drain line however, in plumbing ALL lines which are greater than 45 degree above horizontal are considered a vertical line so that line is proper.

    Bookmark   November 20, 2006 at 9:38AM
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we have a wet bar in our kitchen that I found out was never vented we are getting a very foul order in the kitchen we have a double sink and a disposal in the kitchen along with the wet bar sink, could this be dangerous not just the smell of the fumes but could it combust? we are going to have someone look next week about putting a vent in for that bar sink in the mean time wondering if their is any danger? probally a stupid question but hey I had to ask

    Bookmark   August 6, 2007 at 2:31AM
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yep sewer gases are combustible.

    Bookmark   August 6, 2007 at 3:27AM
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After the kitchen sink water faucet is shut off there is a drumming/ gurgling noise. I suspect a drain vent issue. What are possible causes and fixes.



    Bookmark   August 8, 2007 at 4:43AM
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janey: Is this sink free-standing, i.e., not against a wall? It sounds like you might have an air admittance valve (also called a studor valve), which are allowed in some places where a conventional vent is difficult or impossible to install. Occasionally you'll also find them in a sink next to a wall where the installer did not want to hassle with installing a vent pipe. When these valves go bad they do release sewer gas. They are usually located inside the sink cabinet as far up as it can get. You might be able to fix the odor problem by replacing the AAV, or by installing a regular vent (loop type if the sink is out away from a wall, regular if not).

bobert: That could be a partial block in either the vent pipe or the drain pipe. You can run a snake down the vent pipe from the roof, as well as one down the drain after taking out the P-trap underneath the sink.

    Bookmark   August 8, 2007 at 5:44PM
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how far to the center of drain line off unfineshed wall for vanity sink,kitchen sink ?

    Bookmark   March 29, 2010 at 11:05PM
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When kitchen sink is drained after dishes are washed,(2 tub sink one filled halfway with water), washroom drain in basement girgles and sometimes water splashes up. Never noticed this before. We have just had 3 days of hard rain and i have had slow running sink in December. I snaked 3 inch drain in basement which runs away from washroom drain.

    Bookmark   March 6, 2011 at 10:08PM
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New water saving toilet. Bowl fills up and then most of it drains out. Water in bowl is very low. Is it the toilet or vent.

    Bookmark   February 11, 2012 at 3:11AM
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Open the tank and examine the fill valve. You will see a small diameter plastic tube that runs from the fill valve to the top of the standpipe. Make sure that line is properly connected so that all the water from that trap primer line is going into the standpipe. If so, the water level in your bowl is at the correct level for that style of bowl.

    Bookmark   February 11, 2012 at 4:42AM
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