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BACKUP PREVENTION, SEPTIC
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BATH & KITCHEN DESIGN GUIDE
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DEPTH of SEPTIC TANK
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FAUCETS & CONTROLS, KITCHEN & BATH
FAUCETS, OUTDOOR HOSE BIBBS
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
FLOOR DRAIN / TRAP ODORS
FLUSHOMETER VALVES for TOILETS URINALS
GAS PIPING, VALVES, CONTROLS
GALVANIC SCALE & METAL CORROSION
HARD WATER - SOFTENERS
HEAT TAPES, Heat, Insulation prevent Freeze-Up
LEAD POISONING HAZARDS GUIDE
LEAD IN DRINKING WATER, HOW to REDUCE
METHANE GAS SOURCES
MIXING / ANTI-SCALD VALVES
MUNICIPAL WATER PRESSURE IMPROVEMENTS
NOISE / SOUND DIAGNOSIS & CURE
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ODORS, SEPTIC or SEWER
ODORS SEWER GAS in COLD WEATHER
ODORS, SULPHUR SMELL SOURCES
ANIMAL or URINE ODOR SOURCE DETECTION
PIPING IN BUILDINGS, Clogs Leaks Types
PLUMBING FIXTURES, KITCHEN, BATH
PLUMBING NOISE CONTROL
PLUMBING VENT DEFINITIONS & CODES
PLUMBING VENT DEFECTS & NOISES
PUMPS, WATER REPAIR
RELIEF VALVE LEAKS
RELIEF VALVES - TP Valves on Boilers
RELIEF VALVES - STEAM TP VALVES
RELIEF VALVES - Water Heaters
RELIEF VALVES - Water Tanks
REPAIR BURST LEAKY PIPES
METHANE GAS HAZARDS
SEPTIC SYSTEM INSPECT DIAGNOSE REPAIR
SHUTOFF VALVE LOCATION, USE
SULPHUR & SEWER GAS SMELL SOURCES
SWEATING (CONDENSATION) on PIPES, TANKS
TOILETS, INSPECT, INSTALL, REPAIR
WATER, WELLS, WATER TANKS: TESTING GUIDE
WATER PRESSURE LOSS DIAGNOSIS & REPAIR
WATER PUMPS & TANKS
WATER SOFTENERS & CONDITIONERS
WATER SOURCE ALTERNATIVES
WATER SUPPLY & DRAIN PIPING
WATER SHUTOFF VALVE LOCATION, USE
WATER SHUTOFF VALVE, WELL PUMP
WATER TESTS, CONTAMINANTS, TREATMENT
WELLS CISTERNS & SPRINGS
WINTERIZE A BUILDING
This article defines plumbing vent system terms, distances, and functions, and other specifications and code requirements. We explain how plumbing vents work on buildings, why plumbing vent piping is needed, and what happens to the building drains when the vent piping is not working.
We define the soil stack, waste stack, wet vents and dry vents, and we summarize the distances permitted between plumbing fixtures and their vent piping. We also explain how sewer gas odors m may be traced to plumbing vent problems. Contact Us by email if you are having trouble finding the information you need.
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Our page top sketch of a plumbing stack vent and other sketches included below are provided courtesy of Carson Dunlop Associates.
How & Why Building Plumbing Vent Piping Works
The plumbing vent system is part of the building plumbing drain system and serves two basic functions:
1. Allow building drains to flow freely by allowing air into the drain system, avoiding the vacuum and slow drainage that would otherwise occur at fixtures.
Now perform the same experiment, but punch a hole in the bottom of your soda bottle just before you turn it upside down. Because air can easily enter the bottle the soda flows nicely out of the bottle mouth.
2. Allow sewer gases to be vented safely outdoors. Because sewer gases may flow back up into the building drain piping from a public sewer or private septic system, and because some sewer gases are included in building waste flowing through the piping, the plumbing vent system needs to carry these gases outside, usually above the building roof, where they are disposed-of safely and without leaving unpleasant, or possibly dangerous smells and gases inside the building.
The basic plumbing vent terms are shown in the sketch at left. In these notes, the plumbing stack vents and other sketches included below are provided courtesy of Carson Dunlop Associates.
Here we show the main building vent pipe, the plumbing stack vent, connecting inside plumbing drains to a vent pipe that extends above the building roof in order to let needed air into the drains and to vent sewer gases harmlessly above the building.
Below we explain how building plumbing vent systems work and why plumbing vents are needed for drain function and plumbing drain safety.
Above the roof plumbing vent height: vent pipes should extend to outdoors above the building roof and should terminate vertically not less than 6" above the roof surface (nor more than 24") and must be at least 12" from any vertical surface (such as a nearby sidewall). (UPC (i) 906.1 and 906.2). Note that there are other restrictions: for a roof that is also used as an occupied space, for example, the vent has to extend at least even feet above the surface and be secured with stays.
Above roof plumbing vent diameter: in areas exposed to snow or freezing or temperatures below 0 degF., that can block a plumbing vent, the vent pipe should be at least 2" in diameter beginning at least one foot inside the building in an insulated space before the vent passes through the roof. Where there is a snow-cover risk (snow can block the plumbing vent) the vent should extend 24" above the roof surface.
The soil stack pipe, as shown in Carson Dunlop's sketch, carries waste from toilets to the house trap (if one is installed) and there connects to the sewer line extending outside the building and on to a public sewer or private septic system.
The soil stack is the large-diameter main vertical waste pipe or building drain, or vertical portion of the "main drain" in the building.
The soil stack pipe is normally extended outdoors above the building roof, as shown in the page top sketch.
Other main building drain piping sections that slope closer to horizontal are connected to the soil stack but move waste horizontally where needed in a building.
The waste stack pipe shown in the sketch refers to any other vertical drain piping in the building that does not carry soil (sewage) from a sanitary fixture (toilet). Typically waste stack piping carries drainage away from sinks, tubs, and showers.
As we discuss at DRAIN NOISES, if the horizontal distance between a plumbing fixture and the vertical vent piping is too great, the fixture may not drain properly, producing slow drainage or gurgling noises.
Poor drainage is not just an annoyance, it can be unsafe since there is also the risk that the poorly-vented plumbing fixture will lose the water from its plumbing trap, then permitting sewer gases into the building.
As we show in Carson Dunlop's sketch, the distance allowed between a plumbing fixture (actually the fixture plumbing trap) and the vertical vent piping varies between a minimum and maximum as a function of the pipe diameter.
Below our tables 1 and 2 summarize common plumbing code specifications for fixture venting and vent pipe sizes and distances that a plumbing fixture can be located (horizontally) from the vent stack. You'll see these distances also in our sketch at left. [Click any image to see an enlarged, detailed version.].
Within the building the plumbing vent routing is generally unrestricted. That is, dry vent piping carrying only air, sewer gas, or moisture to above the roof line is unrestricted. However the piping does need to be protected from nails - use nail plates to protect vent and drain piping both where where piping passes through studs, joists, or rafters.
Basically,larger piping diameter allows longer distances between a plumbing fixture and its vent stack. If a plumbing fixture is located too far from the main building vent stack, then its own drain pipe must have its own vent stack connection piping.
But if a plumbing fixture is close enough (five feet or less) to the main waste stack pipe (vent), the fixture does not usually require its own plumbing vent piping, and it is considered a direct-vented plumbing fixture.
Of course this rule presumes that the drain piping between the fixture trap and the waste stack is properly installed and properly sloped.
The usual slope on the fixture drain piping is 1/4" of slope per 12" (foot) of horizontal distance or "run" of piping.
In many buildings we find that the toilet is located quite close (within 5 feet) of the main building waste stack. This makes sense because the toilet needs really effective venting. Our sketch above shows a toilet located close to the waste stack - an installation that should work fine.
When you flush a toilet it sends a sudden large volume of waste and wastewater into the building drain waste vent (DWV) piping. This surge of wastewater can certainly create a vacuum problem in the waste line if the vent piping system is inadequate, blocked, or missing entirely.
It is exactly this condition that produces the gurgling or even siphonage out and loss of water in nearby sink or tub traps when you flush a toilet in a building where the vent piping is inadequate. See Plumbing Drain Noises.
A toilet that is located too far from the soil stack can be wet vented as shown in Carson Dunlop's sketch. The drain piping for a sink (basin) or other fixture located closer to the soil stack than is the toilet can provide a pathway to let air into the horizontal waste piping used by the toilet to carry waste to the soil stack.
But a wet vented fixture requires a larger drain pipe diameter in its wet portion as we show in the sketch. This diameter increase helps assure adequate air flow into the drain system in the event that the sink basin (in this example) happens to be draining at the same moment that the toilet is flushed. (908.2.3.)
Also note that wet vented fixtures (toilet, bathtub, shower, or floor drain) are permitted for bathrooms on the same floor level, not between floors.
The table below gives required clearance distances to various building features and cites pertinent model plumbing codes.
Plumbing Code Citations for Plumbing Vent or Vent Stack Clearance Distances
Quoting model plumbing code such as the IRC:
Plumbing Code Citation References
At PLUMBING DRAIN NOISES we explain the basics of proper plumbing vent piping and how errors cause trap siphonage, odors, and noises
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Frequently Asked Questions (FAQs) about plumbing vent installation, definitions, & clearance distances
Question: can the soil stack curve above ground to avoid a wall?
I am trying to find out if the soil stack can be curved above ground because there is a wall that I need to move. The wall will moved about 1 1/2 feet and the soil stack is currently inside the wall that I desire to move. This is in Portland, Oregon. The pipe that was used for the soil stack is cast iron, but I want to change this to the black ABS. Are there restrictions to how much the pipe can be curved? - Enan
Take a look at the UPC (see citations in the article above or at "References" below. Certainly I've seen plenty of soil stacks (vent piping) that were not straight runs in above-ground (or above building) routing.
Actually the part of the pipe that I wanted to curve would be down in the basement below the water closet (toilet, sink, and shower)There is only 1 restroom in this house. This means that the part that is curved would be under load from all the water draining from the sink, toilet, and shower. I was trying to avoid tearing up the concrete floor to install new drainage pipe and also because of how close the soil stack is to the cement wall in the basement.
The basement is not a full basement, but about a quarter of it is still crawl space which has been framed, and drywall installed (its used for storage). The soil stack runs next to this wall that is half concrete half drywall. My plan was to cut the soil stack about three or four feet above the concrete floor and then do a 45 degree turn until the pipe enters the drywall portion of the partitioned wall and then have it go straight up to the roof. Do you know if that might cause a problem with the pipe being under load from the drainage of the water closet? I planned to change everything above the cut that I make into the cast iron pipe with ABS. Of course I would brace everything that needs to be braced.
Question: Can a sink and toilet share the same waste line and vent?
Can a sink and toilet share the same waste line and vent? - Jim
Reply: Yes but ...
Jim: yes vent piping can be shared, but all fixtures need to meet the distance requirements.
Question: drain trouble in a new house - bubbling lower floor toilet and slow drain
I just moved and seem to be having trouble with the drained in the new house. When someone is in the shower upstairs air bubbles come from the toilet downstairs. If you try to flush the downstairs toilet the water will not drain. Just wondering if anyone knows what the problem might be and what I can do about it. Thank you. - Lucas
Question: one sink drains slowly and doesn't seem to clear - could it be a vent problem?
All the sink and toilets drain great in the house but one sink in the upstairs bed room. I have ran a snake, many times pipes are clean. Drain will handle water slowly. But if I fill the sink open the plunger or even take it out, it take an extremely amount of time to drain Could it be the dry vent if so, How Do I Clean it Thank you for you time. - Larry Miller
But his work did not help open the drain one iota. Later we began tearing open the wall to remove and replace galvanized iron drain piping. When I removed a short horizontal drain section in the wall between the sink and the main drain line, it was apparent that that section of piping was nearly 100% blocked by rust and iron deposits. The "wire snake" had just passed through that little opening but had not helped a bit. Really the only fix for that condition was to replace the piping. There was too much solid deposit to clear with a snake or with drain cleaner.
Follow-Up Comment: Derek Plumber offers more advice on clearing a blocked drain
A snake does not always completely clear a clog, blockage depending on how long it has taken to build up the blog, blockage can mean a difference in how you approach. Of course start with a snake the issue u have with it still draining slow is most likely that as you have gone through the clog, blockage and pulled the snake out that the Black Tar is just collapsing back on itself thus making it nearly impossible to clear with a snake.
If you have it draining slow this means that you have only cleared a path through the clog, blockage and that the issue is still there and will eventually blog up again.
You can try running your HOT water slowly while using your snake in a back and for motion many times over attempting to pushing what breaks free and is small enough for the water to push through ... a plunger will have little effect in forcing this down the drain.
This may or may not work.
Your best approach at this point, now that it will drain is to use a power flusher (you may be able to rent one)the hose is sized for the drainage pipe your working with, this works by spraying high pressure water usually min 1500 psi through the hose which has a variety of different heads attached to end. Id suggest using the head that has 3 holes spraying backward as it will help u by pushing itself through the pipe.
Make sure the hose is a good 3 feet in the pipe and u have a firm grip on it where it enters the clean out turn it on and run it slowly down back and start over till it is good and clear. - Derek Plumber
Question: how to move a toilet across the room - drain vent pipe distance trouble
I am trying to move a toilet 8 feet across a room, meaning that my venting pipe will be farther away than 5 feet. If I use the same soil stack, sloping the drain pipe 2 inches down over the 8 feet, do I need to add another vent stack pipe closer to the toilet to allow for air to escape, or can I allow the toilet to vent off of the existing vent stack? If I need to tap another vent stack into the line, any recommendations on how that needs to work?
Steve, if the toilet waste line is 4" or more ID, one of the sketches above, as I read it, says you can go up to 10 feet away from the soil stack. Make sure you have proper slope as well.
Can I have 3 toilets on 3 different floors connected to the same vertical 3 inch soil pipe without separate vent pipes also added? Other wet vented fixtures are connected upstream from the toilet on the 2nd floor, which is the highest floor. - Larry Gatti
Larry, yes; you will need to review DWV layout schematics in the model codes or training manual.
Question: definitions of discharge stack, waste stack, vent pipe
what is differentiate between discharge stack,waste stack and vent pipe. - Yana
I take those terms to all refer to the vent pipe
Question: can water in the basement come from a leaky vent stack drain line?
When I have a heavy rain I have a puddle in the basement next to the bathroom drain pipes. This only happens during a heavy rain storm. Could I have a leak around the bathroom vent pipe? - Ray
Reply: yes but ... check these two other wet basement diagnosis clues
Ray, I have seen a few cases in which leaky vent stack flashing at the roof allowed water to run down the outside of a vertical plumbing vent stack pipe that in turn was enclosed in a chase-way that ran from roof to basement - water might indeed then show up in the basement.
But there are at least two other things to check:
At BASEMENT LEAKS, INSPECT FOR we provide a series of inspection points useful for sure diagnosis of the cause of wet basement floors.
Question: how much clearance between plumbing vent discharge opening and top of brick chimney?
How much height clearance do I need between my plumbing vent discharge opening and the top of my brick chimney? Our vent pipe is located about 15 inches from the chimney. Chimney and vent are near the ridge (peak) of the roof. - Tim L.
Reply: Two feet or 24" is a code interpretation for distance between plumbing vent stack rooftop termination and the top of a chimney that is less than 3 ft. away.
Tim L - thank you for your question. I've reviewed and edited our section above on plumbing vent clearances to give code citations and details. I don't find chimneys explicitly named in plumbing vent sections of the model codes, but the distance to the "Nearest window, door, opening, air intake, or ventilation shaft" distance to plumbing vent needs to be 10 ft. horizontally OR the vent should terminate at least 24" (two feet) above the opening. I take this to include chimneys.
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