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Schematic of a direct vented plumbing fixture (C) Carson Dunlop AssociatesPlumbing Vent Distances & Routing Codes

Plumbing vent distances, routing, clearances:

This article gives recommended or allowable distances from plumbing vent to fixtures, and distances from plumbing vent to building features like chimneys, windows, roofs, walls.

This article series includes definitions of plumbing vent terms, types of plumbing vents, plumbing vent size requirements, plumbing vent clearance distances to building roof, vertical walls, nearby windows, or plumbing vent distance to chimneys.

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.

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Plumbing Vent System Distances & Routing

Plumbing vent terminology sketch (C) Carson Dunlop Associates The basic plumbing vent terms are shown in the sketch.

In these notes, the plumbing stack vents and other sketches included below are provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

[Click to enlarge any image]

Article Contents

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.

The usual slope on the fixture drain piping is 1/4" of slope per 12" (foot) of horizontal distance or "run" of piping.

Distances: How far can the plumbing vent piping be located from a plumbing fixture?

Schematic sketch of distance allowed between a plumging fixture and vent piping (C) Carson Dunlop Associates

As we discuss at PLUMBING DRAIN NOISE DIAGNOSIS, 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 Associates' 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.

Tables of Plumbing Drain Pipe & Vent Pipe Sizes (1) and Critical Distances to Plumbing Fixtures (2)

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.]

Table 1. Plumbing Drain Pipe Sizes
Drain Pipe Diameter Vertical Drain Pipe, Maximum Number of Fixtures Horizontal Drain, Maximum Number of Fixtures
1-1/4" dia 1 1
1-1/2" dia 2 1 (or 2 sinks)
2" diam 16 8
2-1/2" dia 32 14
3" diam 48 35
4" diam 256 216
 

Notes to Table 1 above

Note: you can see from this table that at common home drain pipe sizes, if your pipe is 2" or larger you're unlikely to run into drain capacity trouble.

Table 2. Vent Pipe Distances
Drain Pipe Size Vent Pipe Size[1] Distance [2]
1-1/4" diam 1-1/4" diam 2-1/2 feet
1-1/2" diam 1-1/4" diam 3-1/2 feet
2" diam 1-1/2" diam 5 feet
3" diam 2" diam 6 feet
4" diam 3" diam 10 feet

Notes to Table 2 above

[1] Minimum diameter of the vent pipe

[2] Critical distance between the plumbing fixture and the vent pipe. You can see that for vent pipe diameters under 4" you need to be vigilant about not locating a plumbing fixture too far from its vent pipe/stack

Plumbing Vent Routing Specifications

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.

Special routing and connections are required for proper venting of plumbing fixtures such as kitchen island or peninsula sinks or dishwashers - plumbing fixtures that are located where a direct vertical vent stack connection is not possible.

See ISLAND SINK PLUMBING VENTS for details.

Table of Plumbing Vent Clearance Distances to Building Features

The table below gives required clearance distances to various building features and cites pertinent model plumbing codes.

Building Feature

Required Distance from Plumbing Vent Termination to Building Feature

Comments
Roof Surface, distance to Plumbing Vent 6 inches above nearest roof surface "nearest" accommodates sloped roof - i.e. measure from the "up-roof" side
Nearest vertical surface, distance to plumbing vent 12 inches from nearest vertical surface such as the side wall of an upper story on the building

Nearest window, door, opening, air intake, or ventilation shaft: distance to plumbing vent.

 

 10 ft (120 inches) from nearest window, measured horizontally

- OR 2 ft. (24 inches) above nearest window [or other opening listed at left], measured vertically		 We interpret this rule to apply to the required separation distances between a plumbing vent and nearest chimney on the building - Ed.

Notes to the table above

Distances are measured horizontally unless we indicate otherwise

Plumbing Code Citations for Plumbing Vent or Vent Stack Clearance Distances

Quoting the IRC model plumbing code

12.4 VENT TERMINALS

12.4.1 Extension Above Roofs

Vent pipes shall terminate not less than 6 inches above the roof, measured from the highest point where the vent intersects the roof. EXCEPTION: Where a roof is used for any purpose other than weather protection, vents shall extend at least 7 feet above the roof and shall be properly supported.

12.4.4 Location of Vent Terminal

a. Vent terminals shall not be located where vapors can enter the building.

b. No vent terminal shall be located directly beneath any door, window, or other ventilating opening of a building or of another building,

nor shall any such vent terminal be within 10 feet horizontally of such opening unless it is at least 2 feet above the top of such opening.

c. Where a vent terminal is within 10 feet horizontally and less than 2 feet above a ventilation opening described in Section 12.4.4b

and the line-of-sight from the vent terminal to the ventilation opening is interrupted by the continuous ridge of a roof, the ridge shall be at least 2 feet above the top of the opening. Otherwise, the vent terminal shall comply with Section 12.4.4b.

d. Where a vent terminal is within 10 feet horizontally and less than 2 feet above a ventilation opening described in Section 12.4.4b and the line of sight from the vent terminal to such ventilation opening is interrupted by a solid wall or solid barrier, the top of the wall or barrier shall be at least 2 feet above the top of the ventilation opening

and the shortest travel distance around the wall or barrier from the vent terminal to the nearest edge of the ventilation opening shall be at least 10 feet. Otherwise, the vent terminal shall comply with Section 12.4.4b.

Plumbing Vent Codes

Code Citations for Plumbing Vent Terminals at the Rooftop or Through Walls

904.1 Roof extension.

 All open vent pipes that extend through a roof shall be terminated at least [NUMBER - typically 6 ] inches (mm) above the roof, except that where a roof is to be used for any purpose other than weather protection, the vent extensions shall be run at least 7 feet (2134 mm) above the roof.

904.2 Frost closure.

 Where the 97.5-percent value for outside design temperature is 0ºF (-18ºC) or less, every vent extension through a roof or wall shall be a minimum of 3 inches (76 mm) in diameter. Any increase in the size of the vent shall be made inside the structure a minimum of 1 foot (305 mm) below the roof or inside the wall. 

904.3 Flashings.

 The juncture of each vent pipe with the roof line shall be made water tight by an approved flashing.

904.4 Prohibited use.

Vent terminals shall not be used as a flag pole or to support flag poles, television aerials or similar items, except when the piping has been anchored in an approved manner. 

904.5 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 at least 2 feet (610 mm) above the top of such opening.

904.6 Extension through the wall.

 Vent terminals extending through the wall shall terminate a minimum of 10 feet (3048 mm) from the lot line and 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.

904.7 Extension outside a structure.

 In climates where the 97.5-percent value for outside design temperature is less than 0ºF (-18ºC), vent pipes installed on the exterior of the structure shall be protected against freezing by insulation, heat or both. 

Plumbing Codes, Citations, Fulltext Codes, & Plumbing Code References

Watch out: while the 2015 IPC is the most-recent version of the International Plumbing Code, the 2018 IPC is under development. To understand which generation of the model building code or plumbing code applies to your specific project you will need to check with your local building official. For example many jurisdictions are on the 2012 IPC or still older versions.

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2024-01-17 by Ken

When trying to vent together at the same level, can you use a Ty on its back?

On 2024-01-17 by InspectApedia Publisher

@Ken,

If it's a dry vent I don't think there's any problem.

On 2022-12-02 by Tc

Is it true that in 2009 a toilet gas pipe did not have to be routed through the roof

On 2022-12-03 by InspectApedia (Editor) - does a toilet gas pipe have to be routed through the roof

@Tc,

No not in any country that has plumbing codes, though let me be more clear:

A building plumbing vent system should extend above the level of the surface of the roof but does not in every instance have to pass literally *through* the roof - that is, in some plumbing installations a vent is routed out through a building wall, up the building exterior, and then above the roof.

Also

Some individual building fixtures might, depending on local plumbing code enforcement, be permitted to use an air admittance valve (AAV) or "studor vent" where connection to the building's main plumbing drain waste vent (DWV) piping does not permit easy connection to the vent pipe.

On 2022-10-24 by David Nelson

Can a AC input line be right up against the underside of the roofing sheathing ?

On 2022-10-26 by InspectApedia (Editor) - Can a AC input line be right up against the underside of the roofing sheathing?

@David Nelson,

No that's a mistake.

The problem is that during reroofing someone's going to drive a shingle nail through shingles and decking plywood or OSB, and there's a good chance that it will puncture the refrigeration tubing.

It would be smarter to keep refrigeration piping several inches away from the underside of the roof deck.

If refrigeration piping or tubing absolutely has to run uptight against the under side of the roof deck it should be protected throughout that run by a steel protection plate.

On 2022-09-09 by Brett

Is it possible to vent a 96+ furnace over to a common 5" double wall through the roof vent?


On 2022-09-09 by InspectApedia-911 (mod) - check BTU input rate for accepatable chimney and flue size

@Brett,

You have to look at the total BTU input rate to the chimney and fluent connector. That is you look at the btu rate of all the devices being connected. Chances are with the flu that small you're going to be overloading it and it'll be unsafe

On 2022-07-08 by jeff

can I run a 3 inch DWV pipe up (vertical) through a 6 inch stem wall for a garage toilet

On 2022-07-08 by InspectApedia-911 (mod)

@jeff,

Perhaps I am missing some part of an underlying question here but in general I don't see an issue in running 3-in vent pipe vertically inside of a 6 inch thick wall.

On 2022-07-08 by jeff

Its a cement floor so i have to make all the drain connections before i pour the cement .when i pipe in the toilet drain I wanted to run the vent from the toilet up through the stem wall and footing

On 2022-07-08 y InspectApedia-911 (mod) - It's generally okay to run PVC pipe inside of a concrete floor

@jeff,

It's generally okay to run PVC pipe inside of a concrete floor or wall in the concrete will not react with or damage the pvc. However I'm a little nervous about running unprotected PVC up through the footing.

The PVC won't react with the concrete but concrete shrinkage or footing movement could end up causing a leak in the pipe.

Good practice therefore is to provide some padding around the PVC where it runs through the concrete footing. There are foam products sold for this purpose but some plumbers simply wrap the PVC in cardboard before pouring the footing.

On 2022-07-03 by Nate

Can u use a double wye upside downs vertical to connect two other vents.

On 2022-07-04 by InspectApedia-911 (mod) - you can use wyes to connect plumbing vents but...

@Nate,

Yes but no.

Yes you can use wyes to connect plumbing vents, but if you combine two vents of a given diameter, say both = 2" into a 3-way 2" wye, you are cutting the vent capacity in half and may have drain problems or even trap siphonage that can be dangerous (methane gas explosions in buildings).

So don't reduce the combined venting diameter below the sum of the two vents being joined.

On 2022-06-13 by Rick

Can a 3” drain pipe for a toilet be 30’ long? The drain pipe will have 1/4” drop per foot and a 2” vent pipe 1’ from the toilet.

On 2022-06-14 by InspectApedia-911 (mod) - Can a 3” drain pipe for a toilet be 30’ long?

@Rick,

My gut reaction is there's a clog risk from a long small-diameter drain but in fact PROVIDED the distance you're discussing in the actual horizontal 3-inch diameter drain run length to a sewer or septic system, there is no horizontal length limitation in the model plumbing codes.

The plumbing codes do give a maximum vertical distance of 212 ft. for 3-inch drain piping.

You do want to calculate the total number of DFUs (Drain Fixture Units) to be sure you're within the limits for 3-inch drain piping of

- 20 DFUs for any horizontal fixture branch
and
- 48 DFUs for any vertical plumbing stack or drain

(It's unlikely you're going to violate that limit in a residential installation).

Check with your local plumbing code compliance inspector. In most jurisdictions a 3-inch waste line connecting a toilet is still permitted, though as I'll elaborate: not optimal.

Best practice (and in new construction) you'd use a 4-inch pipe (or larger) for the main building drain and you'd run 4-inch drain piping from the toilet to the main drain. Using a 3-inch drain at a toilet was common in older plumbing systems but isn't something we'd recommend in new construction

In my experience with older homes where 3-inch drain pipes were common, those lines were more-prone to clogging.

Watch out: where you could run into a problem is a long in-building horizontal run of any drain that, if inadequately-vented, carries so much water that it creates enough vacuum back towards the fixture that it siphons the water out of the fixture sink drain. In the case of a toilet, that's less likely.



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