# Drains and Vents in a Unique Concept House (long post)



## Robert Ellenberg (Jun 17, 2010)

I have built and designed houses for over 30 years and have always studied the codes—except plumbing.  I have relied on the plumber who was doing the work to properly size and run the DWV system and I had very limited knowledge of how or why it needed to be a certain way.

For the past 3-4 years I have been working part time designing a unique concept “kit” house.  The plans (intent) is to have the structure pre assembled as weather tight modules and include all materials needed to complete the house, pre sell them and ship them to different parts of the country.  That means that in many jurisdictions they will need to exceed the IRC standards.  I am working on the designs for the plumbing DWV systems so over the past few months I have been studying in an effort to gain the knowledge needed to design them to meet the strictest codes.

I have come up with an unusual way to tie the vents together and I believe it meets the codes, but because I can’t find anything quite like it to compare it to—I am not sure.  My question relates to how I propose to run the vents in regards to some unique features of the designs.  These are small one story homes with conditioned crawl spaces (no slabs) with one or two baths.  To increase the usable interior volume, most of the interior partitions will be unique prebuilt panels only 2.5” thick—not enough for drains or vents in most of the walls.  We will thicken them or make a chase where necessary to run vents up.  However, they cannot be tied together above the ceiling line for a single exit through the roof because the flat ceiling-roof structure will be filled solid with foam (no attic or space of any kind) and we don’t want a roof peppered with numerous vents.

I want to try and explain how we intend to do it and I would like to know if it sounds as if it meets all of the codes relating to drains and vents. My question only relates to routing as I know you can’t comment on pipe sizing etc., without more information.

The tub and shower drains and traps will be in the crawl space.  I want to take the sinks and laundry stand pipe through their traps in the cabinets and drop the drains straight through the floor (is this permitted as long as the trap is close enough to the bottom of the sink drain?).  Under the house, take all of the properly sloping drains under the floor from the individual fixtures and tie them into a main horizontal drain pipe that is sized correctly and has the toilets tied in as well.    The high end of that main drain would be a 3” pipe with a sweep and clean out plug and the sweep turns upward taking a 3” vent up a chase and through the roof.  We will then have an individual vent pipe connected to each drain line within the crawl space, connected to the top centerline within the prescribed distance from the fixture trap, immediately going into a 90 bend and sloping upward at ¼” /foot (under the floor in the crawl space), all converging on the chase where the 3” vent from the end of the drain goes up through the roof.  Turn the vent pipes up inside the chase (90 turn upward) and take the individual vents up to a height at least 6” above the flood rim of the fixture they serve and tie them into the 3” vent.  Here is another way to explain it:  you normally take individual vents up to the attic, make a 90 and take them on an upward slope of 1/4"/foot to where they tie in to the large vent pipe and exit the roof.  I am proposing to do it in a similar way except run them under the floor instead of in the attic over to the chase and then get them above the fixture rim flood height before tying them into the 3" vent that exits through the roof.

If I haven’t given enough information for some of you master plumbers/inspectors to answer, post questions and I will try to respond.  And remember, I am not a plumber or plumbing inspector but a designer-builder trying to get it right before it is built and you come out to look at it!


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## north star (Jun 17, 2010)

** * **

*Robert,*

*If possible, can you post some pics. / drawings / rough sketches on here for*

*a better understanding of what you are proposing?     We're all about pics.*

*ya know...  * 

*Also, have you contacted the Plumbing & Drainage Institute for their input.*

*Yes, it's going to cost you some money for their analysis.*

** * **


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## georgia plans exam (Jun 17, 2010)

Yes, a diagram would help. Keep in mind I.R.C. (2006) Section R3105.2 that requires the vent pipe connection to the fixture drain, except for water closets, to be above the weir of the trap.

GPE


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## Robert Ellenberg (Jun 17, 2010)

Thanks for the responses so far.  I will try to make a sketch tonight that can be understood.

North Star--I looked at the P&DI site but I am not looking to get approval on something new, I want to design something that meets the codes as they are written and I think this does.

Georgia--Yes.  Note I stated, "We will then have an individual vent pipe connected to each drain line within the crawl space, connected to the top centerline within the prescribed distance from the fixture trap, immediately going into a 90 bend and sloping upward at ¼” /foot (under the floor in the crawl space)".  This would definitely be above the trap weir.


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## Robert Ellenberg (Jun 17, 2010)

I am trying the attachment (haven't done it before).  If it is here, I'll post the explanation.


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## Robert Ellenberg (Jun 17, 2010)

The sketch is crude but perhaps you can understand it.  Look at the one on the right first.  The red lines represent the drains and the ornage lines the vents.  The main drain line would start at the highest point under the floor just under the half wall where all of the orange lines are converging. It turns up in a sweep as a vent going up through the roof.  from there it slopes down toward the front of the house and the individual fixture drains are tied into it. The orange lines represent vent lines attached to the top centerline of the drain lines.

If you look at the left drawing, it shows the drains slope down and the vents slope up with the vents all going to where the vent goes through the roof.  They would go up inside the chase next to the vent to a point higher than the rim of the sink and then tie into the main vent.


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## globe trekker (Jun 18, 2010)

Robert,

Thanks for posting the drawing!

Your design looks to be compliant, from what I can tell.   Keep in mind, no flat vents,
...the correct fittings to be installed  [  i.e. - long sweeps, sanitary tees  vs.  Y's, etc., ]
and as a former plumber, please do not install all of the fittings together so close so
someone cannot work on them in the future or inspect them.   Please leave some
room for accessing the individual fittings.


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## skipharper (Jun 18, 2010)

You can view the 2006 Virginia Residential Code online at the link provided below and look for appendix N which has illustrations of various venting methods. These are the same that are in The International Residential Code. This would apply where dwellings are sent to States that use the IRC. Not sure what is in The Uniform Plumbing Code (UPC) but should be similiar.

http://www2.iccsafe.org/states/Virginia/Residential/Res-Frameset.html


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## JMORRISON (Jun 18, 2010)

You can wet vent the whole group.


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## EPrice (Jun 18, 2010)

From IRC Chapter 2, definitions:



> *Horizontal Pipe.*  Any pipe or fitting that makes an angle of less than 45 degrees (0.79 rad) with the horizontal.


If those sloped sections of vent are run at an angle of less than 45 degrees to the horizontal, they are horizontal dry vent sections.

Also from the IRC:



> *P3104.4 Vertical rise of vent.* Every dry vent shall rise vertically to a minimum of 6 inches (152 mm) above the flood level rim of the highest trap or trapped fixture being vented.


It seems likely to me that you will be in violation of this section.  You may also be in violation of Section P3104.5.

JMORRISON's suggestion seems to be the best way to go.


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## Bootleg (Jun 18, 2010)

Quote: Robert said...

(I want to take the sinks and laundry stand pipe through their traps in the cabinets and drop the drains straight through the floor (is this permitted as long as the trap is close enough to the bottom of the sink drain?).

Robert,

Where is the laundry stand pipe with p-trap on you drawing?


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## Robert Ellenberg (Jun 18, 2010)

JMorrison--I have read other references that dry venting is preferable if possible so that is what I was attempting.  Is that correct?

EPrice--Yes, they would be sloped at less than a 45, dry (sloped back min. 1/4"/FT for condensation) and they would turn up inside the chase, going vertical and then connect into the 3" vent at a place 6"+ above the rim of the highest sink, with the 3" continuing up through the roof .

Bootleg--I did not show it simply because my rough sketch already looked cluttered. However, the question was simply could the Ptrap be at the bottom of the stand pipe just under the floor (basically in the same plane as tub and shower P traps).  I think the IRC allows it to be 42" below the top of the stand pipe but I didn't know if the UPC or other codes permitted the P trap to be done this way.


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## Bootleg (Jun 18, 2010)

Quote: Robert said...

(the question was simply could the Ptrap be at the bottom of the stand pipe just under the floor (basically in the same plane as tub and shower P traps). I think the IRC allows it to be 42" below the top of the stand pipe but I didn't know if the UPC or other codes permitted the P trap to be done this way.)

2006 UPC  804.1

No trap for clothes washer below the floor.


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## JMORRISON (Jun 22, 2010)

Here is good interp from Dave Cantrell.  This is in parts due to file size.

 SEATTLE / KING COUNTY PUBLIC HEALTH

Community Environmental Health

Plumbing / Gas Piping Inspections

DECISIONS / INTERPRETATIONS

of the Chief Plumbing Inspector

Date: August 16, 2007 Decision No. 07-004

REVISED

Subject: Bathroom (Horizontal) Wet Venting

Code / Section: 2006 UPC Section 908.4

Decision. All bathroom wet venting installations shall conform to Section 908.4 and the guidelines contained in the attached document entitled “2006 UPC Section 908.4 – Bathroom Wet Venting Guidelines.”

Background. Section 908.4 contains provisions for horizontal wet venting of residential use bathrooms. This is based on the same horizontal wet venting provisions of Section 909 of the 2006 International Plumbing Code (IPC). However, some of the information found in the IPC was not included in the UPC. The intent of the attached document is to provide additional information necessary to meet the minimum installation requirements of Section 908.4.

Attachment: 2006 UPC Section 980.4 – Bathroom Wet Venting Guidelines


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## JMORRISON (Jun 22, 2010)

Guidelines

2006 UPC Section 908.4 - Bathroom Wet Venting Guidelines

1. Section 908.4.1

Any combination of fixtures within one (1) or two (2) bathrooms located on the same floor level and serving dwelling units or sleeping units shall be permitted to be vented by a wet vent.

The bathrooms being wet vented must be located on the same floor level The intent is that the two bathrooms would be relatively close to one another, such as back-to-back or side-by-side.

The wet vent may serve bathrooms that are located within dwelling units and sleeping units in Group R and Group I-1 occupancies as defined in the Building Code. This includes, but is not limited to single family dwellings, duplexes, townhouses, apartment houses, boarding houses, hotels, motels, dormitories, residential board and care facilities, assisted living facilities, halfway houses, group homes, social rehabilitation facilities, and convalescent facilities. Community bathrooms that serve multiple dwelling or sleeping units, or public and employee restrooms within these occupancies shall not be served by a horizontal wet vent system.

A “dwelling unit” is defined in the Building Code as “a single unit providing complete, independent living facilities for one or more persons, including permanent provisions for living, sleeping, eating, cooking and sanitation.”

A “sleeping unit” is defined in the Building Code as “a room or space in which people sleep, which can also include permanent provisions for living, eating, and either sanitation or kitchen facilities but not both.”

2. Section 908.4.1 (cont’d)

The wet vent shall be considered the vent for the fixtures and shall extend from the connection of the dry vent along the direction of the flow in the drain pipe to the most downstream fixture drain connection to the horizontal branch drain.

The vent (dry vent) serving the horizontal wet vent shall serve the uppermost fixture. Section 908.4.2 provides guidelines for the installation of the dry vent. (See Item 4)

3. Section 908.4.1 (cont’d)

Only the fixtures within the bathroom(s) shall connect to the wet-vented horizontal branch drain. Any additional fixtures shall discharge downstream of the wet vent system and be conventionally vented.

If the fixture is not part of the bathroom(s) being wet vented, it must connect downstream of the wet vent. The intent is that only those fixtures that are ‘bathroom’ type fixtures are allowed to be served by the wet vent. ‘Bathroom’ type fixtures are water closets, lavatories, bathtubs, showers, combination bathtub/showers, bidets and floor drains. A


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## JMORRISON (Jun 22, 2010)

laundry washer or laundry sink that is located within a bathroom shall not be served by the wet vent and must connect downstream of the wet vent.

4. Section 908.4.2 Vent Connection.

The dry vent connection to the wet vent shall be an individual vent or common vent for the lavatory, bidet, shower or bathtub.

The dry vent shall be located at the most upstream fixture served by the wet vent. Where the bathroom vent serves one or more water closets the dry vent must be a minimum of 2-inches in diameter. The dry vent may also serve as a drain for one or more fixtures, such as lavatories. Where the dry vent does not serve as a drain, the connection of the dry vent to the horizontal wet vent shall be in accordance with Sections 905.2 and 905.3.

5. Section 908.4.3 Size.

The wet vent shall be sized based on the fixture unit discharge into the wet vent. The wet vent shall be a minimum size of 2 inches for 4 dfu or less, and 3 inches for more than 4 dfu.

The sizing of the individual sections of the wet vent is based on the drainage fixture units discharging into that specific section of piping. The minimum size of the wet vent is 2 inches in diameter, which may serve up to 4 drainage fixture units. Only that portion of the wet vent that exceeds 4 drainage fixture units would need to be increased to a minimum 3 inches in diameter.

Additional notes:

•

Since the wet vent serves as the vent for the fixture traps, the installation of the trap and trap arm, including the minimum and maximum distance of a trap to the wet vent shall be in accordance with Chapter 10.

•

The horizontal wet vent shall be installed at a minimum ¼-inch per foot slope.


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## JMORRISON (Jun 22, 2010)

here is picture

View attachment 143


View attachment 143


/monthly_2010_06/Bathroom_Horizontal_Wet_Venting.jpg.52660c8f1c1dfd1c7ea68abdea5b22b7.jpg


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## Robert Ellenberg (Jun 22, 2010)

JMorrison--Thank you so very much!  Much of what is published assumes you have a basic knowledge and is difficult to understand--this was of tremendous help.  I have a question concerning the connection of other fixtures such as a washer or kitchen sink because I have a laundry right behind the bath.  It says the laundry has to have a separate vent and can only connect downstream of the wet vented bath group.  Can the laundry vent go back and tie into the dry vent for the bath group as long as it is above the rim on the lavatory, that first fixture that is in the vertical section of the wet vent?  In other words, the laundry vent would be the highest connnection on the vertical dry vent and the first drain connection beyond the section of drain pipe that is classified as wet vent.


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