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Thread: DWV layout: Will this work?

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    Luv2Q is offline New Member
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    DWV layout: Will this work?

    First, having just discovered this forum, I'll say thanks in advance to those who maintain and contribute to it. With most forums, I think it's almost expected that a newby (a) lurk awhile to see "how things are done" and then (b) be able to contribute answers along with asking questions. In other words, be a giver as much as a taker. So .. I guess I feel a little guilty coming in here with only questions and not much ability to contribute. I'm a little handy, I guess - having built some barns and shops - so maybe I can give back a little down the road.

    With all that said, here's what I'm doing: Building a standalone "mother-in-law suite" (guest house, daughter's house while in school, whatever .. though, hopefully, not a mother-in-law!). I'm planning on one single "wet wall" with water lines and DWV system all along that single wall: 2 sinks, a toilet, and a tub/shower. Main drain line is 4" PVC, with 2" PVC laterals that reduce down & tie into tub/shower and sinks. 4" closet flange. Here's the layout (if I can get an image uploaded):



    So - not having much experience with plumbing - I'm wondering what I'm missing. Will this work.

    Any & all replies appreciated. And thanks again for this forum. If nobody cares to reply, I'm still finding enough stuff in other places here to be worthwhile!

    Luv2Q .. BBQ, that is .. in TX

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    HayZee518 is offline Deity
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    where is your vent to the roof?

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    Luv2Q is offline New Member
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    Quote Originally Posted by HayZee518
    where is your vent to the roof?
    Good question, and thanks for catching it. Frankly, I was hoping to be able to use just the 3 small drain/vent lines shown.

    If I need a main vent, though, and since the cross will be at the lowest point before exiting to the septic tank, could I put a main vent on either side of the cross? And does it have to remain 3" or 4", or could it be reduced down to 2 or 2.5"?

    Maybe the following will give an idea of what I'm trying to say. Sorry for the incomplete URL but your system wouldn't allow me to submit otherwise. Something about not being able to post URLs until I've submitted 5 or more posts.

    [img]/images/uploads/2006-8-10_MainVentLoc_w550.jpg[/img]

    Thx
    Luv2Q

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    LazyPup is offline Deity
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    Luv,, Your design is totally incorrect. Your pipe sizes are all wrong and it would cause you no end to problems in the future.

    I would be glad to work out a layout for you but i need additional information. You stated that the program will not let you post illustrations yet. IF you have a floor plan with dimensions please email it to me and I will work out your plan, then post it for you.

    Also ,,do you know if your local code is based upon the Uniform Plumbing Code or the International Residential Code?

    Email to LazyPup@yahoo.com

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    Luv2Q is offline New Member
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    LazyPup ..

    Thanks! I've taken you up on your offer & forwarded a floor plan plus a couple of other illustrations. BTW, the wall with the plumbing fixtures on the floor plan is 28' in length.

    Luv2Q

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    Since this line will be coming into the house direct from the house sewer and septic tank it must be treated as a completely separate "Main Drain".

    The first step is to determine the diameter of the main drain line. In order to do so we must first determine the total load that this drain must handle.

    In the code book we have a list of all the fixtures that would commonly be found in the home. The list then assigns a DFU (Drainage Fixture Unit) value and it defines the required size of trap for the fixture.

    In this example we have a watercloset, lavatory bowl, tub/shower & a kitchen sink. From the International Residential Code table 3201.7 we get the following values:

    Water closet (less than 1.6gal/flush) 3DFU 3" line
    Lavatory bowl 1DFU 1-1/4" trap
    Tub/shower 2DFU 1-1/2" trap
    Kitchen sink 2DFU 1-1/2" trap.
    Total DFU 8DFU

    Understanding that a drain line may never be reduced in size in the direction of flow we must then use a minimum 3" line to meet minimum for a watercloset.

    A 3" main drain or sewer with a 1/4" per foot pitch is rated for up to 42DFU so the main will be a 3" line.

    Under the International Residential Code we are required to have one "Main Vent" which must run undiminished in size from the main drain up through the roof. Auxillary vents may then be reduced to 1/2 the diameter of the line they serve and may termintate through the roof, in the attic space, under limited conditions through the wall or you may use an ulimited number of AAV(air admittance valves).

    Under the Uniform Plumbing Code all vents may be reduced to 1/2 the diameter of the line they serve but the combined aggregate total of cross sectional area must be equal to or greater than the cross sectional area of the main drain. The UPC requires all vents to go through the roof and it only permits a maximum of one AAV per structure with the expressed permission of the local AHJ. (In this example we will only have two vents so one of them must be 3" to get the required cross sectional area)

    Begin at the closet flange and run a 3" main line straight out of the buiding to the sewer connection. For slab constrution you will need a "Main cleanout" at the junction of the building Main Drain & Building Sewer approximate 3' outside the foundation wall.

    Code prohibits installing a Sanitary Tee in a horizontal line so on the 3" line at the wall you will install a 3" double sanitary Wye with a street 1/8th bend in each side opening to give you a 90 deg angle. On the left side you will install a second 3" sanitary Wye with the side opening point up and run a 3" vent vertical up through the roof. On the end of the second wye install a 3"x1-1/2" reducer bushing and run an 1-1/2" line horizontal to the lavatory position and turn it up to the lavatory. Under the IRC if the combined length of sections A & B do not exceed 6' there is no additional venting required for the lavatory.

    From the double Wye position GOING RIGHT install a 3" x 2" reducer bushing then a 2" dia. 1/8th bend to turn the pipe at right angles to the 3" main. Continue the 2" to the tub location. Install an 2"x 1-1/2" x 1-1/2" wye (Or a 2" wye with 2" x 1-1/2" reducers on the side & upstram ends) From the side opening install a 1-1/2"--1/8 bend and a short section of 1-1/2" to the tub trap.

    From the end of the Wye continue the 1-1/2" left until you reach a point just on the right hand side of the window by the kitchen sink. Install a Wye & 1/8th bend and run an 1-1/2" line vertical for a vent. Then continue the 1-1/2" toward the right until you reach the sink location and turn up to the sink.

    As a side note: Your floor plan shows a water heater and furnace in the utility space between the bathroom and kitchen. The door to that utility space is opening into a bedroom. The Plumbing code prohibits installing a Gas Water heater in a Bathroom, Bedroom or a utility room which opens into a Bathroom or Bedroom. An electric water heater would be ok. You should also check your local mechanical code to see if there are similar restrictions on a gas furnace.
    Attached Thumbnails Attached Thumbnails DWV layout:  Will this work?-floor-plan.jpg   DWV layout:  Will this work?-isometric.jpg  
    Last edited by LazyPup; 08-14-2006 at 06:24 AM.

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    Luv2Q is offline New Member
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    My gosh! I can't believe how much this helps. Not only is it done right, but I'm sure the materials cost will be way less than the contraption I was about to put together. Can't wait to get 'er done! Want me to post some pix?

    LazyPup, words just can't describe how much I appreciate what you've shown me. But two I'll try right now: Thank You!

    Luv2Q
    (Love the isometric .. tells the whole story!)


    Edit: By the way, the HWH & furnace will be electric. Thx for the heads-up on this, though.

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