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Thread: Three questions about adding a basement bathroom

  1. #1

    Default Three questions about adding a basement bathroom

    Hello all,

    I've referred to posts here a lot over the last few months. Now it is time to tackle a big project (for me at least) and I want to make sure I do it right.

    I would like to add a bathroom with shower in my basement. The floor is a 4" slab.

    There is an existing drain (3" interior diameter/4" exterior - made of metal - would this be a steel pipe? It is original to the home - 1940's) that comes out of the floor about 1" before it is capped. Previously this drain continued up to the 1st floor where it met the kitchen sink and then vented out of the house. The kitchen sink no longer exists in that location so the drain was cut just above the basement floor and removed.

    I have three questions...

    1) Can I tie into this existing drain for a shower, sink, and toilet?

    2) What order must I/should I go in? ie shower -> toilet -> sink -> existing drain?

    3) What do I need in regards to ventilation? This bathroom is smack in the middle of the basement - the nearest exterior wall is about 15' away. Venting through the roof is not feasible due to the layout of the rooms above. I have no problem running a vent through the ceiling joists and out the side of the house - is that allowed?

    Any help is greatly appreciated. I have limited plumbing experience but am looking to learn. I am very competent in most other household remodeling areas. I have broken up/replaced sections of concrete slab before so that part of the project at least I know I have a grasp on.

    Thanks in advance for all the wonderful advice I know I am going to receive!

  2. #2
    Plumbing Designer FloridaOrange's Avatar
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    1. Yes, depending on the venting of the existing layout.
    2. All depends on the existing venting. If all vfixtures are vented separately then it doesn't matter. On a wet vent typically the water closet is not before the shower/tub to eliminate the toilet flushing sucking the other traps dry.
    3. Side venting can be done as long is there isn't an operable window above and according to my code you need to be 10 feet above grade.

    Your jurisdiction will help narrow the answers done, my answers are mostly based on Florida and International Plumbing Codes.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  3. #3
    Moderator & Master Plumber hj's Avatar
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    Default Dwv

    The order of the fixtures is immaterial as long as you install proper venting for them. Outside venting is usually NOT permitted in areas which have freezing winters, but we do not know where you live. Call your building department, or find out when you apply for the permit to do the work.

  4. #4

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    It sounds like venting is very important

    I live in Maryland and we do have freezing winters. I will check the local code to see what it says about this. Thanks!

  5. #5
    Forum Admin, Expert Plumber Terry's Avatar
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    Venting is half of plumbing.
    Without vents, traps would siphon dry, and you would have open pipes between the septic tank and you bedroom night stand.
    Now that's a sweet thought.

    Helpful Plumbing Hints for Residential Construction by Bert Polk Plumbing Inspector Lincoln County
    Last edited by Terry; 05-24-2010 at 03:30 PM.

  6. #6
    In the Trades Gary Swart's Avatar
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    You are embarking on a project that has many pitfalls. In my not-so-humble opinion, you would be wise to hire a plumber to do this project. It will be very costly if you get the job finished only to find you screwed up big time and have to tear everything out and redo it.

  7. #7
    Master Plumber-Gas Fitter shacko's Avatar
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    Default Basement Bathroom

    I don't know of anywhere in Maryland that allows a vent thru the walls, sorry.

  8. #8
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by shacko View Post
    I don't know of anywhere in Maryland that allows a vent thru the walls, sorry.
    Do you guys allow air admittance valves (aka Cheater Vent) in your code?

    They were basically invented for this very purpose.... putting a bathroom in a finished basement. But again I don't know if your code allows them.

  9. #9

    Default

    Poking around my basement this afternoon I found an unused vent. It looks like it was cut out of the current plumbing system by the plumber we hired to do the work for our kitchen. It was hidden up between the joists against a far wall in the basement which is why I did not see it before. I checked and it does indeed run all the way to the roof.

    This vent is still about 15' from where my bathroom would be. Can I use this? The part I can reach is plastic and about 2" exterior diameter. I can see farther up that it is becomes metal pipe although I can't easily measure the diameter (it look larger than 2" exterior).

  10. #10

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    Doherty -

    The drain for our washer uses an air admittance valve. That was recently installed by a licensed plumber and passed inspection. I assumed something like that could not be used for a bathroom... mainly because it seemed like such an easy solution I thought that there must be a catch.

  11. #11
    Retired Defense Industry Engineer jadnashua's Avatar
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    As long as you can maintain at least a 1/4" per foot slope on any horizontal sections, you can use that vent line. The reason vents still need slope is to account for condensation or precipitation that might otherwise accumulate...you don't want that to block your vent - it must drain.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  12. #12
    DIY Senior Member seaofnames's Avatar
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    You cant go around putting AAV's on everything you want to add to your system. For code here in BC you CAN use AAV's, but there must be a regular vent somewhere in the system. I cant remember if it depends on number of fixtures, but if you can vent normally, I'd stick with that first. If all else fails, then use an AAV... if its allowed for what you are doing.

  13. #13
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by seaofnames View Post
    You cant go around putting AAV's on everything you want to add to your system. For code here in BC you CAN use AAV's, but there must be a regular vent somewhere in the system. I cant remember if it depends on number of fixtures, but if you can vent normally, I'd stick with that first. If all else fails, then use an AAV... if its allowed for what you are doing.

    In BC you are allowed to use AAVs to vent island counters, fixtures that may be affected by frost closure, fixtures under renovation, or installations where connection to a vent may not be practicable. Like in a bathroom in the basement of a finished house.

    You must make the AAV accessible and it needs to be in a space where it can suck in air. Usually you put it up high on the wall and put a return air grill over it to let it suck in air outta the room.

    And yes you're right there must be atleast one vent going to the outdoors in the system somewhere.

  14. #14
    Moderator & Master Plumber hj's Avatar
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    Default Aav

    One proper vent through the roof is required because the AAV cannot handle Positive pressure. An AAV can make the job easier to install, but CAN create its own problems when certain conditions, such as partial stoppage of the main line occur. With an AAV you cannot be certain, without further testing, whether lack of drainage is a symptom of other problems elsewhere, or because that fixure's drain line is plugged.

  15. #15
    In the Trades Gary Swart's Avatar
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    Dryer vents ( and water heater vents) are NOT part if a sewer vent. It might be more accurate to call dryer and water heater "vents" exhausts, but I don't expect we'll change tradition and do that.

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