Sewer line proximity to foundation

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by Leah F., Mar 26, 2014.

  1. Leah F.

    Leah F. New Member

    Messages:
    6
    Location:
    Orange County, California
    Hello,
    I would like to create an addition to my house. It will be a raised foundation with a standard crawl space. I will also be replacing the sewer line that runs in that area. Can the addition stem wall and footings be run directly atop of the new sewer line or is it better to have the sewer line run outside the foot print of the house?
    Thank you.
    Leah

    2014_03_26_09_37_13.jpg
    Last edited: Mar 26, 2014
  2. Terry

    Terry Administrator Staff Member

    Messages:
    15,000
    Location:
    Bothell, Washington
    Footings for a home need to be on "un-disturbed" soil.
    Trenching near a foundation needs to be far enough away that the weight of the foundation and the home setting on the foundation doesn't cause the ground to shift.

    Speaking of ground that slides, here is our local example.

    http://www.usatoday.com/story/news/nation/2014/03/24/washington-mudslide/6823195/

    Also, unless you intend to hand dig that line, it will need to be far enough away for a back hoe to set up without hitting structure.
  3. Leah F.

    Leah F. New Member

    Messages:
    6
    Location:
    Orange County, California
    Dear Terry,

    Thank you.

    Wow. So much rain. I am sad for the people and animals. It appears that it is raining everywhere except here in California.


    If I were to leave 3 feet between the structure and the sewer line, would that leave enough undisturbed space for hand digging in the event of future failure?

    L
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,615
    Location:
    Cave Creek, Arizona
    The standard is that the trench has to be on a 45 degree angle away from the footing, which means for every 12" it is below the footing, the ditch has to be 12" away from it.
  5. Leah F.

    Leah F. New Member

    Messages:
    6
    Location:
    Orange County, California
    Thank you.
    I don't suppose anyone could spell out possible solutions to modifying my sewer line to accommodate the addition? The sewer line pops out from below the stem wall (18 inches down) right where the toilet is at the back of the house (see existing drawing above). The pipe is travelling out into the yard pretty much where I want to build the addition. Where is a good placement for the new sewer line? Would maybe 2 feet away and parallel with the addition foundation be good? Would it be better instead to change the course of the sewer line to be under the existing house and pop out from the side instead of out from the back the way it is?
  6. dj2

    dj2 Member

    Messages:
    411
    Location:
    California
    "I don't suppose anyone could spell out possible solutions to modifying my sewer line to accommodate the addition?"

    You have the answer, HJ gave it to you.

    How far is your existing line from the house on the right side?
  7. Reach4

    Reach4 Active Member

    Messages:
    2,229
    Location:
    IL
    It seems to me that

    o your existing sewer may not be where you have marked on the drawing.

    o your new plumbing will need a vent through the new roof

    o it is common to run sewers under houses, and that your proposed path would be something more likely to be chosen if adding the sewer after your addition had already been built. You proposed route still must run the sewer under or through the foundation anyway.

    Non-pro, and my observations are based on places that freeze. Calif may be different.
    Last edited: Mar 27, 2014
  8. Leah F.

    Leah F. New Member

    Messages:
    6
    Location:
    Orange County, California
    To answer dj2, the line is 5 feet from the right side.

    Yes, thank you, dj2, HJ said how many feet I have to have the pipe from the footing. And I see that the footing of the proposed addition is on top of where the existing sewer pipe leaves the house. So I guess the sewer pipe would be zero inches from the footing of the addition which is no good, for many reasons. I am trying to confirm my understanding.

    And Reach4 said that it is not unusual to run the sewer line under the house, so I could change where the sewer enters the house to accommodate the addition?

    Can anyone describe how you add a sewer entrance to an existing house for a raised foundation? Do they dig straight down and under the stem wall?

    Thanks again.

    Leah
  9. Reach4

    Reach4 Active Member

    Messages:
    2,229
    Location:
    IL
    I don't think you said if the existing house was on a foundation. If it is on a slab, that could change things. In any case, I would want to minimize any digging under the existing house.

    I am pretty sure that you would not want you new foundation to be right on top of the line north of your toilet. Maybe make the addition wider?

    I have marked up a portion of your drawing with some lines for discussion. I would consider intercepting the existing line with paths along the red or orange. You want to install cleanouts while you are doing this. That intersection in the yard would be one good place to have a cleanout for future rodding.
    huge3.jpg
    My sketch is not trying to say how you should do it, but it might facilitate discussion.
  10. Leah F.

    Leah F. New Member

    Messages:
    6
    Location:
    Orange County, California
    Reach4,
    Thank you for your ideas. I'm wondering if there a structural reason to minimize digging under the existing foundation wall (this is a raised foundation) or is it monetary?
    Leah
  11. Reach4

    Reach4 Active Member

    Messages:
    2,229
    Location:
    IL
    The reason I would avoid most trenching under the existing house is monetary. Digging a trench in an existing crawl space is hard. If I were going to pass a single pipe under a foundation, I would see if the foundation includes piers that are heavier than the bulk of the wall. If it has piers, I would figure they are carrying the critical loads, and I would not be so worried about tunneling away from the piers. As for tunneling under at roughly right angles, I don't know. I would think about it. If I did it, I would keep the trench as narrow as possible. I would would fill the dirt back with a sledge hammer or similar with care to not damage the pipe. Maybe I would fill in the trench near the foundation with concrete. Concrete seems best to me at the moment, but I would get advice from a foundation-knowledgeable person... and I am not one.

    I would definitely not put a foundation over the top of a length of sewer as it looks like you planned to do north of the existing toilet.
  12. Leah F.

    Leah F. New Member

    Messages:
    6
    Location:
    Orange County, California
    Thank you, Reach4,
    I have definitely scrapped the plan of building the foundation over the sewer line after hearing from Terry and yourself.
    I guess I was thinking of moving the pipe because I can't widen the addition and I am hoping not to have to shrink the addition by the necessary 2 or 3 feet as explained by hj. I like the thought of going into the addition to tie into the existing sewer and I might have to decide to go with a smaller addition. I will continue to search more to find out how expensive it is to install a new sewer pipe at right angles under a raised foundation so's I can know my options. Maybe someone here has done something like that in a raised foundation with piers like I have?
    The existing pipe goes under the foundation at right angles--maybe put there when the house was built.
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