Plumbing – Is rerouting the waste line really necessary

plumbing

In a big home improvement projet we are planning to move the bathroom.

The plumber want to run a new waste line to the basement which imply opening a wall, removing laminate flooring, breaking concrete and digging in the home theater room! This new line would be, horizontally, 7 feet long with a 90 degrees bend and then 3 feet long before going down vertically to the old waste line in the basement.

Of course I would like to avoid all this work and would rather use the existing waste line. I believe we could align the toilet to fit between the floor joist and run a straight 14 feet long waste line to the old waste line. I have a dropped ceiling in the basement and there is a minimum of 8" of clearance and almost 12" near the old waste line. IMHO running this new line would be much more easy and there should be enough clearance for a slope of 1/4" per feet.

Here is some ASCII art (side view) :

                Actually              Plumber new waste line        My suggestion
                                 T           T                          T
1st floor  ======================|    =======|==============|    =======|==============|
                                 |    ,------'              |           `--------------+
                                 |    | (+3' on other axis) |                          |
                                 |    |                     |                          |
Basement   ======================|    |=====================|    ======================|
          <----------------------'  <-+---------------------'   <----------------------'

Plumber said this is "patchwork" and he refused the idea. Do you believe he is right about that?

Note :

  • Venting shouldn't be a problem : there is only one floor so running the vent in the attic and inside the new bathroom walls should be easy I guess.
  • The old waste line will still be used by the kitchen sink but there won't by any additional fixtures.

Best Answer

Could be related to fixture units meaning the old line has too much stuff dumping into it to accommodate the new bathroom OR could be your proposed 14' run is too far to wet vent back to the stack (unless you're already planning on a separate vent, then it doesn't matter.

If this is a 4" stack you should be fine on fixture units (unless you have 6 bathrooms upstairs) but you could be pushing the limit on wet venting at 14'. Therefore, run your waste line into existing as you suggest and then run a 2" vent out the back of the closet bend. In your illustration the plumber's proposal on the opposite wall would need a vent anyway so I assume it is going vertically? Run the 2" up that chase instead. I may be missing the boat here, hope this helps.

Personally, I'd redesign the bath to avoid dynamiting the home theater and digging a mine shaft down to the main, that is guaranteed to end in tears.

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