If I want to run a 3" toilet drain horizontally for 17' in between TJI floor joists, how much the drain pipe will drop? I don't know how deep the plumbing pipe will be just under the toilet closet flange (Starting point) of 1/4" per foot slope. I need to decide if I need 16" TJI or 14" TJI. This floor is on second story floor supported by columns, basically exterior floor, no floor under neath. It also needs R-30 floor insulation in the TJI.
If you can tell me all the components under the toilet closet flange will be helpful.
Thank you!

using a 3 x 4 pvc spigot closet flange will be fine.
the male end can be cut or left alone.
the OD of the 3 inch hub is 4 inches.
the total drop in the pipe will be 4 1/4 inches, so used the way it is, the bottom of the pipe at the far end will be about 10 1/2 inches...
the components you will use depends on type of and location of fixtures.
the toilet will need a 2 inch vent and that vent can be used for the lav drain (wet vent)
so bottom line is you have plenty od drop and you have multiple piping diagrams.
[hdsupplysolutions.com]

Thank you for your response. Looks like 14" TJI will be sufficient. With the pipe covered in insulation still can be installed.

The plumber came today for other reason thought running 17' horizontal was not good idea. But there will be a vent somewhere along the line should push the solid. I would think.



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