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For a garage addition, can I run a 4" main through a 2 x 6 wall to connect with the house main

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I am converting one side of my two car garage into a studio that will have plumbing for a full bathroom and kitchen sink. As the studio will be on the far side of the garage, I will need to run the main sewer line across the remaining garage space and wanted to run in a wall versus jack hammering up the concrete floor. I would also need to raise the studio floor to accommodate the plumbing.

Perhaps I only need to run a 3" to the main?? It will be 15' from the bathroom and kitchen studio addition

Thank you


asked in Interior Walls by return6 (140 points)
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1 Answer

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Hi Mary,
3’ diameter drain is a minimum required to handle a toilet and sufficient for a full bathroom (for gravity systems). You other option would be to use low profile "Up-Flush" sewage lift pump system (example: http://www.accentshopping.com/product.asp?P_ID=150032#tabtop). It supports two additional connections like sink and a shower / tub and uses 2” diameter discharge pipe.

There might be a problem with 2x6 framing of your wall. If this is a bearing or exterior wall you can only drill a hole in the stud up to 40% of its width (no closer than 5/8” to the face of stud) or notch 25% of it. 60% boring is permitted on bearing walls only if you double the stud and you cannot go through more than 2 doubled parallel studs. For non-bearing walls, 40% notch and 60% boring is OK for the entire wall.

With 2” diameter pipe bearing / exterior wall wouldn’t be an issue.

For 3” or larger gravity drain you need minimum slope of 1/8” per foot. Don’t forget venting of this system and make sure you always check your local code requirements.
answered by darekrudy (21,730 points)