Convert single sink to double sinks given narrow stud thickness

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Jian

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I am remodeling an old bathroom and trying to convert single sink to double sink drains. The old drain system is 1-1/2 inch copper pipe. The stud thickness is 2-3/4 inch instead of the standard 3-1/2 inch.

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I have read several posts on this forum and is thinking to convert to the design below. I would need drill holes through stud for the design. Given the 2-3/4 inch stud thickness and the code only allows max of 60% for non-bearing wall, it means the maximum hole that I can drill through is 1.65 inch. However, the standard outer diameter for 1-1/2 inch PVC pipe is 1.9 inch and is going to be larger than the code allowed hole size. Any suggestions how to get around this issue?

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One idea I have is that I could keep using copper as the drain pipe as the outer diameter for 1-1/2 copper is only 1.625 inch and will fit the 1.65 max limit stud hole. But ideally I would like to replace copper drain pipe with PVC.
 

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Reach4

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Are these sinks over a vanity cabinet? If so, you could bring some pipes out of the wall to be hidden by the base. There are shielded couplers that can convert 1-1/2 copper to 1-1/2 PVC -- back and forth as needed.

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Jian

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Are these sinks over a vanity cabinet? If so, you could bring some pipes out of the wall to be hidden by the base. There are shielded couplers that can convert 1-1/2 copper to 1-1/2 PVC -- back and forth as needed.
Yes, eventually there will be cabinets and vanity top. I could bring the pipes out of the wall and hide them under the cabinet. But I still hate to expose them outside.
 
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Reach4

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Hate? You can build out the wall with furring strips if you want more space in the wall.
 

wwhitney

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For the simplest layout, how many studs would you have to penetrate? I was going to suggest using 1-1/4" pipe for the trap arms, but it appears Massachusetts requires a minimum 1-1/2" trap.

Cheers, Wayne
 

wwhitney

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Also, what is the center-to-center measurement on the two lavs, and where does the existing san-tee lie within that measurement?

Most likely, Tuttle's solution will be the simplest, put a san-tee in the stud cavity behind each lav, run the drains into the floor framing and combine them there, and connect the vents higher in the wall, using a 1-1/4" vent (PVC or copper) for any vents that have to penetrate a stud.

Or run the vents up into the floor framing or attic above, and connect them there. Since you'd be putting a hole in the top plate that is over 50% of the width, it would be good practice to reinforce the top plate with a metal strap (but if I recall only required for bearing walls).

Cheers, Wayne
 
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Jian

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Also, what is the center-to-center measurement on the two lavs, and where does the existing san-tee lie within that measurement?

Most likely, Tuttle's solution will be the simplest, put a san-tee in the stud cavity behind each lav, run the drains into the floor framing and combine them there, and connect the vents higher in the wall, using a 1-1/4" vent (PVC or copper) for any vents that have to penetrate a stud.

Or run the vents up into the floor framing or attic above, and connect them there. Since you'd be putting a hole in the top plate that is over 50% of the width, it would be good practice to reinforce the top plate with a metal strap (but if I recall only required for bearing walls).

Cheers, Wayne

Thanks for the reply! The existing san-tee will be the center, and the new left lav will need penetrate one stud and right lav will need first penetrate one stud and then one double stud.

I agree with you that Tuttle's solution might be the best depending on the direction of my floor joints. I am still in the process of demo and will open the floor eventually. My guess is the floor framing direction is orthogonal to the drain pipes, so notching of floor framing might be needed to combine the two new drains together. Anyway it is still good news that I can accommodate 1-1/4'' vent pipes to the narrow stud width without breaking the code.
 
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