Adding a dual sink

[phishfood]

Originally Posted by havasu

I'm sorry, but that explanation got me dizzy! By chance are there any pictures of your description? I did understand the stud drilling, but would a non-load bearing wall need dual support as well? I guess Brad's dual sink job is on the outside, and my dual sink is on an interior wall.

The code that I am familiar with states that a load bearing stud can be drilled to no more than 40% of it's thickness. Since most exterior walls are load bearing, I assume that such is the case for Brad's situation. Non load bearing walls can be drilled to 60% of their thickness, as MIGHT be the case in your situation. Find out before you break out your drill, as in some cases interior walls are used to hold up a lot of weight.

As far as the sizing and arrangement of the drain piping goes, try to look at it this way. The drain pipe leading from the stack to the trap underneath the lav needs to do two things. Take away the water that is drained out, and allow air to get back to the trap. If the pipe is too small, it doesn't have the room necessary to do both, and the system will malfunction. So, if you add second source of drain water to the pipe, you need to increase the size of the pipe so that the drain pipe can still do both things. But, if the stack is between the two drains, the water is routed to the stack by two separate horizontal pipes, that can both be of a smaller size than if both drains ran through the same horizontal pipe. Make sense?

And no, I don't have pictures, and even if I did, my connection would take a month to upload them.

[havasu]

That makes sense now. I appreciate your input on this!

[BRad704]

I think I would survive by doing what I drew up below. We would never be in a situation where we'd both be blasting the water at the same time anyway... So its not really additional volume load, its just hitting the trap from a different source sometimes...

[phishfood]

That will work. Similar to the way some double bowl kitchen sinks are piped. Some things to consider, though.

You very well might not have the space neccesary to do this. If the drain arm comes out of the wall too high, there will not be enough room between the top of the trap and the bottom of the drain body to install the wye fitting. If there is enough room, then you have to find a fitting to turn 90 degrees out of the drain body of the new lavatory. There is a compression 90 made that would do this, but I wouldn't reccomend that you use it. With the expansion and contraction cycles caused by hot drain water warming up the pipe, and then cooling down, there is a potential for the fitting to slip on the tailpiece of the lav drain, dumping a whole lot of water into your cabinet.