Ok to branch a pipe from bathroom sink to kitchen sink?

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Old 09-07-17, 09:10 PM
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Ok to branch a pipe from bathroom sink to kitchen sink?

I've hired a contractor I found on AngiesList to add a kitchen to my house. However I'm not sure he doing things right. The way he explained it to me was that in order for the kitchen sink plumbing to be installed he will have to merge it with the bathroom. In other words he plans to branch off the water supply lines from the shower and run them into the kitchen sink, the same with the drain pipe. However I'm concerned on what effect that will have on water pressure? Is there enough pressure in the shower supply line to supply 2 sinks in the kitchen? Are there some kind of guidelines to follow? And same for the outflow pipe, does he need to consider capacities, if so which ones and how are calculated? I just want to make sure he's not some croc that will try to do it the cheapest way for him. Is this something that is usually done? If not where does he have to draw the water supply lines and the drainage lines from? Thanks.
 
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Old 09-08-17, 04:41 AM
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I'd be more concerned about the drains than the supply lines when using both sinks at the same time. If he didn't tab off the other sink, where else would he have been able to connect the pipes?
 
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Old 09-08-17, 09:37 AM
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If thats the only place he can tap into then its common place to do so.

Water lines are one thing.. If you have city water it shouldn't have a pressure issue. If its a long run Maybe you would want to find a closer 3/4 line to tap off of..

As far as the waste line, if he does tap into the bath sink, it will need to be done with a double fixture fitting, not a wye or a double san tee... And if its farther then 8 ft he will need to run a separate vent on the new additions waste arm. Most likely run the vent up through the roof of the new addition...
 
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Old 09-08-17, 05:39 PM
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I was thinking that anytime a new line is run it has to be from the water main that's entering the house. So from the basement I guess? But if that's a usual thing to do then I don't really mind, this guy is giving me a good price so it's safe and by the book I'll go with it. I was just wondering how the pressure works though? You're saying if I have city water then the pressure is sufficient but if both the sink and the shower are running they won't have to share pressure between themselves? And what if the third sinks turns on also, won't the pressure go 3 ways. Thanks for taking the time to explain, I just want to understand what he's got planned.
 
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Old 09-08-17, 06:19 PM
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If it was a brand new house being built in 2017, its conceivable that every fixture could have its own dedicated pex line that branches off of one or several large manifolds.

In reality, a remodel is not going to be done that way. If you want to keep costs down, you do what is reasonable and efficient. And when plumbers get $120/hr, that also usually means whatever is going to be the most expedient.

We don't know what size supply lines you have or how each was run, so we can't answer much more than that. In some cases a 3/4 line is run partway then it branches off to several 1/2's. In other cases everything is half... in which case it makes no real difference what you do. If your basement is finished, I doubt you want him blasting holes here and there to try and run a dedicated supply line.
 
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Old 09-09-17, 09:06 AM
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Allright, I feel a little more secure about this now. Thanks for all the help.
 
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