Bathroom supply line.

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Matthew Kane, Sep 25, 2019.

  1. Matthew Kane

    Matthew Kane New Member

    Sep 25, 2019
    I have a quick question about a bath installation. I was going to run a separate 1/2 copper supply line to my toilet. Is this necessary or can I branch off my tub/shower cold line (1/2)? Everything at this point has it's own supply line off of a 3/4 copper main. I dont want the toilet flush to affect the shower.
  2. Michael Young

    Michael Young In the Trades

    Sep 20, 2016
    North Carolina
    I prefer making separate drops to where you have access to everything underneath.
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  4. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    From the UPC
    1.0 units for lav
    2.5 units for toilet
    4.0 units for tub
    2.0 units for shower

    3/4" meter and 1/2" supply at 80 feet is 6.0 units.

    Normally I would run 3/4" cold to a single bathroom with tub.
    That being said, if you're taking a shower 2.0 and flush the toilet, 2.5 then you're up to 4.5 units on the 1/2".
    Most people when filling a tub wait until the tub is full anyway before hopping in.
    Shower heads are restricted, and I hope you have a balanced or thermostatic valve for the shower. That's been code now for decades.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Modern shower valves were mandated just for the reason why you're contemplating that hook up. Prior to the advent of pressure balance anti-scald valves, that would likely result in a shot of extra hot water from your shower head when someone flushed the toilet. If the valve is working properly, you'd still probably notice a momentary decrease in overall head output as it tried to compensate for the loss on the cold line.

    It will work, but if you can pull the toilet's line off of the main feeding the bathroom group (maybe a 3/4" line?), it would have less effect on the shower.
  6. Matthew Kane

    Matthew Kane New Member

    Sep 25, 2019
    It's a whole new bathroom. I'm roughing in the plumbing now. I carried the 3/4 main upstairs and branched off of them for the 2nd bath. The room directly below is gutted also, so access isn't an issue. I shared both 1/2 hot and cold with a double vanity. When I redid the plumbing downstairs I ran all separate lines to everything also. I think I'll just run a dedicated line to the toilet too. I had to use soft copper to go through the joists. I assume all new valves are thermostatically controlled for the tub/shower?
  7. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Aug 9, 2009
    The rule I always followed is not to put two fixtures on a 1/2" line.
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