Not many code restraints are relevant to simple extensions of hot and cold water supply lines.  In most cases you just must be sure the water pressure is sufficient. The appropriate material and diameter for supply pipes should be clearly explained in your local code, in accordance with the number of “fixture units”, which type of setting up usually uses. (A fixture unit represents 7.5 gallons or 1 cubic foot of water a minute.)
As a rule, the major supply line that leads in from the outside is ¾- or 1-inch duct, supply branches are ¾- inch duct, and risers that feed individual fixtures are ½-inch duct. If you want to discover problems with your current supply system or figure the pipe specifications for a remodel, it will be necessary to know the amount of total fixture units applied in your home. Add up the rates of all fixtures, calculate the length of the distribution ducts and then consider the chart below to define pipe size.
Do not forget that perfect duct size may differ depending on the quantity of delivered water pressure and the tallness of proposed addition. The pressure of water falls 0.5 pounds a square inch for each foot in elevation from the source (the water well), so a second- or third-story addition probably will require a bigger duct size than the one given in the chart. If your water pressure is either higher or lower, check with your local code for alternative tube sizes.
SIZING FOR WATER DISTRIBUTION PIPES
Water heater 3/4"
Hose bibb 1/2" to 3/4"
Maximum Length for Total Fixture Units (46 to 60 PSI)
Meter & Street
Service
Size of Main Supply Pipe & Branches
40' 60' 80' 100' 150' 200'
3/4" 1/2" 7 7 6 5 4 3
3/4" 3/4" 20 20 19 17 14 11
3/4" 1" 39 39 36 33 28 23
1" 1" 39 39 39 36 30 25
1" 1-1/4" 78 78 76 67 52 44
SIZING FOR WATER SUPPLY RISERS
Minimum Pipe Diameter:
Minimum Pipe Diameter:
Water Temp:
Cold Hot
Toilet 3/8"
Bathtub 1/2" 1/2"
Lavatory (sink) 3/8" 3/8"
Shower 1/2" 1/2"
Bar sink 3/8" 3/8"
Kitchen sink 1/2" 1/2"
Water Temp:
Cold Hot
Bar sink 3/8" 3/8"
Dishwasher 3/8" to 1/2"
Washing machine 1/2" 1/2"
Laundry sink 1/2" 1/2"
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