3/4 or 1/2 inch copper pipe?

[hovrens]

My plumber flaked on me to plumb my room addion. I'm adding a half bath (1 sink and 1 toilet) in a new room addition on a slab on grade foundation. Prior to the plumber flaking he said he would tap in to a nearby bathroom 3/4" pipe and run 1/2" to new bathroom. Sounded good!!!

I have a friend who just plumbed his new addition and taped in to a pre existing 1/2" pipe and ran new 1/2" pipe to his new bathroom. He said it was unneccessary to have to tap in to a 3/4" for the new bathroom.

I considered him to plumb my addition but need verification on his theory before I can trust him. Anyone have input???

[Tom R]

I'm much more of a carpenter than a plumber, but here's my two cents anyway. I would think you want your main run to be 3/4", - - then reduce to 1/2" fairly close to the bathroom, - - 3/4" to 1/2" translates as volume to pressure.

[roger g]

half inch is enough. They still do complete houses in half inch for years without too much problem. As your addition only includes a toilet and a sinl any problem that are usually associated with possible low pressure ( flushing when someone is taking a shower)doesn't apply to you.

roger

[VALENT]

In your case tapping into the 3/4 in existing line makes good sense. Run off of it with 1/2 inch and you shouldn't have problems with either bathroom. Plumbing the main run with 3/4 may allow a decrease in pressure and volume(which may be noticeable) in your existing bath. I really dont think it will but 1/2 in will be plenty good.