Love the site and have learned so many things reading through the forum. About to start work on a garage with living space above it and wanted to get everyone's opinion on getting water out to the new building.

Main house was built in 1949. House is one story on a hill with a walk out basement under about 1/3 of the house. The rest is crawl space. I spent some time this last week digging (always fun in a crawl space) to get a better idea of the current plumbing setup. Here's what I know.

Main line into the house is 3/4. That line passes to the back half of the house about 18" below grade about 30'. There are 1/2" branches as it passes my kitchen (sink, ice maker), hall bath (lab, toilet shower/tub), laundry and master bath (double lav, toilet, shower). At the end of that run is the tankless water heater and the 3/4" hot line runs back to the front of the house with 1/2" branches at the same locations (master bath, laundry, hall bath and kitchen.)

My question is two-fold.

Our GC and plumber want to tee off the end of the cold line, near the water heater, and run 3/4" to the new structure (about 50' away). In my head it makes more sense to tee off where the 3/4" enters the house and send one side to the main house and one side to the new building. I don't have any science/facts to back up that assertion - it just seems to make more sense to me - but then again I'm not a plumber. I'm just getting the impression from the GC/Plumber that their way would be 'easier' but I don't know if it's better or correct.

The second part of that question: is 3/4" even large enough to carry that many fixtures? The new building will have one bath (lab, toilet, shower).

Any help/advice would be greatly appreciated.