Michael,
I know this is a very old post but I just noticed it. Do you have the same opinion today?
Doesn't running 3/4'' to multiple fixtures have the opposite consequence? Even at 1/2'', if multiple fixtures go off at once, won't you notice water pressure loss? The water system can only hold so much pressure, no?
I know that you're worried about loss in water pressure when multiple fixtures are used together but 1/2'' would actually be the optimal size. And, even 3/8'' for small sinks. For example, 1/2'' already is big enough to supply 10 faucets running at once. So, doesn't the code here already consider the likelihood of multiple fixtures going at the same time?
You also have the benefit of reducing hot-water consumption as well as the time that the hot water gets to the tap, no?
By the way, I'm sorta' new to this so just learning right now. I'm curious to know what the optimal pipe setup is.
I DESPISE MANIFOLDS. I do all of my repipes by running a gutline (both hot and cold) the full length of the house. I extend my 3/4" (or 1") gutline to the end of the run. So if the end of the run is a bathroom. I'll take that 3/4" all the way to the tub. The last fitting I use on the end is a 3/4 x 1/2 x 1/2 tee. I cut everything else in full-size using 3/4 x 3/4 x 1/2 tees.
yes, I oversize the system on purpose. On some repipes, we'll make a giant loop with 3/4" red pex and 3/4" blue pex. What I'm trying to avoid is you in the shower, then your wife flushes the toilet. Or you in the shower, and then your wife decides to run a load of laundry. MORE IS BETTER. Remember, the plumbing code is THE MINIMUM STANDARD. Don't know about you, but minimum standard isn't good enough for me.