Confused on supply sizing

I've seen guidlines that state that flow rates through copper pipe should be designed to NOT exceed 5-7 feet per second. Is this accurate?

If i have one supply for the following fixtures:
Whirlpool tub faucet, 4.0 units
Shower, 2.0 units
Bath/Shower, 4.0 units
2 Lavs, 2.0 units

Unit total is: 12.0
https://terrylove.com/watersize.htm

Take the whirlpool tub by itself. The faucet can flow ~15gpm @ 60psi, for 3/4" copper this would be around 10fps, 1" would be around 6fps?

If i use the code books and add up the fixture units, 3/4 is fine. But would it be more appropriate to upgrade to 1". We would never use all fixtures at the same time, but two showers at the same time would be in the plan, so that's ~5-6gpm.

I am not familiar with any code requirement that gives a maximum size for your feed. You should only be governed by min and max pressures and flow rates at the fixtures.

With a pressure regulator set to 60-80psi this should not be a problem.

Consult your AHJ and water company.

I dont know if code addresses water velocity directly, but I believe the copper develpment association ( www.copper.org) does call for velocities not to exceed the range you mentioned. It causes erosion of the pipes and fittings.

So, tub fillers that flow 10-15 gpm are pretty common. But is it common to have 1" copper supply to the tub? Also the tub valves themselves are 1/2" copper.

So my big question is, should i be putting in 3/4" or 1" copper. I forgot to mention the lenght is approximatley 35 feet.

-Whirlpool tub filler
-Shower stall
-Shower/tub
-2 lavs
-2 toilets

Thanks

If cost is no object then go with the 1". 3/4 will work fine and with the cost difference I'd not waste the $ on the 1". Is the upstream connection 1" or larger? Price it out and see if the cost is worth the lack of a little pressure loss the few times you have all fixtures running at once. The erosion factor is so minimal at the limited use of home bath fixtures that flow volume capacity would be much more important to me than velocity.

do you have a kitchen sink, laundry, hose bibs?

if you have a kitchen sink, laundry and 2 hose bibs I'm figuring 26 units. This would require a 1" building supply. Even if you don't have a laundry (4FU) a 1" would still be required. This is UPC sizing.

I'm looking at the 2000 UPC, and in appendix A, A 6.1 Velocities shall not excede 10 ft./sec. I could go out to my truck and look up the current version but that takes to much effort. Individual states may choose to adopt all or portions of the code book, and make their own amendments. So, in this case, Appendix A may or may not have been adopted.

Thanks for all the responses. This is in Illinois governed by the Illinois Plumbing code, which seems to be most closely related to the standard plumbing code.

Since the building supply size has been brought up, and you guys have been so kind already, here are my details on how i've come up with WSFU and sizing. If i'm looking at the wrong i'd really appreciate a smack upside the head.

I'm on a well, that will pump 18gpm. We are planning on 1" coming off the well tanks (so i assume the 1" is considered my building supply)

I got my WSFU from this chart: TABLE M Load Values Assigned to Fixtures
http://www.ilga.gov/commission/jcar/admincode/077/07700890ZZ9996amR.html

Then using this chart i can find the minimum pipe size TABLE N (W.S.F.U.) for a Supply System with Flush Tanks
http://www.ilga.gov/commission/jcar/admincode/077/07700890ZZ9996anR.html

Here are my fixtures with WSFU's (hopefully it formats ok)
So if i did that right, 1" building supply is good (off the well tanks in my case).

Back to the whirlpool tub filler, the code doesn't list anything specific for that type of faucet. It's has a bath faucet as i listed above with total 2WSFU, then it lists on this page http://www.ilga.gov/commission/jcar/admincode/077/07700890ZZ9996apR.html bath faucet as 5gpm, which is fine for 1/2 pipe. If you were to really count it as 15gpm and run down table N (link above) i guess i would be required use 1" supply to the tub facuet? That seems crazy to me, since the valve is only 1/2" anyway.

Thanks
-Mike

how many gpm of cold?

Mikept: Are you asking how many gpm cold for the tub faucet?

You know, i guess i'm thinking of this wrong. I've got the delta r2707 rough in valve (the delta site seems to be down at the moment so i can't find the exact specs) But, if i remember correcly it only stated 15gpm, not hot/cold. So now that i think of it, you would only expect half the gpm per hot/cold.

So if i figured 7-8 GPM per supply line, that would be 5-6 feet/sec for 3/4" copper. So by that logic 3/4" would be the correct choice?

noise

That is a sound proofing issue more than a plumbing one unless the pipe runs through the sanctuary. But in Japan, they had to install noise generators in the rest rooms because the ladies were flushing the toilets to mask any untoward or embarassing noises.

Hey..You made no mention of supply pressure but 3/4 will be fine at the 46-60 psi range.
the 1" will give a bit more volume but will you be running everything wide open at the same time? MN code figures ditance from the tap in the street to the highest fixture at a given pressure.60 - ish is pretty common in most parts of the city.A cheap pressure gauge from The Home Dumpster will squre you up on that.They have them with female hose threads.
Good luck.Sounds like a nice project!