2" service line to 1" distribution line 1

[Nathon]

This is new construction. Developed length is 100'. WSFU is 26. Based on UPC Table 6-6 the building's service line should be 2" with a 1-1/2" distribution pipe.

The 2" service line is already installed, and our client is now saying he wants a smaller distribution line because of tenant changes. He specifically wants a 1" line because he says it is so much cheaper than a 1-1/4 or 1-1/2. However, the UPC table does not show a 2" service to 1" distribution. Neither does the IPC's table.

So the question is, on a 2" service line, how many water supply fixture units will a 1" distribution line deliver, at 100'? Do I just go with the 1" distribution line at 25 WSFU at 100'? Do I have a 1 WSFU allowance?

(I'm working at 30 psi because we don't know the actual pressure on site.)

Thank you for your help!!

PS - UPC table is attached.

 

[PEDARRIN2]

Sounds like a tenant finish, like a mall or something similar. I always hate those because the owners only see $$ and do not care about design except that it is eating into their profits. Typically they are just looking for a PE stamp to get their building designed. Sometimes they even get things changed in the field (not telling the engineer) so they get it built cheaper.

I don't work much with the UPC but it includes a requirement to size the water piping per the tables. So if it says 2", then you have to provide 2". IPC has its sizing in the appendix so it is not mandatory.

A 1" line is not going to be so much cheaper than 1.25" or 1.5" unless you have a lot of it, which I doubt.

Water supply is sized by flow rate, which is related loosely with fixture units. The fixture units will be correlated with a peak flow rate, which then is used to size the piping based on available pressure and pipe friction. If you are starting with 30 psig, I would highly recommend keeping the piping as large as possible or else there will be pressure and flow problems, unless the building is less than 1 level above grade. Even then, you probably would not have enough to flush toilets unless they are tank type. I would request a fire hydrant flow test to determine what exactly is the available pressure.

If this is commercial construction, then it will likely require a RPZ backflow preventer which will have a pressure drop of 10-13 psig. It will likely have a water meter which will have a pressure drop of ~5 psig. So you have already lost ~15 psig and you haven't even gotten to the pipe friction loss.

I would stick to your size and let the owner know that you are the design professional with the PE and unless he wants to get a variance, then the pipe will stay the size it is. It won't make him happy, but it will tend to shut him up.

 

[Nathon]

Pedarrin2, you nailed it. Cheap strip center. Thank you for your input!