Water main size for 3 family houses in new york city

[FC8]

We are installing the water main in 3 family residential house. The water line is 1.5", & there is a 2" sprinkler line in mechanical drawing. It also requires a 4" water main.

My question is, can we branch out the sprinkler lines from the domestic water line, so that we can use a 2" water main (which will save some money)?

The total sprinkler heads in the building is less than 10 pieces. They are all located in the hallway.

 

[BobPE]

FC8:

Having worked in NYC, there are a lot of approval processes that went into that drawing. I would not change anything that that drawing shows since it is someone elses liability. If you do change the design, it becomes your responsibility, and getting approval by all the agencies involved also becomes your responsibility. You can't look at this problem by rational hydraulics, even though you may be right in your thinking.

BobPE