Standpipe System

[MTuWThFriFriFri]

Hi!
I have questions. I am designing fire protection system
for 4 story high condominiums in Los Angeles Area.
According city code in the area, there is a requirement to add standpipes in addition to overhead sprinkler system to provide sprinkler coverage.This is first time for me designing standpipe combined with overhead sprinkler system. According to NFPA, for Class I Standpipe,
resisdual pressure of 100 psi is required flowing 500 gpm
at the most remote hose connection and 250 gpm for each
additional standpipe up to 1250 gpm. There are 3 stairway
shafts separated approximately 100 ft from each other.
From my calculation, I estimated 4" supply line to meet
this demamd. I have left out overhead water demand from the standpipe calculation. Am I in the right direction as far as sizing supply line?
According some source, I need to include overhead flow demand into standpie calculation...

Nathan

 

[TravisMack]

The standpipe demand is a separate calculation from the overhead sprinkler system, so you are correct in that regard.

Your required demand will be 1000 gpm if you have only 3 stairwells (500+205+250). A 4" supply line will be tough to carry that amount of water any distance at all. You can probably figure a 6" supply, then reduce down to 4" for each riser.

However, without knowing the kind of pressures you have available, that is just a guess.