When to add domestic demand to sprinkler calcs

[skdesigner]

"Also, I hope the designer would have included the plumbing fixures in the hydraulic calcs for the system"

This quote from thread184-285666 prompted an OH SH*T moment in my office. Looking through NFPA 13 2010, I see:

A23.1.3.2
When a single main less than 6" in diameter serves both domestic and fire systems, the domestic demand should be added to the hydraulic calculations for the fire system at the point of connection unless provisions have been made to isolate the domestic demand.

So far so good. I have yet to design a 13 system with less than a 6" incoming main.

Considering the occupancy being discussed in the previous thread (mall complex), it seems unlikely that the incoming main would be less than 6". To me, the quote is saying that ALL calcs with a combined service main need to include the plumbing fixtures.

Thanks in advance for the help!

 

[skdesigner]

Thought this would have been more of a "geez skdesigner, you add domestic demands in x and y, but not in z scenarios. Everyone knows that" kind of answer.

I add domestic flows to my calcs in 13R systems, and when the >6" underground serves both domestic and sprinkler, but am I making a big mistake by only calculating the sprinkler requirements when the supply is 6" or greater?