twd22285
You are talking about the one pipe that a number of systems are fed off of??? right????
my answer to your last question would be you do not have to run a seperate underground main for each riser.
So if say your building had eight risers, option of running one underground to the manifold or running eight seperate underground mains to each individual riser. AS in saving money.
The though is you only have one fire in the building at a time, so the one underground can meet the demand of the most demanding system.