13-D Residential Fire Sprinkler Install

[Ian McKeown]

I am building a new house on a lot that I own.  The house has a zero lot line on one side and requires a residential fire sprinkler.  The County Fire Department will allow a 13-D system with no other upgrades or modifications.  

I have bids from contractors ranging from $4k to $12k.  Are the low bids leaving out parts that they will ask more money for?  Sprinkler heads, CPVC pipe, dedicated valve at the plumbing riser, backflow, labor, permits, warranty (no monitoring required).  Anything else that they'll come back for more money?