Sprinkler systems for commercial buildings are mandatory. They're not required in new home construction but a NIST study says that, above a 100 percent reduction in civilian deaths, they make economic sense.
According to NIST, the cost in 2005 dollars for adding a multipurpose network sprinkler system to a house under construction was approximately $2,075 for a 3,338-square-foot colonial-style house, $1,895 for a 2,257-square-foot townhouse and $829 for a 1,171-square-foot ranch house.