1 A complete fire sprinkler system integrated into a new construction project costs about $1 – 2 per square foot. 2  This includes equipment and installation. 3  Retrofitting an existing building usually costs between $2 – 7 per square foot. This includes equipment and installation. 2  Retrofitting an existing building usually costs between $2 – 7 per square foot. 3  Retrofitting a high rise building will run you about $2 – 4 per square foot. 4  Installing a fire sprinkler in a historic building can sometimes be more expensive – up to $10 per square foot.