Open-cell rate. Open-cell foam costs $0.44 to $0.65 per board foot installed. It is the more affordable option and the right pick for interior walls, conditioned attics, and sound-dampening applications where moisture resistance is not the main concern.
Closed-cell rate. Closed-cell runs $1.00 to $1.50 per board foot. It delivers R-6 to R-7 per inch, acts as its own vapor retarder, and adds structural stiffness to walls and roof decks. For exterior assemblies in SWLA, it is almost always the correct technical call.
Thickness multiplies the number. A 1,500-square-foot attic sprayed at 2 inches is 3,000 board feet. At closed-cell rates, that is $3,000 to $4,500 in foam before labor, setup, and cleanup. Bump it to 3 inches to meet code and the number climbs again.
R-value requirements. Louisiana residential energy code targets R-19 on roof assemblies. Closed-cell at R-6.5 per inch gets there at 3 inches; open-cell at R-3.7 per inch needs close to 5 inches. More inches means more board feet means higher cost.
Access and condition. Old insulation to remove, tight rafter bays, ductwork in the spray zone, or moisture-damaged framing all add labor time. A clean, empty attic is the cheapest attic to spray.
Mobilization savings. Scheduling the attic and crawl space in one trip keeps setup costs down. Two separate visits cost more than one that covers both areas at once.