Fiberglass batts are usually the cheapest per square foot, open-cell spray foam is the most expensive, and the real variable is labor, not material. For an average US home, expect $0.35 to $0.65 per square foot for blown-in fiberglass at R-30 to R-49, $0.75 to $1.50 per square foot for closed-cell spray foam at R-13 to R-21, and $0.50 to $0.90 per square foot for dense-pack cellulose at R-35 to R-40.<\/p>\n
The per-square-foot rate is always a range because it bundles three things: the insulation material, the labor for installation, and any prep work like air-sealing or removing existing batts. The material alone is a small slice of the total. Fiberglass batts by the roll cost $0.05 to $0.15 per square foot of R-13 to R-30 material<\/strong>, but installing them at R-49 depth over an attic floor usually lands between $0.35 and $0.65 per square foot installed<\/strong>.<\/p>\n Two variables dominate the installed price, and they explain why two quotes for the same job can differ by 40 percent. First, depth<\/strong>. R-49 in an attic is roughly 14 to 16 inches of blown-in material, and each extra inch of depth adds material and labor at a near-linear rate. Second, access<\/strong>. An attic with a ladder, a dry floor, and no existing batts to work around is cheap. The same square footage through a tight kneewall, a joist bay with 2×6 furring strips, or a crawl space with a 2-foot clearance runs 30 to 50 percent more per square foot because the crew has to cut, fold, and fight for space.<\/p>\n Season also moves the number. A contractor running a full crew from November through February will quote more per square foot than one working in a slow June week, because demand for cold-weather insulation jobs peaks when the heating bill does. If you are getting quotes from November onward, treat the low side of the range as the realistic floor, not the expected number.<\/p>\n “Dense” is a marketing word. The two numbers that actually price the job are density<\/strong> (pounds per cubic foot of blown-in material) and R-value at the installed depth<\/strong>. Dense-pack cellulose at 3.2 to 3.5 pounds per cubic foot is the standard for a moisture-driven wall; it costs more per square foot than the same cellulose at 2.2 pounds per cubic foot because the denser pass takes longer to pump and settle. The number to hold a contractor to is R-value at depth: a quote that says “R-49 cellulose” but does not name the target depth or the post-install measured R-value is a range, not a specification. The “what home insulation actually is<\/a>” guide breaks the R-value definitions down by type, so you can check whether a quoted R-value matches the material depth they plan to install.<\/p>\n One quick sanity check: if a quote for an attic insulation job comes in at under $0.25 per square foot installed<\/strong>, it’s almost certainly not including air-sealing and the R-value is lower than advertised. The attic insulation types and cost guide<\/a> walks through the same R-value definitions with depth examples.<\/p>\n The one question that separates a real quote from a lowball: “What’s the installed R-value at the depth you’re proposing, and is air-sealing included?”<\/strong> A quote that only names a material (“we’ll do fiberglass”) without a target R-value and depth is a range, not a price. Ask for the per-square-foot price, the target R-value, and whether the top-plate gap and eave air-sealing are in the scope<\/strong>. If the answer is “we’ll just use standard batts,” that’s a red flag for a job that won’t actually fix the moisture or heat loss you’re trying to address.<\/p>\n\n\n
\n \nType<\/th>\n Typical R-value per inch<\/th>\n Installed $\/sq ft<\/th>\n When it makes sense<\/th>\n<\/tr>\n<\/thead>\n \n Blown-in fiberglass (loose-fill)<\/td>\n R-3.0 to R-4.0<\/td>\n $0.35 to $0.65<\/td>\n Attic floors, existing homes, over the top of old batts<\/td>\n<\/tr>\n \n Closed-cell spray foam<\/td>\n R-5.5 to R-7.0<\/td>\n $0.75 to $1.50<\/td>\n Sealed attics, crawlspace ceilings, new construction<\/td>\n<\/tr>\n \n Dense-pack cellulose<\/td>\n R-3.5 to R-4.0<\/td>\n $0.50 to $0.90<\/td>\n Existing stud walls, high moisture-driven climates<\/td>\n<\/tr>\n \n Open-cell spray foam<\/td>\n R-3.5 to R-4.5<\/td>\n $0.45 to $0.75<\/td>\n Vented attics where a Class I vapor barrier is on the warm side<\/td>\n<\/tr>\n \n Fiberglass batts (R-13 to R-19, stud walls)<\/td>\n R-13 to R-19<\/td>\n $0.40 to $0.65<\/td>\n DIY stud-wall fill, retrofit of a 12×16 room<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n What Moves the Number Most<\/h2>\n
Density, R-value, and the Two Numbers That Matter<\/h2>\n
What to Ask a Contractor Before You Commit<\/h2>\n