Attic Insulation Cost Calculator

Stick a ruler through the insulation down to the wood and read the depth, then multiply: blown fiberglass is ≈R-2.5 per inch settled, blown cellulose ≈R-3.2, batts ≈R-3.2. So 6 inches of fiberglass is about R-15, and the classic sign you're under-insulated is joist tops peeking through — that means less than ~7 inches up there. The calculator's depth input does this math for you, and the bill follows the ruler: from that 6-inch reading, reaching R-49 prices at about $1,889 on a 1,000 sq ft attic with air sealing in this model, while a bare-joist attic runs roughly $1,532 to get only to R-38.

From a typical 6-inch fiberglass start (≈R-15), a 1,000 sq ft attic runs about $1,389 for the blown cellulose alone, or $1,889 with the air sealing that should ride along with it. That lands inside Angi's published $1,700–$2,500 typical attic range and HomeGuide's $1.00–$2.80 per sq ft installed. Starting from bare framing instead costs about $1,532 just to reach R-38.

On the same R-15→R-49 top-up over 1,000 sq ft, this model prices blown cellulose at $1,889 and blown fiberglass at $1,983 — about $93 apart, because fiberglass's lower R-per-inch means roughly 3–4 more inches (and more bags) to hit the same target. The real differences are physical: cellulose is treated with borates for fire and pest resistance, fills gaps and corners more completely, and cushions better around wiring; fiberglass doesn't settle and stays fluffy at full depth. Most retrofit crews quote both and the choice usually comes down to which supplier services their blower.

Yes — it's the cheapest energy dollar in the whole job. Warm indoor air leaks through top plates, wire and plumbing chases, can lights and the hatch; insulation slows conduction but does almost nothing against moving air. Crews charge roughly $500 per 1,000 sq ft (this model prices $0.50/sq ft, mid-range of HomeGuide's $350–$3,000), and on this default job it adds about $500 — worth it before the first bag is blown, because you can't reach those leaks afterward.

Usually yes. Baffles ($0.22/sq ft here, ~55 chutes on a 1,000 sq ft attic, about $4 each installed) hold the blown material back from the soffit vents so air can still wash up the underside of the roof. At R-49 depths the new insulation is 14+ inches deep — deep enough to bury every eave vent on the house if nobody pins chutes in first. With a foam-sealed roof deck they're unnecessary because the assembly is unvented by design.

When the ductwork and HVAC live in the attic, or you plan to finish the space — foam brings the ducts and the attic inside the conditioned envelope, which floor insulation can never do. Our model prices a 1,000 sq ft attic at the R-38 roof deck around $8,358, versus roughly $1,889 for the floor top-up. It's 3–5× the money for a problem floor insulation doesn't solve; if your ducts are in the basement, stick with blowing the floor.

A two-person crew blows 1,000 sq ft plus air sealing in a half day; difficult access (low pitch, no walk boards, cramped hatch) can double it — this model prices that at about $2,371 versus $1,889 for easy access. DIY blowing is the classic homeowner job: materials alone run about $751 here, so a turnkey quote of $1,889 means roughly $1,138 is labor and rig time — rental blowers are often free with a minimum bag purchase. You supply the hatch trips, the helper and the dust.

Vacuuming out old contaminated insulation ($1–$3 per sq ft when it's needed), knob-and-tube wiring remediation, mold or rodent cleanup, duct sealing and duct insulation, raised-collar or knee-wall detailing, and structural work around the hatch. Permits are rarely required for attic-floor insulation, but exposed spray foam needs an ignition/thermal barrier in most jurisdictions — and 2026 federal efficiency-credit rules changed, so price any rebate at $0 until your utility confirms one.