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R-49 is the common target for the roof or ceiling in cold and mixed climates. That is about 20 inches of blown fibreglass, 15 inches of blown cellulose, 16 inches of fibreglass batt or about 8 inches of closed-cell spray foam. Air seal the ceiling plane before adding any of it.
Blown-in insulation is priced two very different ways. In an open attic it is sold by the bag and blown loose to a depth; in finished walls it is dense-packed through holes drilled in each cavity. Pick where it is going and this prices the bags, the labor and the patching.
With these inputs:
| Result | Value |
|---|---|
| Installed blown-in cost | $2,124 – $3,372 |
| Cost per sq ft | $1.77 – $2.81 |
| Bags | 108 bags |
| Settled depth | 13.6 in for R-49 |
| Material | $1,404 – $2,052 |
| Labor | $720 – $1,320 |
Fiberglass or cellulose?. In an attic both work, and contractors charge similar prices for either. Cellulose is denser, resists air movement better and gets more R per inch; fiberglass is lighter, does not absorb water and settles less. The bigger price difference is DIY: cellulose bags are cheaper, but you need more of them, so compare the bag counts above rather than the shelf price. In closed walls, dense-pack cellulose is the usual choice because packing it to about 3.5 lb per cubic foot stops it settling and blocks air flow through the cavity. It needs a high-pressure blower and a fill tube — the free machines lent with bag purchases are built for loose attic fill and will not dense-pack a wall. Drill-and-fill: what to expect. Installers either remove a course of siding or drill through it and plug the holes, or drill 1–2 inch holes from inside and patch them. From inside, budget for patching and repainting every wall. Before any wall is filled, check for knob-and-tube wiring, which should not be buried in insulation, and for signs of water getting into the wall. 2026 cost guides put contractor dense-pack cellulose in walls at roughly $1.50–$3.00 per square foot of wall, with some regional quotes up to about $4 — the default range here is $1.40–$3.40 depending on material. Attic blown-in runs roughly $1.00–$1.80 per square foot installed in the same guides. Sources consulted: Angi, HomeGuide and HomeAdvisor blown-in insulation cost guides (2026 data); manufacturer coverage charts for loose-fill cellulose and fiberglass.
Attic bags = R to add × area ÷ bag rating × 1.10 · Wall cavity volume = wall area × 0.88 (framing) × stud depth · Wall bags = cavity volume × dense-pack density ÷ bag weight × 1.10 · Pro walls = wall area × $1.40–$3.40 per sq ft installed, + patching if drilled inside
| Attic | Bags | Installed cost |
|---|---|---|
| 800 sq ft | 72 | $1,416 – $2,248 |
| 1,000 sq ft | 90 | $1,770 – $2,810 |
| 1,200 sq ft | 108 | $2,124 – $3,372 |
| 1,500 sq ft | 135 | $2,655 – $4,215 |
| 2,000 sq ft | 180 | $3,540 – $5,620 |
Adding R-49 over a bare attic floor. Air sealing and old-insulation removal are priced separately in the attic insulation cost calculator.
| Material | 2×4 wall (3.5 in) | 2×6 wall (5.5 in) |
|---|---|---|
| Blown-in fiberglass | R-14 | R-22 |
| Blown-in cellulose | R-13 | R-20 |
| Blown-in mineral wool | R-13 | R-21 |
Cavity R-value only; studs conduct heat, so the whole-wall figure is lower.
Adding R-49 to a bare attic floor is roughly $1.60–$2.50 per square foot installed in this calculator for fiberglass and $1.80–$2.80 for cellulose at retail bag prices (contractors buying in bulk often land lower), and about $1.00–$1.80 DIY. Published averages of $1.00–$1.80 usually assume a smaller top-up. Dense-packing closed walls is about $1.40–$3.40 per square foot of wall with a contractor.
Multiply the R-value you are adding by the area and divide by the bag's rating: about 600 R·sq ft per 19 lb bag of GreenFiber-style cellulose (its chart: 12 sq ft per bag at R-49) and about 1,950 for AttiCat-style fiberglass. 1,000 sq ft at R-49 is roughly 90 bags of cellulose or 28 of fiberglass, with 10% extra.
Yes — that is drill-and-fill. Holes are drilled into each stud bay from outside or inside, and cellulose or fiberglass is dense-packed through a fill tube. Fire blocks and horizontal framing mean some bays need a second hole.
In an open attic, yes — with a helper feeding the machine, a mask, and baffles installed at the eaves first. Dense-packing walls is harder to do well, and poorly packed walls settle and leave cold gaps at the top.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.