Insulation Calculator
Insulation R-value coverage + cost — fiberglass batt, blown-in cellulose, blown-in fiberglass, closed-cell and open-cell spray foam.
IRC R-49 in zones 5-8. R-38 in warmer zones.
Batts: 300. Blown: 1000+. Spray: 300.
Result
- Depth needed for target RAt 3.5 R/inch
- 14.0 in
- sq ft of coverage
- 1296
- Material cost
- $1,426
- Labor cost
- $165
- Total (material + labor)
- $1,591
This estimate is based on national average costs and may vary by region, project specifics, and market conditions. Use as a starting point for your bids.
How to estimate an insulation job
Insulation math is R-value × area. Pick your target R, divide by the R-per-inch of the material, and that's your depth. Multiply by area to get coverage. This calculator handles that conversion plus material + labor pricing for the five common residential insulation types.
R-value per inch by material
| Material | R/inch | Best for |
|---|---|---|
| Fiberglass batt | R-3.2 | Open framing, walls, floors |
| Blown-in cellulose | R-3.5 | Attic floors, best $/R |
| Blown-in fiberglass | R-2.5 | Attics, lower density |
| Open-cell spray foam | R-3.7 | Interior walls, sound deadening |
| Closed-cell spray foam | R-6.5 | Exterior, vapor barrier, premium |
IRC R-value targets by cavity
- 2×4 walls: R-13 (minimum, most zones)
- 2×6 walls: R-19 or R-21 (northern climates)
- Attic floor: R-49 (zones 5-8), R-38 (warmer)
- Vaulted ceilings: R-38 with 2-inch vent gap above
- Crawlspace walls: R-13 (conditioned crawl)
Pricing benchmarks (installed)
Approximate installed pricing in most US markets:
- Fiberglass batt (R-13 walls): $0.70–1.20 per sq ft
- Blown-in cellulose (R-49 attic): $0.95–1.60 per sq ft
- Blown-in fiberglass (R-49 attic): $1.10–1.80 per sq ft
- Open-cell spray foam (R-13 walls): $1.20–2.00 per sq ft
- Closed-cell spray foam (R-13 walls): $2.00–3.50 per sq ft
Spray foam includes the value of the air barrier plus vapor barrier (closed-cell), which can simplify the wall assembly and let you skip housewrap. That cost offset is real — factor it into your bid.
Frequently asked questions
What R-value do I need for my walls?
2×4 stud walls take R-13 batts (IRC minimum, most US climate zones). 2×6 walls take R-19 or R-21 (northern climates). Attic floors run R-38 in zones 1-4 and R-49 in zones 5-8. Vaulted ceilings need R-38 with a 2-inch ventilation gap. Always confirm your local energy code — some jurisdictions exceed IRC.
Spray foam vs blown-in cellulose — what's the real difference?
Spray foam (especially closed-cell at R-6.5/inch) gives you the highest R per inch and acts as an air and vapor barrier. Blown-in cellulose runs R-3.5/inch and needs separate air sealing. Cost differential: closed-cell spray foam runs $1.50–3 per sq ft per inch of depth installed; cellulose runs $0.80–1.50 per sq ft for an R-49 attic blow. Cellulose is the better dollar-per-R for attics.
How many batts do I need?
Standard fiberglass batts cover 24 sq ft each (24-inch wide × 96-inch long) when used 16-inch OC, or 32 sq ft each (16-inch wide × 96-inch long for 24-inch OC). High-density R-21 batts cover the same area. Bundle/bag counts vary — always confirm your supplier's batt-per-bag count when ordering quantity.
Do I really need a vapor barrier?
In zones 5-8 (cold climates), yes — faced batts have a kraft paper vapor retarder facing the warm side. In zones 1-3 (hot climates), no — vapor barriers actually trap moisture and cause condensation. In zones 4 and the moist parts of zone 4M, check your IRC table. Spray foam (closed-cell) acts as its own vapor barrier above ~2 inches thick.
How fast can a crew install insulation?
Batt install: 200–400 sq ft per hour for one installer in open framing. Blown-in cellulose (attic): 1,000+ sq ft per hour for a 2-person team with rented machine. Spray foam: 200–400 board-feet per hour for a 2-person crew (1 board-foot = 1 sq ft × 1 inch deep). Spray foam is the most expensive per sq ft but the highest R per labor-hour.
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