Calculate how much insulation you need, R-value requirements by climate zone, bags or rolls needed, and total cost with estimated energy savings for walls, attics, floors, and crawl spaces.
Proper insulation is one of the highest-ROI home improvements you can make. It reduces heating and cooling costs, improves comfort, reduces noise, and increases property value. Yet many homes — especially those built before 1980 — are severely under-insulated. This guide helps you calculate exactly how much insulation you need and choose the right type for your application.
| Zone | Cities | Attic | Wall Cavity | Floor |
|---|---|---|---|---|
| Zone 1 | Miami, Honolulu, Key West | R-30 | R-13 | R-13 |
| Zone 2 | Houston, Phoenix, Jacksonville | R-38 | R-13 | R-13 |
| Zone 3 | Atlanta, Dallas, Los Angeles | R-38 | R-13 | R-19 |
| Zone 4 | DC, NYC, Seattle, Memphis | R-49 | R-15 | R-19 |
| Zone 5 | Chicago, Boston, Denver | R-49 | R-20 | R-30 |
| Zone 6 | Minneapolis, Burlington, Helena | R-60 | R-21 | R-30 |
| Zone 7 | Duluth, Anchorage, International Falls | R-60 | R-21 | R-30 |
Blown-in cellulose is recycled newspaper treated with borate fire retardant. It's the best value for attic floors — it fills gaps, conforms to irregular spaces, and provides excellent sound damping. R-3.5 per inch. Cost: $0.50–$0.80/sq ft installed. Blown-in fiberglass is lighter and doesn't absorb moisture, but provides lower R-value (R-2.5/in) and doesn't air-seal as well as cellulose.
Fiberglass batts are the most common wall insulation — pre-cut to fit standard stud cavities (3.5" for 2×4 walls = R-13, 5.5" for 2×6 walls = R-19). Cheap and DIY-friendly but must be installed perfectly to perform well — gaps, compression, and misalignment dramatically reduce effectiveness. Mineral wool batts (Rockwool) cost more but offer better fire resistance, sound absorption, and moisture resistance.
Spray foam provides the highest R-value per inch and creates an air barrier simultaneously. Closed-cell (R-6.5/in) also serves as a vapor barrier and adds structural rigidity — ideal for basements and crawl spaces. Open-cell (R-3.7/in) is cheaper and better for sound absorption but doesn't block moisture. Spray foam requires professional installation.
Attic insulation has the fastest payback of any home improvement. Going from R-11 to R-49 in a 1,500 sq ft attic costs $750–$1,500 (DIY blown-in) and saves $200–$600 per year on energy bills — a 2–4 year payback. Wall insulation in existing homes (blown-in dense-pack) costs $1.50–$3.00/sq ft installed and pays back in 5–8 years. Spray foam is the most expensive but combines insulation, air sealing, and vapor barrier into one application.