Attic Insulation in Zone 4 (Mixed)
The DOE recommends R-49 for attic insulation in Climate Zone 4 (Mixed). This zone has 5,000 heating degree days and 1,200 cooling degree days annually. The typical attic cavity depth is 16 inches. States in Zone 4 include Arizona, Arkansas, California, Delaware, District of Columbia and 22 more.
Quick Facts
Insulation Comparison for Attic in Zone 4
The table below compares all insulation types for achieving R-49 in the attic of a building in Zone 4 (Mixed). Types marked "Recommended" are specifically suited for attic applications. Material costs are shown per square foot and per 1,000 square feet for easy budgeting. Labor costs typically add 30 to 100 percent to material costs depending on the insulation type and project complexity.
| Insulation Type | R/Inch | Thickness | $/SqFt | $/1000 SqFt | Fits | Rec. |
|---|---|---|---|---|---|---|
| Blown-In Cellulose | R-3.5 | 14" | $3.43 | $3,430 | Yes | Yes |
| Blown-In Fiberglass | R-2.5 | 19.6" | $3.92 | $3,920 | No | Yes |
| Vermiculite (Loose Fill) | R-2.1 | 23.3" | $4.90 | $4,900 | No | Yes |
| Fiberglass Batt | R-3.2 | 15.3" | $5.88 | $5,880 | Yes | Yes |
| Expanded Polystyrene (EPS) | R-3.9 | 12.6" | $5.88 | $5,880 | Yes | Yes |
| Mineral Wool Batt | R-3.3 | 14.8" | $7.35 | $7,350 | Yes | Yes |
| Cotton Denim (Recycled) | R-3.5 | 14" | $9.80 | $9,800 | Yes | Yes |
| Polyisocyanurate (Polyiso) | R-6 | 8.2" | $10.78 | $10,780 | Yes | Yes |
| Sheep Wool | R-3.5 | 14" | $17.15 | $17,150 | Yes | Yes |
| Extruded Polystyrene (XPS) | R-5 | 9.8" | $8.82 | $8,820 | Yes | - |
| Mineral Wool Board | R-4.3 | 11.4" | $12.25 | $12,250 | Yes | - |
| Open-Cell Spray Foam | R-3.7 | 13.2" | $19.60 | $19,600 | Yes | - |
| Closed-Cell Spray Foam | R-6.5 | 7.5" | $39.20 | $39,200 | Yes | - |
| Aerogel Blanket | R-10 | 4.9" | $147.00 | $147,000 | Yes | - |
Installation Guidance
Zone 4 requires a balanced attic insulation strategy that performs well in both heating and cooling seasons. The R-49 recommendation provides excellent year-round thermal performance. Blown-in cellulose or fiberglass is the most practical and cost-effective approach for achieving this R-value. Begin by air sealing all attic floor penetrations, then install ventilation baffles at the eaves. Blow insulation to a uniform depth across the entire attic floor, being careful to maintain full depth at the eaves where the roof slope reduces the available space. Mark the target insulation depth on several truss members or joist faces to guide the installation. If adding to existing insulation, do not compress the existing material — simply blow new insulation on top. The combined R-value of old and new insulation is approximately additive.
States in Zone 4
The following states include areas within Climate Zone 4. Click any state to see its complete insulation requirements across all applicable zones.