Wall Cavity Insulation in Zone 8 (Subarctic)
The DOE recommends R-13 for wall cavity insulation in Climate Zone 8 (Subarctic). This zone has 14,000 heating degree days and 100 cooling degree days annually. The typical wall cavity cavity depth is 3.5 inches. States in Zone 8 include Alaska.
Quick Facts
Insulation Comparison for Wall Cavity in Zone 8
The table below compares all insulation types for achieving R-13 in the wall cavity of a building in Zone 8 (Subarctic). Types marked "Recommended" are specifically suited for wall cavity 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 | 3.7" | $0.91 | $910 | No | Yes |
| Blown-In Fiberglass | R-2.5 | 5.2" | $1.04 | $1,040 | No | Yes |
| Fiberglass Batt | R-3.2 | 4.1" | $1.56 | $1,560 | No | Yes |
| Mineral Wool Batt | R-3.3 | 3.9" | $1.95 | $1,950 | No | Yes |
| Cotton Denim (Recycled) | R-3.5 | 3.7" | $2.60 | $2,600 | No | Yes |
| Sheep Wool | R-3.5 | 3.7" | $4.55 | $4,550 | No | Yes |
| Open-Cell Spray Foam | R-3.7 | 3.5" | $5.20 | $5,200 | No | Yes |
| Closed-Cell Spray Foam | R-6.5 | 2" | $10.40 | $10,400 | Yes | Yes |
| Aerogel Blanket | R-10 | 1.3" | $39.00 | $39,000 | Yes | Yes |
| Vermiculite (Loose Fill) | R-2.1 | 6.2" | $1.30 | $1,300 | No | - |
| Expanded Polystyrene (EPS) | R-3.9 | 3.3" | $1.56 | $1,560 | Yes | - |
| Extruded Polystyrene (XPS) | R-5 | 2.6" | $2.34 | $2,340 | Yes | - |
| Polyisocyanurate (Polyiso) | R-6 | 2.2" | $2.86 | $2,860 | Yes | - |
| Mineral Wool Board | R-4.3 | 3" | $3.25 | $3,250 | Yes | - |
Installation Guidance
Wall cavity insulation in Zone 8 should achieve at least R-13 within the stud cavity. For 2x4 framing, R-13 or R-15 fiberglass or mineral wool batts fill the 3.5-inch cavity. For 2x6 framing, R-20 or R-21 batts provide significantly better performance. In cold climates, the quality of batt installation is critical because even small gaps allow convection currents that can reduce the effective R-value by 30 percent or more. Specify Grade I installation per RESNET standards, which requires complete cavity fill with no visible gaps when viewed from the face. Dense-pack cellulose or fiberglass is an excellent alternative for both new construction and retrofits, providing inherently better air sealing than batts. Remember that in Zone 8, continuous exterior insulation is also recommended in addition to cavity insulation to address thermal bridging through the studs.
States in Zone 8
The following states include areas within Climate Zone 8. Click any state to see its complete insulation requirements across all applicable zones.