Basement Wall Insulation in Zone 3 (Warm)
The DOE recommends R-5 for basement wall insulation in Climate Zone 3 (Warm). This zone has 3,500 heating degree days and 2,000 cooling degree days annually. The typical basement wall cavity depth is 4 inches. States in Zone 3 include Alabama, Arizona, Arkansas, California, Georgia and 10 more.
Quick Facts
Insulation Comparison for Basement Wall in Zone 3
The table below compares all insulation types for achieving R-5 in the basement wall of a building in Zone 3 (Warm). Types marked "Recommended" are specifically suited for basement wall 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. |
|---|---|---|---|---|---|---|
| Extruded Polystyrene (XPS) | R-5 | 1" | $0.90 | $900 | Yes | Yes |
| Mineral Wool Board | R-4.3 | 1.2" | $1.25 | $1,250 | Yes | Yes |
| Closed-Cell Spray Foam | R-6.5 | 0.8" | $4.00 | $4,000 | Yes | Yes |
| Blown-In Cellulose | R-3.5 | 1.4" | $0.35 | $350 | Yes | - |
| Blown-In Fiberglass | R-2.5 | 2" | $0.40 | $400 | Yes | - |
| Vermiculite (Loose Fill) | R-2.1 | 2.4" | $0.50 | $500 | Yes | - |
| Fiberglass Batt | R-3.2 | 1.6" | $0.60 | $600 | Yes | - |
| Expanded Polystyrene (EPS) | R-3.9 | 1.3" | $0.60 | $600 | Yes | - |
| Mineral Wool Batt | R-3.3 | 1.5" | $0.75 | $750 | Yes | - |
| Cotton Denim (Recycled) | R-3.5 | 1.4" | $1.00 | $1,000 | Yes | - |
| Polyisocyanurate (Polyiso) | R-6 | 0.8" | $1.10 | $1,100 | Yes | - |
| Sheep Wool | R-3.5 | 1.4" | $1.75 | $1,750 | Yes | - |
| Open-Cell Spray Foam | R-3.7 | 1.4" | $2.00 | $2,000 | Yes | - |
| Aerogel Blanket | R-10 | 0.5" | $15.00 | $15,000 | Yes | - |
Installation Guidance
Basement wall insulation at R-5 in Zone 3 is best achieved with moisture-resistant materials installed against the concrete foundation. The preferred approach for existing basements is to apply 1.5 to 2 inches of rigid XPS or polyiso directly to the concrete wall using compatible adhesive, then build a 2x4 framed wall in front of the foam for electrical runs and drywall attachment. The framed cavity can be left empty (the rigid foam alone may provide sufficient R-value) or filled with unfaced fiberglass batts for additional thermal performance. Closed-cell spray foam applied directly to the concrete is an excellent alternative that provides insulation, air sealing, and moisture barrier in a single application. Never use fiberglass batts against bare concrete — moisture will condense on the cold concrete, saturate the fiberglass, and create conditions for mold growth. Ensure that the top of the foundation wall (the sill plate area) is also insulated and air sealed, as this is one of the most significant air leakage points in most basements.
States in Zone 3
The following states include areas within Climate Zone 3. Click any state to see its complete insulation requirements across all applicable zones.