Cathedral Ceiling Insulation in Zone 2 (Hot)
The DOE recommends R-22 for cathedral ceiling insulation in Climate Zone 2 (Hot). This zone has 2,000 heating degree days and 3,500 cooling degree days annually. The typical cathedral ceiling cavity depth is 9.25 inches. States in Zone 2 include Alabama, Arizona, Florida, Georgia, Louisiana and 2 more.
Quick Facts
Insulation Comparison for Cathedral Ceiling in Zone 2
The table below compares all insulation types for achieving R-22 in the cathedral ceiling of a building in Zone 2 (Hot). Types marked "Recommended" are specifically suited for cathedral ceiling 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. |
|---|---|---|---|---|---|---|
| Polyisocyanurate (Polyiso) | R-6 | 3.7" | $4.84 | $4,840 | Yes | Yes |
| Open-Cell Spray Foam | R-3.7 | 5.9" | $8.80 | $8,800 | Yes | Yes |
| Closed-Cell Spray Foam | R-6.5 | 3.4" | $17.60 | $17,600 | Yes | Yes |
| Blown-In Cellulose | R-3.5 | 6.3" | $1.54 | $1,540 | Yes | - |
| Blown-In Fiberglass | R-2.5 | 8.8" | $1.76 | $1,760 | Yes | - |
| Vermiculite (Loose Fill) | R-2.1 | 10.5" | $2.20 | $2,200 | No | - |
| Fiberglass Batt | R-3.2 | 6.9" | $2.64 | $2,640 | Yes | - |
| Expanded Polystyrene (EPS) | R-3.9 | 5.6" | $2.64 | $2,640 | Yes | - |
| Mineral Wool Batt | R-3.3 | 6.7" | $3.30 | $3,300 | Yes | - |
| Extruded Polystyrene (XPS) | R-5 | 4.4" | $3.96 | $3,960 | Yes | - |
| Cotton Denim (Recycled) | R-3.5 | 6.3" | $4.40 | $4,400 | Yes | - |
| Mineral Wool Board | R-4.3 | 5.1" | $5.50 | $5,500 | Yes | - |
| Sheep Wool | R-3.5 | 6.3" | $7.70 | $7,700 | Yes | - |
| Aerogel Blanket | R-10 | 2.2" | $66.00 | $66,000 | Yes | - |
Installation Guidance
Cathedral ceiling insulation at R-22 in Zone 2 requires careful planning because the available depth is limited by the rafter size. Standard rafter cavities can accommodate R-22 with careful material selection. Dense-pack cellulose or closed-cell spray foam in the rafter cavity is effective. For vented cathedral ceiling assemblies, maintain at least a 1-inch continuous air space between the insulation and the roof sheathing by installing rigid ventilation baffles in every rafter bay. This ventilation channel runs from the soffit to the ridge, allowing moisture to escape and preventing ice dam formation in cold climates. For unvented assemblies, the IRC requires that either the entire R-value be provided by air-impermeable insulation (spray foam), or a specific ratio of air-impermeable to air-permeable insulation be maintained to prevent condensation on the roof sheathing.
States in Zone 2
The following states include areas within Climate Zone 2. Click any state to see its complete insulation requirements across all applicable zones.