Zone 4 Wall Continuous (Exterior) Insulation — R-5
The DOE recommends R-5 insulation for the wall continuous (exterior) in Climate Zone 4 (Mixed). The typical wall continuous (exterior) cavity depth is 2 inches. This page compares all insulation types showing the thickness needed, material cost per square foot, and whether each type fits within the standard cavity depth.
Quick Summary
Insulation Type Comparison for Zone 4 Wall Continuous (Exterior)
The following table compares all insulation types for achieving R-5 in the wall continuous (exterior) of a building in Climate Zone 4. Types marked as "recommended" are specifically suited for this building component. The cost estimates represent material costs only and do not include labor, which can add 30-100% depending on the insulation type and project complexity.
| Insulation Type | R/Inch | Thickness | Cost/SqFt | Cost/1000 SqFt | Fits Cavity | Recommended |
|---|---|---|---|---|---|---|
| Expanded Polystyrene (EPS) | R-3.9 | 1.3" | $0.60 | $600 | Yes | Yes |
| Extruded Polystyrene (XPS) | R-5 | 1" | $0.90 | $900 | Yes | Yes |
| Polyisocyanurate (Polyiso) | R-6 | 0.8" | $1.10 | $1,100 | Yes | Yes |
| Mineral Wool Board | R-4.3 | 1.2" | $1.25 | $1,250 | Yes | Yes |
| Aerogel Blanket | R-10 | 0.5" | $15.00 | $15,000 | 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 | No | - |
| Fiberglass Batt | R-3.2 | 1.6" | $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 | - |
| 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 | - |
| Closed-Cell Spray Foam | R-6.5 | 0.8" | $4.00 | $4,000 | Yes | - |
Installation Guidance
Continuous exterior wall insulation at R-5 in Zone 4 addresses the significant thermal bridging that occurs through wood framing members in conventional wall construction. Wood studs at 16 inches on center occupy approximately 25 percent of the wall area and conduct heat 3 to 4 times faster than insulation, reducing the effective whole-wall R-value by 15 to 25 percent. Adding R-5 of continuous insulation on the exterior eliminates this thermal bridging and also keeps the wall sheathing warmer, reducing the risk of condensation within the wall cavity. Common materials include rigid foam boards (XPS at R-5 per inch, polyiso at R-6 per inch) and mineral wool boards (R-4.3 per inch). The insulation is installed over the wall sheathing with mechanical fasteners, and exterior cladding is then attached through the insulation using furring strips or long screws. This approach is particularly effective during re-siding projects on existing homes.
Construction Notes
Continuous exterior insulation is installed on the outside of wall sheathing, creating an unbroken thermal layer that eliminates thermal bridging through framing members. Thermal bridging through wood studs can reduce the effective whole-wall R-value by 15-25 percent compared to the clear-cavity R-value. Common materials for continuous insulation include rigid foam boards (XPS, EPS, polyiso) and mineral wool boards. The insulation is typically attached with adhesive and mechanical fasteners, and exterior cladding is then installed over furring strips. Adding continuous insulation to existing homes during re-siding projects is one of the most effective energy upgrades available.