Zone 8 Crawlspace Insulation — R-10
The DOE recommends R-10 insulation for the crawlspace in Climate Zone 8 (Subarctic). The typical crawlspace cavity depth is 4 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 8 Crawlspace
The following table compares all insulation types for achieving R-10 in the crawlspace of a building in Climate Zone 8. 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 |
|---|---|---|---|---|---|---|
| Extruded Polystyrene (XPS) | R-5 | 2" | $1.80 | $1,800 | Yes | Yes |
| Open-Cell Spray Foam | R-3.7 | 2.7" | $4.00 | $4,000 | Yes | Yes |
| Closed-Cell Spray Foam | R-6.5 | 1.5" | $8.00 | $8,000 | Yes | Yes |
| Blown-In Cellulose | R-3.5 | 2.9" | $0.70 | $700 | Yes | - |
| Blown-In Fiberglass | R-2.5 | 4" | $0.80 | $800 | Yes | - |
| Vermiculite (Loose Fill) | R-2.1 | 4.8" | $1.00 | $1,000 | No | - |
| Fiberglass Batt | R-3.2 | 3.1" | $1.20 | $1,200 | Yes | - |
| Expanded Polystyrene (EPS) | R-3.9 | 2.6" | $1.20 | $1,200 | Yes | - |
| Mineral Wool Batt | R-3.3 | 3" | $1.50 | $1,500 | Yes | - |
| Cotton Denim (Recycled) | R-3.5 | 2.9" | $2.00 | $2,000 | Yes | - |
| Polyisocyanurate (Polyiso) | R-6 | 1.7" | $2.20 | $2,200 | Yes | - |
| Mineral Wool Board | R-4.3 | 2.3" | $2.50 | $2,500 | Yes | - |
| Sheep Wool | R-3.5 | 2.9" | $3.50 | $3,500 | Yes | - |
| Aerogel Blanket | R-10 | 1" | $30.00 | $30,000 | Yes | - |
Installation Guidance
Crawlspace insulation at R-10 in Zone 8 depends on whether the crawlspace is vented or unvented. In a vented crawlspace, insulation is installed in the floor above (between joists) rather than on the crawlspace walls, using the same approach as floor insulation. In an unvented (conditioned) crawlspace, insulation is applied to the crawlspace walls using rigid foam or closed-cell spray foam, and the space is sealed and sometimes mechanically conditioned. The unvented approach is generally more energy-efficient because it brings the crawlspace inside the thermal envelope, reducing heat loss through floor penetrations and ductwork. The DOE and building science community increasingly recommend unvented crawlspaces in all climate zones. Wall insulation in an unvented crawlspace must extend from the top of the wall to the footing, and a minimum 6-mil polyethylene vapor barrier must cover the ground floor with seams overlapped and sealed.
Construction Notes
Crawlspace insulation approaches depend on whether the crawlspace is vented or unvented (conditioned). In a vented crawlspace, insulation is installed in the floor above between the joists, similar to floor insulation. In an unvented crawlspace, insulation is applied to the crawlspace walls instead of the floor, and the crawlspace is sealed and sometimes conditioned. The unvented approach is generally more energy-efficient and eliminates moisture problems associated with vented crawlspaces in humid climates. Wall insulation in an unvented crawlspace should be moisture-resistant (rigid foam or closed-cell spray foam) and must extend from the top of the wall to the footing. A vapor barrier on the ground floor is essential in both vented and unvented crawlspaces.