Closed-Cell Spray Foam in Zone 8 (Subarctic)
Closed-Cell Spray Foam provides R-6.5 per inch of thickness at a material cost of $0.80 per square foot per R-value point. In Climate Zone 8 (Subarctic), with 14,000 HDD and 100 CDD, see the thickness and cost required for each building component below.
Specifications
Closed-Cell Spray Foam Requirements by Component in Zone 8
The table below shows the DOE recommended R-value, required thickness of Closed-Cell Spray Foam, material cost per square foot, and total material cost per 1,000 square feet for each building component in Climate Zone 8. Components where Closed-Cell Spray Foam is specifically recommended are highlighted. Components where insulation is not required show "N/R" (not required).
| Component | Required R | Thickness | $/SqFt | $/1000 SqFt | Fits Cavity | Rec. |
|---|---|---|---|---|---|---|
| Attic | R-60 | 9.2" | $48.00 | $48,000 | Yes | - |
| Wall Cavity | R-13 | 2" | $10.40 | $10,400 | Yes | Yes |
| Wall Continuous (Exterior) | R-15 | 2.3" | $12.00 | $12,000 | No | - |
| Floor (Over Unconditioned Space) | R-25 | 3.8" | $20.00 | $20,000 | Yes | - |
| Basement Wall | R-19 | 2.9" | $15.20 | $15,200 | Yes | Yes |
| Crawlspace | R-10 | 1.5" | $8.00 | $8,000 | Yes | Yes |
| Cathedral Ceiling | R-49 | 7.5" | $39.20 | $39,200 | Yes | Yes |
| Garage Ceiling (Below Living Space) | R-38 | 5.8" | $30.40 | $30,400 | Yes | - |
Closed-Cell Spray Foam in Zone 8 — Guidance
Closed-cell spray foam at R-6.5 per inch is particularly valuable in Zone 8 (Subarctic) where its high R-value per inch allows maximum thermal performance in limited cavity depths. The rigid, closed-cell structure provides a continuous air barrier and Class II vapor retarder at 2 inches or more of thickness, addressing two of the most critical building science concerns in cold climates. At rim joists, closed-cell spray foam is the gold standard — 2 to 3 inches provides R-13 to R-19.5 while sealing the notoriously leaky rim joist area. For basement walls, spray foam applied directly to concrete eliminates the condensation risk associated with fiberglass and provides insulation, air sealing, and moisture control in a single application. The high cost of closed-cell foam is most justified in Zone 8 where the energy savings from its superior thermal performance and air sealing provide the fastest payback.
States in Zone 8
These states include areas within Climate Zone 8 where the Closed-Cell Spray Foam requirements shown above apply. Click any state for its complete insulation recommendations.