What Is Closed Cell Spray Foam?
Closed cell spray foam is a dense, rigid insulation that cures into a solid, impermeable layer. Unlike open cell foam, its individual cells are closed — meaning they're filled with a blowing agent that doesn't dissipate, giving closed cell foam its industry-leading R-value of R-6.0 to R-6.5 per inch.
When you apply 3.5 inches of closed cell foam to a wall cavity, you achieve an effective R-value of approximately R-22 — exceeding current energy code requirements for most Utah applications in a single product, with zero air infiltration and a built-in vapor barrier.
Why Closed Cell Is the Right Choice for Most St. George Applications
Southern Utah's climate creates specific insulation demands that make closed cell spray foam the clear winner for several applications:
Attic & Roof Deck
St. George attics can reach 150°F+ on a summer afternoon. Spraying closed cell foam directly to the underside of the roof deck transforms your attic from an oven to a conditioned space — dramatically reducing your HVAC load and making HVAC equipment in the attic last years longer.
Metal Buildings & Shops
Metal is one of the worst thermal conductors — bare metal buildings in the St. George summer are nearly unusable without insulation. Closed cell foam applied to the walls and ceiling of a metal structure creates a thermal and moisture barrier that makes commercial and agricultural buildings comfortable year-round.
Crawl Spaces & Below-Grade
Washington County's monsoon season introduces moisture that traditional insulation absorbs and retains. Closed cell foam's impermeability makes it ideal for crawl spaces, basement walls, and any below-grade application where moisture intrusion is a risk.
Rim Joists & Foundations
The rim joist (where the floor framing meets the foundation wall) is one of the most air-leaky areas in a home. Closed cell foam applied to the rim joist seals air infiltration, insulates against the desert heat transfer, and adds structural rigidity.
Closed Cell Foam R-Value: What the Numbers Mean
R-value measures thermal resistance — the higher, the better. Here's how closed cell foam compares to common alternatives:
| Insulation Type | R-Value per Inch | Air Sealing | Vapor Barrier |
|---|---|---|---|
| Closed Cell Spray Foam | R-6.0 – R-6.5 | ✅ Excellent | ✅ Yes |
| Open Cell Spray Foam | R-3.5 – R-3.7 | ✅ Good | ❌ No |
| Fiberglass Batt | R-2.9 – R-3.8 | ❌ Poor | ❌ No |
| Blown-In Cellulose | R-3.2 – R-3.8 | ❌ Poor | ❌ No |
| Rigid Foam Board | R-3.8 – R-6.5 | ⚠️ Seams only | ⚠️ Partial |
Closed Cell Spray Foam Cost in St. George, UT
Closed cell spray foam typically costs $1.00–$1.50 per board foot installed in the St. George area. For reference, one board foot covers one square foot at one inch of thickness.
Common project cost ranges:
- 2,000 sq. ft. attic (roof deck spray, 3" thickness): $3,000 – $5,500
- Metal building walls + ceiling (2,400 sq. ft., 2" thickness): $3,500 – $6,000
- Crawl space walls + rim joist (1,200 sq. ft. home): $1,200 – $2,500
- Full exterior wall spray, new construction (2,000 sq. ft.): $4,000 – $7,000
These are ranges — actual pricing depends on current material costs, access conditions, and project specifics. A free on-site estimate gives you an exact number.
The Structural Benefit: A Hidden Advantage
An often-overlooked benefit of closed cell spray foam is structural reinforcement. When applied to wall sheathing and roof decking, closed cell foam bonds rigidly to the surface and increases the racking strength of the structure. In Southern Utah's occasional high-wind events, this added rigidity can make a real difference.
Studies have shown that closed cell foam applied to roof decking can increase uplift resistance by up to 75% compared to uninsulated structures — a meaningful benefit for homes and commercial buildings in Washington County.
What About Energy Code Compliance?
Utah follows the International Energy Conservation Code (IECC). For Climate Zone 3B (where St. George is located), the code requirements for wall insulation are R-15 or R-13+5 continuous. Closed cell spray foam at 2.5 inches in a 2×4 wall achieves approximately R-16.5 — meeting code in a single application with no additional continuous insulation required.
We'll help ensure your project is code-compliant from the start. Our crew is familiar with Washington County building permit requirements and common inspection standards.
Service Areas
We install closed cell spray foam throughout Washington County including: St. George, Washington, Hurricane, Santa Clara, Ivins, La Verkin, Toquerville, Leeds, Springdale, and Rockville. We also serve Cedar City and Enoch in Iron County.