By Insulation Service LLC | Updated 2026
Spray foam insulation costs more than fiberglass or cellulose upfront, but it delivers two things those materials cannot: air sealing and moisture control in a single application. The question is not whether spray foam is worth it. The question is how much it costs for your specific project. This guide breaks down spray foam pricing by foam type, by application, and by real project scenarios in central Illinois.
$0.35 – $0.55
per board foot installed
$1.00 – $1.50
per board foot installed
A board foot is one square foot of coverage at one inch of thickness. To convert board-foot pricing to per-square-foot cost, multiply the board-foot price by the number of inches being applied. For example, 3.5 inches of open-cell foam at $0.45 per board foot equals approximately $1.58 per square foot. These are installed costs including material, labor, and equipment for professional installation in central Illinois.
| Factor | Open-Cell | Closed-Cell |
|---|---|---|
| Cost Per Board Foot | $0.35 – $0.55 | $1.00 – $1.50 |
| R-Value Per Inch | R-3.5 to R-4.0 | R-6.0 to R-7.0 |
| Air Barrier | Yes | Yes |
| Vapor Retarder | No | Yes (at 2"+) |
| Moisture Resistance | Absorbs water; not for wet areas | Blocks moisture; suitable for crawl spaces |
| Structural Benefit | Minimal | Adds rigidity to framing |
| Best Applications | Attic rooflines, interior walls, soundproofing | Crawl spaces, rim joists, metal buildings, basements |
Open-cell foam costs roughly one-third of what closed-cell foam costs per board foot. But because open-cell provides roughly half the R-value per inch, you need nearly twice the thickness to achieve the same thermal resistance. The real cost difference is in what each product delivers beyond R-value. We install both types and recommend the right one for each application. Learn more about open-cell vs. closed-cell spray foam →
Spraying the underside of the roof deck converts the attic to conditioned space. The right approach when HVAC equipment or ductwork is in the attic.
| Project | Foam Type | Thickness | Approx. Cost |
|---|---|---|---|
| 1,000 sq ft attic roofline | Open-cell | 5.5" (R-20) | $1,900 – $3,000 |
| 1,500 sq ft attic roofline | Open-cell | 5.5" (R-20) | $2,900 – $4,500 |
| 1,000 sq ft attic roofline | Closed-cell | 3" (R-20) | $3,000 – $4,500 |
| 1,500 sq ft attic roofline | Closed-cell | 3" (R-20) | $4,500 – $6,750 |
Note: For most homes with standard unconditioned attics, blown-in cellulose on the attic floor is more cost-effective at $1.50–$3.00/sq ft. Learn more about attic insulation →
Closed-cell spray foam on foundation walls as part of an encapsulation system.
| Project | Foam Type | Thickness | Approx. Cost |
|---|---|---|---|
| 500 sq ft of wall | Closed-cell | 2" (R-13) | $1,500 – $2,500 |
| 1,000 sq ft of wall | Closed-cell | 2" (R-13) | $3,000 – $5,000 |
| Full encapsulation (1,000 sq ft floor + all work) | Closed-cell | 2" | $5,000 – $12,000 |
Full encapsulation includes vapor barrier, wall insulation, rim joist foam, vent sealing, and cleanup. Learn more about crawl space insulation →
Two inches of closed-cell spray foam on each rim joist cavity. One of the highest-ROI spray foam applications.
| Project | Foam Type | Thickness | Approx. Cost |
|---|---|---|---|
| Typical ranch home (120 linear ft) | Closed-cell | 2" (R-13) | $600 – $1,200 |
| Typical two-story home (180 linear ft) | Closed-cell | 2" (R-13) | $900 – $1,800 |
Closed-cell spray foam on the interior of metal roof and wall panels.
| Project | Thickness | Approx. Cost |
|---|---|---|
| 30x40 pole barn, roof only | 2" (R-13) | $3,600 – $5,400 |
| 30x40 pole barn, roof + walls | 2" (R-13) | $6,000 – $9,000 |
| 40x60 pole barn, roof only | 2" (R-13) | $5,800 – $8,600 |
| 40x60 pole barn, roof + walls | 2" (R-13) | $9,500 – $14,500 |
| 40x60 heated shop, roof + walls | 3" (R-20) | $14,000 – $21,000 |
Roof-only is most common for unheated storage. Add wall insulation for heated shops. Pole Barn Insulation → | Metal Building Insulation →
The single biggest cost variable. Closed-cell costs roughly 3x more per board foot. The right choice depends on the application, not the budget.
More inches equals more material. A 2" closed-cell application costs roughly half what a 4" application costs on the same surface.
Larger projects have lower cost per square foot because crew and equipment setup is the same regardless of project size.
Tight crawl spaces, steep attic slopes, and high ceilings all increase labor time. Open pole barns are faster and cheaper per sq ft.
Removal of old batts adds $1.00–$2.00/sq ft. Necessary when material is wet, moldy, or would create an air gap behind new foam.
New construction is less expensive—open walls, no belongings to protect. Existing home retrofits cost 15–20% more on average.
Central Illinois labor rates are lower than Chicago, St. Louis, or Indianapolis. Our pricing reflects central Illinois installed costs—not national averages.
Most central Illinois homes benefit from spray foam in specific, targeted locations (rim joists, crawl spaces) combined with less expensive insulation in bulk areas (blown-in cellulose in attic, fiberglass in new construction walls). We design projects this way because it gives customers the best performance per dollar spent. Learn more about our spray foam services →
| Insulation Type | Cost/Sq Ft | R-Value/Inch | Air Sealing | Best For |
|---|---|---|---|---|
| Open-Cell Spray Foam | $1.50–$3.50 | R-3.5–R-4.0 | Attic rooflines, interior walls | |
| Closed-Cell Spray Foam | $2.50–$5.00 | R-6.0–R-7.0 | Crawl spaces, rim joists, metal buildings | |
| Blown-In Cellulose | $1.00–$2.00 | R-3.2–R-3.8 | Moderate | Attic floors, wall retrofits |
| Blown-In Fiberglass | $1.00–$1.75 | R-2.2–R-2.7 | Attic floors | |
| Fiberglass Batts | $0.80–$2.00 | R-3.1–R-3.8 | New construction walls |
The ranges in this guide give you a starting point, but your actual cost depends on your specific building, the areas being sprayed, and the foam type required. We provide free, detailed estimates with exact pricing. No guesswork. No national averages. Just what your project will cost in central Illinois.