Spray Foam Cost Calculator

Open-Cell vs. Closed-Cell: The Cost-Performance Split

Spray foam insulation splits into two products that share a name but differ in nearly every measurable property. Choosing between them determines your project cost, required thickness, moisture management strategy, and long-term energy performance.

Closed-cell spray foam (ccSPF) delivers R-6.5 per inch at an installed density of about 2 lbs per cubic foot. It cures into a rigid, structural material that adds racking strength to walls — enough that some builders use it as a code-compliant alternative to plywood sheathing on timber-framed walls. The closed-cell structure makes it a Class II vapour retarder at 1.5 inches thick and a vapour barrier above 2 inches, meaning it controls moisture movement without a separate poly sheet. The trade-off is cost: closed-cell material runs $0.45-$0.65 per board foot before labour, and installation adds $0.50-$1.50 per board foot depending on access, thickness, and regional labour rates. As of March 2026, fully installed closed-cell foam costs $1.00-$2.15 per board foot across most US markets.

Open-cell spray foam (ocSPF) delivers R-3.7 per inch at 0.5 lbs per cubic foot — roughly half the R-value per inch and a quarter of the density. It cures into a soft, spongy material that excels at sound dampening but adds no structural value. Open-cell is vapour-permeable, which means walls can dry in both directions — an advantage in mixed climates where seasonal moisture drive reverses. Material cost is $0.15-$0.30 per board foot, and installed prices range $0.40-$1.00 per board foot. The catch is thickness: reaching R-38 in an attic requires over 10 inches of open-cell foam, which needs deep framing cavities or purpose-built channels.

Current blowing agents affect this comparison. Since 2021, most closed-cell foams in the US use HFO blowing agents (Honeywell Solstice or Chemours Opteon) with a global warming potential (GWP) under 1 — a massive improvement over the older HFC agents with GWPs above 1,000. This matters for green building certifications and for homeowners who weigh environmental impact alongside energy savings. Open-cell foams use water as the blowing agent and have always had negligible GWP. For a broader comparison that includes batts, blown-in, and mineral wool, the [insulation requirement calculator](/calculators/materials/insulation-requirement-calculator) helps match R-value targets to material thickness and cost across all common insulation types.

Calculating Board Feet and Installed Thickness

The unit of measure in spray foam pricing is the board foot — one square foot of coverage at one inch thick. A project that covers 1,000 sq ft at 3 inches thick uses 3,000 board feet of foam. Every quote you receive from a spray foam contractor should be in board feet, and understanding the math behind that number protects you from inflated bids.

1. **Determine your target R-value from your climate zone.** IECC 2021 Table R402.1.2 sets minimums by zone. Zone 3 walls need R-20 or R-13+5ci. Zone 5 walls need R-20+5ci or R-13+10ci. Attic floors range from R-30 (Zone 1-2) to R-60 (Zone 7-8). If you are building new or doing a full gut renovation, these are the minimums your inspector will check.

2. **Divide R-value by R per inch to get thickness.** Closed-cell at R-6.5/inch needs 3.23 inches for R-21. Open-cell at R-3.7/inch needs 5.68 inches for the same R-21. This thickness determines whether foam fits your framing — a 2x4 wall has 3.5 inches of cavity depth, so closed-cell works but open-cell falls short and would need a deeper wall.

3. **Multiply area by thickness to get raw board feet.** A 1,200 sq ft wall at 3.23 inches = 3,876 board feet. This is the theoretical minimum assuming perfect coverage and zero waste.

4. **Add your waste factor.** Flat, accessible walls with consistent cavity depth run 5-10% waste. Cathedral ceilings, irregular framing, and hard-to-reach areas push waste to 15-25%. Rim joists and band boards are among the worst for waste because the small, irregular surfaces mean more overspray relative to the area being covered.

5. **Price per board foot installed varies by region and thickness.** Most contractors quote installed price (material + labour combined) between $1.00 and $2.15 for closed-cell and $0.40 and $1.00 for open-cell. Thicker applications sometimes get volume discounts because the setup cost is the same regardless of how many passes the crew sprays. Get at least three quotes and make sure each one specifies board feet, foam brand, and blowing agent type.

Spray Foam Pricing by Application Zone

Project costs vary significantly by where the foam goes in the building. Access difficulty, required thickness, and substrate condition all affect the final per-board-foot price. Prices as of March 2026, US national averages from RS Means and contractor surveys.

| Application | Foam Type | Typical R-Value | Thickness | Cost/Sq Ft Installed | Notes | |---|---|---|---|---|---| | Exterior walls (2x4 cavity) | Closed-cell | R-13 to R-21 | 2-3.2 in | $3.00-$6.50 | Most common residential application | | Exterior walls (2x6 cavity) | Closed-cell | R-21 to R-33 | 3.2-5 in | $4.50-$10.00 | Full cavity fill or flash-and-batt | | Exterior walls (2x6 cavity) | Open-cell | R-13 to R-21 | 3.5-5.5 in | $1.75-$5.00 | Full cavity fill, needs separate vapour strategy in cold climates | | Attic floor | Open-cell | R-38 to R-49 | 10-13 in | $5.00-$10.00 | High volume, open access = lower per-bd-ft labour | | Cathedral ceiling / roofline | Closed-cell | R-30 to R-49 | 4.6-7.5 in | $7.00-$15.00 | Overhead work, multiple passes, higher waste | | Crawl space walls | Closed-cell | R-10 to R-15 | 1.5-2.3 in | $2.50-$5.00 | Confined space increases labour rate | | Rim joists / band boards | Closed-cell | R-13 to R-21 | 2-3 in | $4.00-$7.00 | Small areas, high per-unit labour | | Metal building | Closed-cell | R-19 to R-25 | 3-4 in | $3.50-$7.50 | Direct-to-steel, large open areas |

Flash-and-batt is a common hybrid approach: 1-2 inches of closed-cell foam sprayed against the sheathing provides the air seal and vapour control, then the remaining cavity is filled with fiberglass batts. This combines the air-sealing performance of spray foam with the lower cost of batts. A 2x6 wall with 2 inches of closed-cell (R-13) plus R-15 batts achieves R-28 at roughly 60% of the cost of filling the entire cavity with closed-cell. Homeowners considering this approach alongside other thermal envelope options can compare total project costs with the [insulation requirement calculator](/calculators/materials/insulation-requirement-calculator).

Hidden Costs and Contractor Red Flags

The board-foot price in a spray foam quote does not capture the full project cost. Several line items consistently surprise homeowners who compare quotes only on the per-board-foot number.

**Thermal barrier coverage.** Building code (IRC R316.4) requires a 15-minute thermal barrier over spray foam in habitable spaces. Half-inch drywall satisfies this requirement and is the standard approach in walls and ceilings. But in unfinished basements, crawl spaces, and attics, the foam may be left exposed — and if it is, you need an intumescent coating ($1.50-$3.00 per sq ft) or an ignition barrier ($0.50-$1.00 per sq ft for thin plywood or sheathing). Some codes allow the foam itself to qualify if it passes specific fire tests, but this depends on the product and jurisdiction. Ask your contractor what their quote includes for thermal barrier compliance.

**Trimming and cleanup.** Spray foam expands beyond the cavity surface and must be trimmed flush before drywall can be installed. Some contractors include trimming in their price; others charge $0.10-$0.25 per sq ft extra. On a 1,200 sq ft wall job, that is $120-$300 of unexpected cost. Overspray on windows, electrical boxes, and framing surfaces needs scraping or solvent removal — again, sometimes included, sometimes not.

**Electrical and plumbing coordination.** Spray foam locks around wires and pipes, making future modifications difficult. All electrical, plumbing, and HVAC rough-in must be complete and inspected before foam goes in. If your project timeline slips and the foam crew arrives before the electrician finishes, you either delay the foam (losing your scheduled slot) or foam around incomplete work and pay an electrician premium to fish wires through cured foam later.

**Contractor red flags to watch for.** Spray foam is a specialised trade with real risks when done poorly. Avoid contractors who: cannot name the specific foam product and blowing agent they use; quote by square foot instead of board feet (this hides the actual thickness they plan to spray); will not provide a copy of their SPFA certification; skip the 24-hour re-entry period after spraying (off-ratio foam emits isocyanate vapour that causes respiratory sensitisation); or refuse to leave the manufacturer's batch sticker on site. A waterproofing project below grade often pairs with spray foam work — the [waterproofing membrane calculator](/calculators/materials/waterproofing-membrane-calculator) estimates membrane and drainage board quantities for foundation walls.

When Spray Foam Is Not Worth It

Spray foam is the highest-performing insulation option in most applications, but it is not always the most cost-effective choice. Several scenarios favour cheaper alternatives.

**Standard attic floors with accessible joists.** Blown-in cellulose or fiberglass achieves R-38 to R-60 at $1.50-$3.00 per sq ft installed — roughly half to a third of open-cell spray foam. The attic floor is one of the few locations where air sealing can be achieved separately (caulk and canned foam around penetrations) before blowing insulation on top. Unless you need a conditioned attic for ductwork or storage, blown-in wins on cost per R-value.

**Walls with intact air barriers.** If your wall assembly already has a good air barrier (taped ZIP sheathing, sealed housewrap, or existing spray foam), adding fiberglass batts or mineral wool to the cavity provides the same R-value at a fraction of the cost. Spray foam's main advantage in walls is air sealing, not R-value — if the air barrier problem is already solved, you are paying a premium for a benefit you already have.

**Gut renovations where you control the assembly.** When you are framing new walls, you can design the air barrier into the sheathing system and use cheaper cavity insulation. Flash-and-batt (1-2 inches of closed-cell plus batts) gives you the air seal at the sheathing plane and fills the cavity inexpensively. A full cavity of closed-cell in a 2x6 wall costs $7-$15 per sq ft installed; flash-and-batt achieves 80% of the performance for 50% of the cost.

**Small, accessible projects.** Spray foam contractors typically have minimum job charges of $1,500-$3,000 because the equipment setup, mixing, and cleanup time is the same regardless of project size. If you need to insulate 100 sq ft of rim joist, the per-board-foot price will be high because the overhead is spread across fewer units. For small jobs, rigid foam board (XPS or polyiso) cut and sealed with canned foam is the more economical approach.

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