Which spray foam is cheaper in Knoxville, open cell or closed cell?

Open cell is cheaper per square foot ($1.50 to $3.50 in Knoxville) than closed cell ($3.00 to $5.00). Open cell is the typical choice for Knoxville attics and interior walls. Closed cell costs more but offers roughly 2x the R-value per inch and acts as a vapor barrier, making it the right choice for crawl spaces, rim joists and metal buildings.

How much does an attic spray foam job cost in Knoxville?

A typical Knoxville attic spray foam job costs $3,000 to $7,500 for a 1,500 to 2,500 square foot home. Open cell at code-recommended R-49 runs roughly $2.50 per square foot installed. Removing existing fiberglass batt before spraying adds $0.50 to $1.00 per square foot.

Spray Foam Insulation Cost in Knoxville, Tennessee

Q: How much does spray foam insulation cost in Knoxville TN?

Spray foam insulation in Knoxville typically costs $1.50 to $5.00 per square foot installed. Open cell averages $1.50 to $3.50 per square foot and closed cell averages $3.00 to $5.00 per square foot. A typical 1,500 square foot Knoxville home runs $3,000 to $7,500 total.

Typical local market ranges for 2026.

Spray foam insulation cost breakdown for a Knoxville, Tennessee home

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How much does spray foam insulation cost in Knoxville?

Spray foam insulation in Knoxville costs $1.50 to $5.00 per square foot installed. Open cell runs $1.50 to $3.50 per square foot. Closed cell runs $3.00 to $5.00 per square foot. These are typical Knoxville market ranges in 2026, not a fixed price list - the actual number for your home depends on foam type, access, and prep. Ask any Knoxville spray foam installer for a written quote before work starts.

Typical Knoxville Spray Foam Market Prices

The ranges below are typical local market prices across Knoxville and East Tennessee in 2026, drawn from the 2026 Knoxville cost guide. They are not a fixed price list and every quote should be in writing before work starts.

Open cell spray foam: $1.50 to $3.50 per sq ft installed. R-3.5 per inch. Best for Knoxville attics and interior walls. See the open cell page.
Closed cell spray foam: $3.00 to $5.00 per sq ft installed. R-7 per inch, vapor barrier. Best for crawl spaces, rim joists, below-grade walls and metal buildings. See the closed cell page.
Attic spray foam retrofit: $3,000 to $7,500 for a typical 1,500 to 2,500 sq ft Knoxville home. See the attic page.
Crawl space encapsulation: $1,500 to $4,500 for a typical home. See the crawl space page.
Rim joist spray foam: $800 to $2,500 for a whole-house perimeter. See the rim joist page.
Metal building spray foam: $2.50 to $6.00 per sq ft of panel area for Knoxville steel buildings. See the metal building page.
Pole barn / barndominium: $7,500 to $14,000 for a typical 30x40 Knoxville pole barn with closed cell on roof and walls. See the pole barn page.
Spray foam removal: $2.00 to $8.00 per sq ft depending on access, foam type and substrate. See the removal page.
Fiberglass batt removal before spraying: adds $0.50 to $1.00 per sq ft to a Knoxville attic or crawl space job.

Open Cell vs Closed Cell: Price and Performance in Knoxville

The two spray foam types used in Knoxville homes are open cell and closed cell. They are not interchangeable - each has an application where it is the right call and a price point to match.

Open cell - $1.50 to $3.50 per sq ft, R-3.5 per inch, vapor-permeable, soft and expansive. Default for Knoxville attics and interior walls.
Closed cell - $3.00 to $5.00 per sq ft, R-7 per inch, acts as a vapor barrier, rigid, adds structural strength. Default for Knoxville crawl spaces, rim joists, below-grade walls and metal buildings.

Per equivalent R-value, closed cell costs roughly 2x open cell because the chemistry is denser and more expensive. That is why most Knoxville attic retrofits use open cell at 5.5 to 7 inches of depth to hit R-20 to R-25, and most crawl space jobs use 2 to 3 inches of closed cell for both insulation and vapor control. See the closed cell vs open cell deep-dive for the full comparison.

What Changes a Knoxville Spray Foam Quote

Two Knoxville homes next door to each other can get different per-square-foot numbers. The drivers:

Foam type and depth - the single biggest cost driver. Open cell at 5.5 inches vs closed cell at 3 inches for the same R-value, different numbers.
Access - a Farragut walk-up attic quotes lower per square foot than a tight 1920s Bearden knee-wall attic. Same for crawl spaces: a 36-inch tall crawl beats a 24-inch belly-crawl.
Removal of old insulation - fiberglass batt removal and disposal typically adds $0.50 to $1.00 per sq ft to a Knoxville attic job.
Substrate prep - crawl spaces with active moisture, rot or mold need remediation before spraying. Metal buildings need surface cleaning. Both add to the quote.
Code and permit requirements - Tennessee building code requires a thermal or ignition barrier over spray foam in living spaces. For conditioned conversions (barndominiums), permits and inspection may apply.
Total square footage - most Knoxville installers price smaller jobs higher per square foot to cover mobilization. The per-square-foot number drops as the job scales up.

Worked Example: 2,000 sq ft Knoxville Attic Retrofit

Say you own a 2,000 square foot ranch in West Knoxville with a vented attic, R-19 fiberglass batt on the attic floor, and ductwork running through the attic. You want to pull the batt, spray foam the roof deck to turn the attic into conditioned space, and bring the whole assembly up to current code.

Open cell spray foam on the roof deck at 5.5 inches (R-20 to R-25 depending on substrate temperature): 2,000 sq ft at $2.50 per sq ft = $5,000.
Existing fiberglass batt removal and disposal: 2,000 sq ft at $0.75 per sq ft = $1,500.
Gable end wall foam (open cell at 3.5 inches, 200 sq ft): $500.
Total: roughly $7,000 installed as a typical Knoxville market example, with a written quote and written warranty terms before work starts. Your home may quote higher or lower.

The same job in a tight 1930s Bearden bungalow with knee walls and limited access would quote closer to the top of the range. The same job in a 2010s Farragut home with full stand-up attic access would quote near the bottom. The 2026 Knoxville cost guide walks through more examples.

Rebates and Tax Credits That Reduce Knoxville Cost

Two programs regularly knock real dollars off a Knoxville spray foam quote:

TVA EnergyRight rebates for qualifying insulation upgrades across the Tennessee Valley. See the TVA rebate guide for current amounts and eligibility.
Federal 25C Energy Efficient Home Improvement Credit under the Inflation Reduction Act - up to $1,200 per year for insulation improvements.

Combined, these can take $500 to $2,500 off a typical Knoxville attic or crawl space job. Always verify current program details with TVA, your local power company, and a licensed tax advisor.