Free Insulation Calculator - R-Value, Batts & Cost (2026)

Q: What R-value do I need for my attic?

Most building codes recommend R-38 to R-60 for attics in cold climates and R-30 to R-38 in moderate climates. The Department of Energy provides zone-specific recommendations, but R-38 is a good baseline for most U.S. homes.

Q: How much does spray foam insulation cost?

Open-cell spray foam typically costs $1.00 to $1.50 per square foot installed, while closed-cell runs $1.50 to $3.50 per square foot. Closed-cell provides a higher R-value per inch and acts as a vapor barrier, which can offset the higher cost in moisture-prone areas.

Q: Can I install insulation myself?

Fiberglass batts and blown-in cellulose are popular DIY-friendly options. Blown-in requires renting a blower machine. Spray foam insulation is best left to professionals due to the specialized equipment and safety requirements. Always wear proper protective gear when handling insulation.

Q: How much insulation do I need for a 1,200 square foot attic?

For a 1,200 sq ft attic at R-38, you need approximately 10 bags of blown-in cellulose (each bag covers roughly 40 sq ft at the required depth) or 14 bundles of R-38 fiberglass batts. Use this calculator to get exact counts for your R-value target. Always add 10-15% overage for gaps and irregular areas around joists and blocking.

Q: What R-value do I need for exterior walls?

Most residential exterior walls need R-13 to R-21. A standard 2x4 stud wall with fiberglass batts achieves R-15. Upgrading to 2x6 framing allows R-21 batts for about $0.30 per sq ft more. In climate zones 5-8 (northern U.S.), building codes often require R-20 or better for exterior walls, so check local code before ordering.

Q: How much does it cost to insulate an attic?

Blown-in insulation for a 1,200 sq ft attic to R-38 costs $1,700 to $2,100 installed. Spray foam runs higher: open-cell is $2,400 to $4,800 and closed-cell is $4,800 to $9,600 for the same area. DIY blown-in cellulose cuts cost roughly in half when you rent the blower machine from a home improvement store.

Q: What is the most cost-effective insulation type?

Blown-in cellulose offers the lowest installed cost per R-value unit, averaging $0.35 to $0.55 per square foot. It fills irregular spaces well, uses recycled content, and installs fast. Fiberglass batts come close in material cost but leave more air gaps around wiring and pipes. Closed-cell spray foam costs the most but also seals air leaks completely and adds rigidity to walls.

Area to Insulatesq ft

Location

Desired R-Value

Insulation Type

Your Location (optional - adjusts for local labor costs)

Insulation Estimate

Coverage Area1,000 sq ft

LocationAttic

Insulation TypeFiberglass Batts

Target R-ValueR-30

R-Value per Inch3.2

Thickness Needed9.4 inches

Batts Needed12 batts

Estimated Total Cost

$1,500.00

Total Cost$1,500.00

Materials50%

Labor50%

Free to use. No signup needed.

Recommended R-Values by Location:

Walls: R-13 to R-21
Attic: R-30 to R-60
Floor / Crawlspace: R-19 to R-30

Insulation R-Value & Cost Guide

Required R-values by climate zone, material comparisons, and energy savings data.

What R-Value Insulation Do I Need?

Required R-values vary by climate zone, ranging from R-13 walls/R-30 attic (South) to R-21 walls/R-60 attic (North).

Zone 1-2 (Southern US): R-13 walls, R-30 attic, R-13 floors
Zone 3-4 (Mid-Atlantic, Midwest): R-15–R-20 walls, R-38–R-49 attic
Zone 5-6 (Northern US): R-20–R-21 walls, R-49–R-60 attic
Zone 7-8 (Alaska, extreme cold): R-21+ walls, R-60+ attic

R-value is additive. A 2×4 wall with R-13 batts + R-5 continuous foam sheathing = R-18 total.

Key Takeaways

Southern US: R-13 walls, R-30 attic
Northern US: R-20+ walls, R-49–R-60 attic
R-values are additive when layered

Insulation Types & Cost Comparison

Fiberglass batts are the cheapest at $0.50–$1.50/sq ft installed, while closed-cell spray foam costs $1.50–$3.50/sq ft but provides the highest R-value per inch.

Fiberglass batts: $0.50–$1.50/sq ft, R-3.1–R-3.7 per inch
Blown-in fiberglass: $0.75–$1.50/sq ft, R-2.5–R-3.7 per inch
Cellulose (blown): $0.75–$1.25/sq ft, R-3.2–R-3.8 per inch
Open-cell spray foam: $0.75–$1.50/sq ft, R-3.5–R-3.7 per inch
Closed-cell spray foam: $1.50–$3.50/sq ft, R-6.0–R-7.0 per inch
Rigid foam board (XPS): $0.75–$2.00/sq ft, R-5.0 per inch

Key Takeaways

Fiberglass batts: cheapest at $0.50–$1.50/sq ft
Closed-cell spray foam: highest R per inch (R-6–R-7)
Cellulose: best value for attic blown-in

Where to Insulate for Maximum Energy Savings

Attic insulation provides the highest ROI — insulating an uninsulated attic can reduce heating/cooling bills by 25–40%.

Attic (highest priority): Blown cellulose or fiberglass to R-38–R-60
Exterior walls: Batts or blown-in to R-13–R-21 (new construction or gut remodel)
Crawl space/basement: R-10–R-19 on rim joists and walls
Ductwork: R-6–R-8 on exposed ducts in unconditioned spaces

Sealing air leaks before insulating is critical. Air sealing alone can reduce energy costs by 10–20%. Insulation without air sealing loses much of its effectiveness.

Key Takeaways

Attic insulation: highest ROI (25–40% savings)
Seal air leaks before insulating
Duct insulation: R-6–R-8 in unconditioned spaces

How to Use This Calculator

Enter the area to insulate

Input the total square footage of walls, attic, floor, or crawlspace you need to insulate.

Select location and R-value

Choose where the insulation will be installed and the desired R-value based on your climate zone and building code requirements.

Choose insulation type

Pick from fiberglass batts, blown-in fiberglass, blown-in cellulose, open-cell spray foam, or closed-cell spray foam.

Review thickness and cost breakdown

See the required thickness, number of batts or bags needed, plus a material and labor cost estimate.

Insulation Calculation Formulas

Thickness = R-Value / R-per-Inch
Units Needed = Area / Coverage per Unit
Material Cost = Area x Cost per Sq Ft
Labor Cost = Area x Labor Rate per Sq Ft
Total Cost = Material Cost + Labor Cost

Where:

R-per-Inch: = Fiberglass 3.2, Cellulose 3.5, Open-Cell 3.7, Closed-Cell 6.5
Coverage per Unit: = Varies by product: 88 sf/batt, 40 sf/bag, etc.

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Frequently Asked Questions

What R-value do I need for my attic?

Most building codes recommend R-38 to R-60 for attics in cold climates and R-30 to R-38 in moderate climates. The Department of Energy provides zone-specific recommendations, but R-38 is a good baseline for most U.S. homes.

How thick does insulation need to be?

Thickness depends on the insulation type and target R-value. For example, fiberglass batts provide about R-3.2 per inch, so R-30 requires roughly 9.4 inches. Closed-cell spray foam at R-6.5 per inch only needs about 4.6 inches for the same R-value.

Is blown-in insulation better than batts?

Blown-in insulation fills gaps and irregular spaces more completely, making it ideal for attics and retrofit projects. Batts work well in new construction with standard stud spacing. Both achieve similar R-values per inch; the best choice depends on your application.

How much does spray foam insulation cost?

Open-cell spray foam typically costs $1.00 to $1.50 per square foot installed, while closed-cell runs $1.50 to $3.50 per square foot. Closed-cell provides a higher R-value per inch and acts as a vapor barrier, which can offset the higher cost in moisture-prone areas.

Can I install insulation myself?

Fiberglass batts and blown-in cellulose are popular DIY-friendly options. Blown-in requires renting a blower machine. Spray foam insulation is best left to professionals due to the specialized equipment and safety requirements. Always wear proper protective gear when handling insulation.

How much insulation do I need for a 1,200 square foot attic?

For a 1,200 sq ft attic at R-38, you need approximately 10 bags of blown-in cellulose (each bag covers roughly 40 sq ft at the required depth) or 14 bundles of R-38 fiberglass batts. Use this calculator to get exact counts for your R-value target. Always add 10-15% overage for gaps and irregular areas around joists and blocking.

What R-value do I need for exterior walls?

Most residential exterior walls need R-13 to R-21. A standard 2x4 stud wall with fiberglass batts achieves R-15. Upgrading to 2x6 framing allows R-21 batts for about $0.30 per sq ft more. In climate zones 5-8 (northern U.S.), building codes often require R-20 or better for exterior walls, so check local code before ordering.

How much does it cost to insulate an attic?

Blown-in insulation for a 1,200 sq ft attic to R-38 costs $1,700 to $2,100 installed. Spray foam runs higher: open-cell is $2,400 to $4,800 and closed-cell is $4,800 to $9,600 for the same area. DIY blown-in cellulose cuts cost roughly in half when you rent the blower machine from a home improvement store.

What is the most cost-effective insulation type?

Blown-in cellulose offers the lowest installed cost per R-value unit, averaging $0.35 to $0.55 per square foot. It fills irregular spaces well, uses recycled content, and installs fast. Fiberglass batts come close in material cost but leave more air gaps around wiring and pipes. Closed-cell spray foam costs the most but also seals air leaks completely and adds rigidity to walls.

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