What R-value insulation do I need?

R-value requirements depend on climate zone and location. Attics typically need R-38 to R-60. Exterior walls need R-13 to R-21. Floors over unheated spaces need R-25 to R-30. Check local building codes for specific requirements.

How many rolls of insulation do I need for walls?

Each roll of R-13 fiberglass batt covers about 40 square feet (standard 15-inch width). Divide total wall area by 40. A 12x8 foot wall equals 96 sq ft, needing 2.4 rolls. Add 10% for cuts and fitting around obstacles.

Is blown-in or batt insulation better?

Blown-in insulation fills gaps better and is easier for attics, achieving better coverage. Batts are more DIY-friendly for walls and have consistent R-value if installed properly. Both are effective when correctly installed without gaps or compression.

Can I add insulation over existing insulation?

Yes, adding insulation over existing material is common and effective. For attics, install unfaced batts or blown insulation over existing material. Avoid compressing existing insulation. In walls, injection foam can supplement existing batts.

How thick should attic insulation be?

For R-38 (minimum code in many areas), fiberglass batts need to be 10-12 inches thick. For R-49, aim for 14-16 inches. Blown cellulose is denser and reaches R-38 at about 10 inches. More insulation is generally better for energy savings.

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Insulation Calculator

Calculate insulation for walls, attics, and energy savings

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Last verified: February 2026Accuracy tested

Calculated in your browser — we never store your dataIncludes standard waste factors

Wall Length (ft)

Wall Height (ft)

R-Value

Price per Sq Ft ($)

● National avg · updated Feb 20

Sources & Methodology

Formula: Bags = Area / Coverage per bag

Coverage varies by R-value and product

Source: Manufacturer specifications & Energy Star guidelines

View full methodology & accuracy testing

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How to Use the Insulation Calculator

Estimate insulation needs for walls or attics based on R-value requirements. Get accurate batt counts for your energy efficiency project. Use our square footage calculator to measure wall and attic areas precisely.

Understanding R-Values

R-value measures thermal resistance—higher numbers mean better insulation. Local building codes specify minimum R-values based on climate zone. Common recommendations:

Walls: R-13 to R-21 depending on wall thickness
Attics: R-30 to R-49+ depending on climate
Floors: R-13 to R-30

Calculation Basis

We estimate based on standard fiberglass batts covering approximately 48 square feet per package. Blown-in insulation requires different calculations based on settled density.

Energy Efficiency Tips

Insulation is just one component of energy efficiency. Also consider air sealing, vapor barriers, and proper ventilation. For major projects, consider an energy audit to identify priority areas.

Related Construction Calculators

Insulation goes hand-in-hand with drywall and lumber for wall framing. If you're finishing an attic, check our roofing calculator for any repairs needed. Calculate the return on investment of energy improvements.

Frequently Asked Questions

Measure attic square footage, then divide by the coverage per bag or roll. Most attic insulation bags cover 30-70 square feet depending on R-value and product. A 1,000 sq ft attic at R-38 typically needs 15-25 bags of blown insulation.