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Uniform worksheet · Home Improvement

Form RET-207 · Effective August 2026 · Borrower’s copy

Insulation Calculator

Calculate insulation for attic, walls, or crawl space.

Inputs

$

Total Area

0 sqft

Bags/Rolls

0

Estimated Cost

$0

How to Use This Insulation Calculator

See Methodology

Our free insulation calculator determines how much insulation you need for your attic, walls, or crawl space. Enter your area dimensions and desired R-value for material quantities and cost estimates.

R-value measures thermal resistance — higher numbers mean better insulation. Recommended values vary by climate zone. Our calculator suggests appropriate R-values for your location.

The calculator compares blown-in vs batt insulation options. Blown-in is better for irregular spaces; batts are cost-effective for new construction.

Climate zone lookup is essential before choosing insulation depth. The DOE divides the U.S. into 8 climate zones, each with different recommended R-values for attics, walls, and foundations. For example, a home in zone 5 (like Minneapolis) needs R-49 to R-60 in the attic, while zone 2 (like Houston) requires only R-30 to R-49. Use the DOE's zone map or enter your zip code to determine your exact requirements.

Air sealing before insulating is arguably more important than the insulation itself. Seal air leaks around recessed lights, plumbing penetrations, attic hatches, and rim joists with caulk or foam before adding insulation. Without air sealing, heated air bypasses insulation through convective loops, reducing effective R-value by 20-40%. This is the single biggest bang-for-your-buck energy improvement in most homes.

Professional vs. DIY cost varies significantly: blown-in attic insulation runs $1-$2/sq ft professionally installed but only $0.50-$1/sq ft as a DIY project when you rent the blower machine from a home improvement store. Batts are the easiest DIY option — no special equipment needed, just a utility knife, straightedge, and protective gear. For safety, always wear an N95 mask, safety goggles, gloves, and long sleeves when handling fiberglass insulation, as the tiny glass fibers irritate skin, eyes, and lungs. Cellulose is less irritating but still warrants respiratory protection.

Vapor barrier placement depends on your climate: in cold climates, it goes on the warm (interior) side of the insulation to prevent condensation within the wall cavity. In hot, humid climates, it goes on the exterior side. Incorrect vapor barrier placement can trap moisture and cause mold or rot, so verify your local building code requirements. Some insulation types, like faced fiberglass batts, include an integrated vapor barrier — a separate polyethylene sheet may not be needed.

Related Topics

insulation calculator ·attic insulation calculator ·how much insulation do i need ·R-value calculator ·insulation cost estimator ·

Frequently Asked Questions about Home Insulation

  • How much insulation do I need for my attic?

    Measure your attic floor area in square feet, then determine the target R-value based on your climate zone — most regions require R-38 to R-60, which translates to roughly 12–20 inches of blown fiberglass. Subtract any existing insulation depth from the target, then use our calculator to determine the number of bags needed for the remaining depth.

  • What R-value should my insulation be?

    Your required R-value depends on your climate zone as defined by the DOE: zones 1–2 (southern states) need R-30 to R-49, zones 3–4 (middle states) need R-38 to R-60, and zones 5–7 (northern states) need R-49 to R-60 for attics. Wall cavities typically need R-13 to R-21. Check your local building code for the exact minimum for your area.

  • How much does insulation cost per sq ft?

    Installed costs vary by type: blown fiberglass runs $1–$2 per sq ft for R-30, blown cellulose costs $1–$1.50, and fiberglass batts are the cheapest at $0.50–$1 per sq ft. DIY installation saves roughly 50% compared to professional installation, though blown-in materials may require renting a machine from a home improvement store.

  • What is the difference between blown-in and batt insulation?

    Blown-in insulation (fiberglass or cellulose) fills irregular spaces, around wiring, and into cavities that batts can't reach, making it ideal for attics and retrofit projects. Batt insulation comes in pre-cut rolls that fit snugly between studs, making it cost-effective for new construction and wall cavities. Blown-in requires a blower machine; batts can be installed with basic hand tools.

  • Do I need a vapor barrier with insulation?

    In cold climates, the vapor barrier should be installed on the warm (interior) side of the insulation to prevent condensation. In hot, humid climates, it goes on the exterior side. Not all insulation types require a separate vapor barrier — some batts come with a built-in kraft facing. Always check your local building codes, as requirements vary significantly by region and wall assembly type.

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