Insulation R-Value Charts & Guides
Code requirements, material data, and calculators for every project.
What Is R-Value in Insulation?
R-value measures thermal resistance—the ability of insulation to resist heat flow. The higher the R-value, the greater the insulating effectiveness. R-value is expressed as h·ft²·°F/BTU in the United States, representing the temperature difference needed to transfer one BTU of heat per hour through one square foot of material.
The R-value you need depends on three factors: your climate zone (determined by heating and cooling degree days), the location being insulated (attic, walls, basement, etc.), and local building codes. The International Energy Conservation Code (IECC) establishes minimum R-value requirements, though many energy-conscious homeowners exceed these minimums for better comfort and energy savings.
R-values are additive when materials are layered. For example, R-19 fiberglass batts plus R-11 batts equals R-30 total. However, compression reduces R-value—a compressed R-19 batt performs below its rated value. Proper installation without compression, gaps, or voids is essential for achieving rated performance.
R-Value Insulation Chart
This chart shows R-value per inch, typical applications, and cost ranges for all common insulation materials. Use this data to compare options for your project.
| Material | R-Value/Inch | Best For | Cost/Sq Ft | DIY? |
|---|---|---|---|---|
| Closed-Cell Spray Foam | R-6.0 – R-7.0 | Rim joists, crawl spaces, moisture barriers | $1.00–$2.00 | No |
| Polyisocyanurate (Polyiso) | R-5.6 – R-6.5 | Exterior sheathing, roofing, continuous insulation | $0.70–$1.00 | Yes |
| Extruded Polystyrene (XPS) | R-5.0 | Below-grade, foundation, high-moisture areas | $0.50–$0.75 | Yes |
| Expanded Polystyrene (EPS) | R-3.6 – R-4.2 | ICF walls, EIFS, cost-effective rigid foam | $0.25–$0.50 | Yes |
| Open-Cell Spray Foam | R-3.5 – R-3.8 | Interior walls, sound control, cathedral ceilings | $0.44–$0.65 | No |
| Mineral Wool (Rockwool) | R-3.0 – R-3.3 | Fire resistance, soundproofing, exterior walls | $0.60–$1.20 | Yes |
| Fiberglass Batts | R-2.9 – R-3.8 | Standard wall cavities, attics, floors | $0.30–$0.50 | Yes |
| Blown-In Fiberglass | R-2.2 – R-2.7 | Attic floors, wall retrofits | $0.50–$1.00 | Yes* |
| Cellulose (Blown-In) | R-3.2 – R-3.8 | Attics, dense-pack walls, retrofits | $0.60–$1.20 | Yes* |
| Radiant Barrier | N/A** | Attic rafters (hot climates only) | $0.15–$0.50 | Yes |
*Blower machine rental available at home improvement stores. **Radiant barriers reduce radiant heat transfer; they don't have an R-value but can reduce cooling loads by 5–10% in hot climates.
2021 IECC Insulation Requirements by Climate Zone
The International Energy Conservation Code (IECC) establishes minimum R-value requirements based on climate zone. These are legal minimums—exceeding them improves energy efficiency and comfort. Use our R-Value Calculator to find your zone by ZIP code.
| Zone | Ceiling/Attic | Wood Frame Wall | Floor | Basement Wall | Crawl Space |
|---|---|---|---|---|---|
| Zone 1 | R-30 | R-13 | R-13 | R-0 | R-0 |
| Zone 2 | R-38 | R-13 | R-13 | R-0 | R-0 |
| Zone 3 | R-38 | R-20 or R-13+5ci | R-19 | R-5ci | R-5ci |
| Zone 4 (except Marine) | R-49 | R-20 or R-13+5ci | R-19 | R-10ci or R-13 | R-10ci |
| Zone 4 Marine | R-49 | R-20+5ci or R-13+10ci | R-30 | R-10ci or R-13 | R-10ci |
| Zone 5 | R-49 | R-20+5ci or R-13+10ci | R-30 | R-15ci or R-19 | R-15ci |
| Zone 6 | R-49 | R-20+5ci or R-13+10ci | R-30 | R-15ci or R-19 | R-15ci |
| Zone 7 | R-49 | R-20+10ci or R-13+15ci | R-38 | R-15ci or R-19 | R-15ci |
| Zone 8 | R-49 | R-20+10ci or R-13+15ci | R-38 | R-15ci or R-19 | R-15ci |
"ci" = continuous insulation (uninterrupted by framing). R-13+5ci means R-13 cavity insulation plus R-5 continuous exterior insulation. Local codes may differ—always verify with your building department.
R-Value Per Inch Comparison
R-value per inch determines how much thickness you need to achieve your target R-value. Higher R-per-inch materials achieve the same thermal resistance in less space—critical for walls with limited cavity depth or cathedral ceilings where every inch matters.
Highest R-Value Per Inch
| Material | R/Inch |
|---|---|
| Closed-Cell Spray Foam | R-6.5 |
| Polyisocyanurate | R-6.0 |
| Extruded Polystyrene (XPS) | R-5.0 |
| Expanded Polystyrene (EPS) | R-4.0 |
| High-Density Fiberglass | R-3.8 |
Standard R-Value Per Inch
| Material | R/Inch |
|---|---|
| Open-Cell Spray Foam | R-3.7 |
| Cellulose (Blown) | R-3.5 |
| Mineral Wool Batts | R-3.3 |
| Fiberglass Batts | R-3.2 |
| Blown-In Fiberglass | R-2.5 |
Thickness Required for R-49 Attic Insulation
IECC Climate Zones Explained
The United States is divided into 8 climate zones based on heating degree days (HDD) and cooling degree days (CDD). Your zone determines minimum insulation requirements under the IECC building code.
Denver, Chicago, Boston, Salt Lake City. Cold winters, moderate summers. Attic R-49, wall R-20+5ci typical.
Minneapolis, Milwaukee, Burlington. Very cold winters. Same requirements as Zone 5, but more savings from exceeding minimums.
Duluth, northern New England, northern tier. Severe winters require R-49 attic, R-20+10ci walls, R-38 floors.
Alaska only. Extreme cold requires maximum insulation at all envelope locations.
Miami, Key West, Hawaii. Cooling-dominated. R-30 attic minimum, air sealing critical for humidity control.
Houston, Phoenix, South Florida. R-38 attic, radiant barriers beneficial. Vapor barriers face exterior.
Atlanta, Dallas, Los Angeles. Mixed heating/cooling. R-38 attic, continuous insulation becoming common.
Washington DC, Seattle, St. Louis. R-49 attic required. Marine (4C) subzone has stricter wall requirements.
Insulation Cost Guide
Insulation costs vary by material, installation method (DIY vs. professional), and project scope. These are 2024-2025 national average costs including materials and labor where applicable.
| Project Type | DIY Cost | Installed Cost | For 1,000 Sq Ft |
|---|---|---|---|
| Attic: Blown-In Fiberglass (R-49) | $0.50–$0.75/sf | $1.00–$1.50/sf | $1,000–$1,500 |
| Attic: Blown-In Cellulose (R-49) | $0.60–$0.90/sf | $1.20–$1.80/sf | $1,200–$1,800 |
| Attic: Open-Cell Spray Foam (R-38) | — | $1.50–$2.50/sf | $1,500–$2,500 |
| Attic: Closed-Cell Spray Foam (R-49) | — | $3.00–$5.00/sf | $3,000–$5,000 |
| Wall Cavity: Blown-In (Retrofit) | — | $1.50–$3.00/sf | $1,500–$3,000 |
| Basement Walls: Rigid Foam (R-15) | $0.75–$1.25/sf | $2.00–$3.50/sf | $2,000–$3,500 |
| Crawl Space: Closed-Cell Foam | — | $2.50–$4.50/sf | $2,500–$4,500 |
| Rim Joist: Closed-Cell Foam | — | $3.00–$5.00/lf | $450–$750 (avg home) |
Insulation Installation Guides
Proper installation is as important as choosing the right material. Gaps, compression, and missing vapor barriers can reduce effective R-value by 30% or more. Our guides cover both DIY projects and what to expect from professional installation.
Attic Insulation
Air sealing, vapor barriers, ventilation baffles, and achieving R-49 or higher. Covers blown-in, batts, and spray foam options.
Read guideWall Insulation
New construction vs. retrofit approaches. Dense-pack cellulose, drill-and-fill, and continuous exterior insulation strategies.
Read guideBasement Insulation
Interior vs. exterior approaches, moisture management, rim joist air sealing, and meeting code for conditioned basements.
Read guideCrawl Space Insulation
Encapsulation vs. vented crawl spaces, vapor barriers, and choosing between floor insulation and crawl space wall insulation.
Read guideGarage Insulation
Insulating attached garage walls, ceilings above living space, and garage doors for improved comfort and energy savings.
Read guideHow to Install Blown-In
Step-by-step DIY guide for blown-in fiberglass and cellulose. Equipment rental, safety, and achieving consistent depth.
Read guideInsulation Material Comparisons
Choosing between insulation types? These side-by-side comparisons analyze cost, performance, installation requirements, and best applications for each material pairing.
Open-Cell vs. Closed-Cell Spray Foam
R-value, moisture permeability, cost, and when to use each type.
Fiberglass vs. Cellulose
Cost, settling, fire resistance, and installation for attic blowing.
Fiberglass vs. Mineral Wool
Fire rating, soundproofing, moisture resistance, and cost differences.
XPS vs. EPS Rigid Foam
Moisture absorption, R-value, cost, and foundation applications.
Faced vs. Unfaced Insulation
When you need a vapor retarder and which direction it should face.
Batts vs. Blown-In Insulation
Coverage quality, labor, cost, and which is better for attics.
Frequently Asked Questions
What R-value do I need for my attic?
The minimum R-value for attics depends on your climate zone. Zones 1-2 require R-30 to R-38, Zone 3 requires R-38, and Zones 4-8 require R-49 per the 2021 IECC code. However, many experts recommend R-60 for cold climates (Zones 5-8) for optimal energy savings. Use our R-Value Calculator to find the specific requirement for your ZIP code.
How thick should my insulation be?
Thickness depends on the material's R-value per inch and your target R-value. For R-49 attic insulation: blown fiberglass needs about 19 inches, cellulose needs 14 inches, and closed-cell spray foam needs only 7.5 inches. Use our Thickness Calculator to determine exact depth for any R-value and material combination.
What is the best insulation for walls?
For new construction, fiberglass or mineral wool batts sized to your wall cavity (R-13 for 2x4, R-19-21 for 2x6) are most common. Add continuous exterior insulation (rigid foam or mineral wool boards) to reduce thermal bridging. For retrofits without removing drywall, blown-in cellulose or fiberglass via small holes is the standard approach. Spray foam offers the best air sealing but costs 2-3x more. See our Wall Insulation Guide for detailed recommendations.
Is spray foam worth the extra cost?
Spray foam provides the highest R-value per inch (R-6.5 for closed-cell) and creates an air barrier, eliminating the need for separate air sealing. It's worth the extra cost for rim joists, crawl spaces, cathedral ceilings, and anywhere air sealing is critical. For standard attics with accessible air sealing, blown-in cellulose or fiberglass often provides better ROI. See our spray foam cost analysis for payback calculations.
Do I need a vapor barrier with insulation?
It depends on climate and location. In cold climates (Zones 4-8), a vapor retarder (Class II or III) should face the warm-in-winter side (interior). In hot-humid climates (Zones 1-2), it should face the exterior. In mixed climates, "smart" vapor retarders that adjust permeability are often recommended. Never sandwich insulation between two vapor barriers—moisture must be able to dry in at least one direction. See our faced vs. unfaced guide for details.
Can I add insulation on top of existing insulation?
Yes, adding insulation over existing material is common practice for attic upgrades. The new insulation does not need a vapor retarder—only the bottom layer should have one. Ensure the existing insulation is dry and not compressed. If upgrading from R-19 to R-49, you're adding R-30 worth of material. Blown-in products work best for layering over existing batts. Address any air leaks before adding insulation for maximum effectiveness.
What's the difference between R-value and U-value?
R-value measures thermal resistance (higher is better), while U-value measures thermal conductance (lower is better). They are reciprocals: U = 1/R. R-value is used for insulation materials in the US, while U-value is often used for windows and whole-assembly performance. An R-20 wall assembly has a U-value of 0.05. The IECC code specifies both, with U-values used for windows and doors.
How much can I save by adding insulation?
Savings depend on your current insulation level, target level, climate, and energy costs. The DOE estimates that upgrading from R-11 to R-49 attic insulation can reduce heating/cooling costs by 10-50%, with the largest savings in extreme climates. A typical attic upgrade from R-19 to R-49 costs $1,000-$1,500 for a 1,000 sq ft attic and may save $200-$400 annually in Zones 5-7. Use our Savings Calculator for a personalized estimate.
Insulation Calculators & Tools
Free interactive tools to help you determine requirements, estimate costs, and choose the right insulation for your project.
Independent Resource: InsulationRValues.com is not affiliated with any manufacturer, retailer, or installation company. Our recommendations are based on building science data from the U.S. Department of Energy, Oak Ridge National Laboratory, Building Science Corporation, and IECC building codes.