Find the recommended R-value for your attic, walls, floor, or basement by US climate zone. Calculate insulation thickness by material type, compare options side by side, and estimate project cost. Updated for 2026 DOE standards.
✓Verified: US Department of Energy IECC Climate Zone Standards & InsulationRValues.com — April 2026
📋 Your Location & Building
Find your zone at energystar.gov or enter your state below
Each location has different DOE recommendations
R-
Enter 0 if new construction or unknownEnter 0–80.
New construction may access more insulation options
Recommended R-Value
—
Thickness Needed by Material
⚠️ Disclaimer: R-value recommendations are based on 2026 DOE IECC guidelines. Always verify with your local building code, as requirements may exceed DOE minimums. Consult a licensed insulation contractor for project-specific recommendations.
Enter existing insulation R-value (0 = none)Enter 0–80.
Insulation Thickness Needed
—
⚠️ Disclaimer: Thickness calculations use average R-values per inch. Actual thickness needed varies by product manufacturer, density, and installation conditions. Always check the manufacturer’s specification sheet for your specific product.
Was this calculator helpful?
✓ Thanks for your feedback!
📋 Insulation Cost Estimate
sq ft
Total square footage of surfaceEnter a valid area.
R-
Enter target R-value for your projectEnter target R-value (1–100).
DIY = materials cost only
Estimated Project Cost
—
⚠️ Disclaimer: Cost estimates are based on 2026 national average pricing. Actual costs vary by region, contractor, accessibility, and specific product. Get multiple contractor quotes for accurate project pricing.
Was this calculator helpful?
✓ Thanks for your feedback!
Sources & Methodology
✓R-value recommendations sourced from DOE/IECC 2021 climate zone standards. R-value per inch data from manufacturer spec sheets (Owens Corning, Rockwool, Icynene) and InsulationRValues.com 2026 chart.
Official DOE recommended R-values for attic, wall, floor, and basement insulation by climate zone. The basis for all R-value recommendations in this calculator.
Real-world R-value per inch data for all insulation materials with cost benchmarks. Source for material R-values per inch, thickness calculations, and cost ranges used in this calculator.
Material-specific R-value ranges, cost per square foot benchmarks, and material selection guidance used in the cost estimator section of this calculator.
Methodology: Thickness Needed (in) = (Target R-Value − Current R-Value) / R-Value per InchProject Cost = Area (sq ft) x Thickness (in) x Cost per Sq Ft per Inch
DOE R-value targets by zone and location from IECC 2021. R-value per inch: Fiberglass loose 3.2, Batts 3.4, Cellulose 3.5, Mineral wool 4.1, Open-cell foam 3.6, Closed-cell foam 6.5, XPS 5.0, Polyiso 6.0, EPS 4.0. Costs: materials $0.25–$1.50/sq ft/in; pro install adds labor multiplier of 1.5–3x depending on material.
Last reviewed: April 2026
Insulation R-Value Guide 2026 — Everything You Need to Know
Insulation is one of the highest-return home improvement investments available. Properly insulating your home to the correct R-value for your climate zone typically saves 10 to 50 percent on annual heating and cooling costs, depending on your starting point. Understanding R-value, climate zones, and material choices helps you make the best decision for your budget and climate.
💡 Key fact: R-value measures thermal resistance — the higher the number, the better the insulation performance. R-values are additive: two layers of R-13 equals R-26 total. The DOE divides the US into 8 climate zones with increasingly higher R-value requirements for colder regions.
DOE Recommended R-Values by Climate Zone (2026)
Climate Zone
States/Regions
Attic
Wall (cavity)
Floor
Basement Wall
Zone 1–2
S. FL, HI, TX Gulf Coast
R-30–R-49
R-13
R-13
R-0–R-10
Zone 3
TX, GA, SC, N. AZ
R-38–R-49
R-13–R-15
R-19–R-25
R-5–R-10
Zone 4
Mid-Atlantic, KY, TN, NM
R-38–R-60
R-13+R-5ci or R-20
R-25–R-30
R-10–R-15
Zone 5
OH, PA, NY, Midwest, CO
R-49–R-60
R-13+R-10ci or R-20
R-30–R-38
R-15
Zone 6
MN, WI, MT, N. New England
R-49–R-60
R-15+R-15ci or R-21
R-38
R-15
Zone 7–8
N. MN, ND, Interior Alaska
R-49–R-60+
R-21+R-15ci
R-38
R-15–R-20
ci = continuous insulation (rigid foam on exterior of wall sheathing, eliminates thermal bridging)
Insulation Materials — R-Value Per Inch & Cost (2026)
Material
R-Value per Inch
Cost (pro installed)
Best For
Closed-Cell Spray Foam
R-6.0–7.0
$1.50–$4.00/sq ft/in
Air sealing, space-constrained, moisture resistance
Polyiso Rigid Foam Board
R-5.6–6.5
$0.50–$1.20/sq ft/in (material)
Exterior continuous insulation, roof
XPS Rigid Foam Board
R-5.0
$0.40–$0.90/sq ft/in (material)
Below grade, exterior walls, cold climates
EPS Rigid Foam Board
R-3.8–4.4
$0.25–$0.60/sq ft/in (material)
Below slab, exterior, cost-effective rigid
Mineral Wool (Rockwool)
R-4.0–4.2
$0.80–$1.50/sq ft
Fire resistance, soundproofing, moisture
Open-Cell Spray Foam
R-3.5–3.7
$1.00–$2.00/sq ft/in
Interior walls, soundproofing, cathedral ceilings
Cellulose Blown-In
R-3.2–3.8
$0.50–$1.00/sq ft
Attics, retrofit wall cavities, eco-friendly
Fiberglass Batts
R-2.9–3.8
$0.40–$1.20/sq ft
Standard walls, floors, budget-friendly
Fiberglass Loose-Fill
R-2.2–2.9
$0.40–$1.00/sq ft
Attics, deep blanket coverage
Which Insulation Material Should You Choose?
For most attics: Blown-in cellulose or fiberglass is the most cost-effective solution. These materials can be applied over existing insulation and blown to any depth. Most homes in Zones 4 through 6 need 14 to 18 inches of blown-in to reach R-49 to R-60. This is one of the best ROI home improvements available, typically paying back in 2 to 4 years through energy savings.
For exterior walls (new construction): Fiberglass or mineral wool batts in the stud cavity, plus continuous rigid foam on the exterior in Zones 5 and above. A 2x6 wall with R-21 mineral wool batt plus R-10 XPS on the exterior delivers a whole-wall R-value around R-27 after accounting for thermal bridging through studs.
For retrofit walls (without opening them): Dense-pack cellulose blown in through small holes drilled in the siding or interior plaster is the most practical option. At R-3.5 to R-3.8 per inch, it fills a 2x4 cavity to approximately R-13.
For basements and crawlspaces: Closed-cell spray foam (2 to 3 inches gives R-12 to R-21 with a built-in vapor barrier) or rigid foam board against the concrete wall with a framed wall over it. Never use fiberglass batts against concrete — they absorb moisture and lose R-value.
Understanding Thermal Bridging
Thermal bridging is one of the most important concepts in building science that most homeowners do not know about. It occurs when heat conducts through structural elements — typically wood studs — that interrupt the cavity insulation. Research shows that thermal bridging through standard 2x4 framing at 16 inches on center reduces the effective whole-wall R-value by approximately 20 percent. A wall with R-13 cavity insulation has an effective whole-wall R-value closer to R-10 to R-11 due to thermal bridging.
The solution is continuous exterior insulation (CI) — a layer of rigid foam applied over the entire exterior wall sheathing before siding. Even R-5 of continuous foam dramatically reduces thermal bridging and can increase effective whole-wall R-value by 30 to 40 percent without changing the cavity insulation. This is why DOE Zone 4 and above recommendations include continuous insulation requirements.
Insulation ROI — Energy Savings by Location
Attic insulation (most homes): Adding insulation from R-0 to R-49 saves 10 to 25 percent on annual heating and cooling costs. Payback period: 2 to 4 years at typical energy prices.
Air sealing + attic insulation together: Savings of 15 to 30 percent are common. Air sealing is the highest-leverage improvement — close gaps before adding insulation depth.
Wall insulation retrofit: More expensive per R-value added than attic insulation, typically 5 to 12 percent energy savings. Payback period: 5 to 15 years depending on existing insulation level and energy prices.
Basement and crawlspace insulation: Often overlooked but significant, especially in Zones 4 to 6. Can save 5 to 15 percent on heating bills and dramatically improve comfort on ground floors.
Frequently Asked Questions
DOE-recommended attic R-values: Zone 1-2 (south FL, HI): R-30 to R-49. Zone 3 (TX, GA, SC): R-38 to R-49. Zone 4 (Mid-Atlantic, KY, TN): R-38 to R-60. Zone 5 (OH, PA, NY, Midwest): R-49 to R-60. Zone 6 (MN, WI, MT): R-49 to R-60. Zone 7-8 (Alaska extremes): R-49 to R-60+. Most US homes in Zones 4 through 6 need R-49 to R-60 in the attic.
R-value measures thermal resistance — how well insulation resists the flow of heat. The higher the R-value, the better the insulating performance. R-value is calculated as material thickness divided by thermal conductivity (k-value). R-values are additive: two layers of R-13 equals R-26 total. Higher R-values are needed in colder climates where the temperature difference between inside and outside is greater.
R-value per inch by material: Closed-cell spray foam: R-6.0 to R-7.0 (highest). Polyiso rigid foam board: R-5.6 to R-6.5. XPS rigid foam: R-5.0. Open-cell spray foam: R-3.5 to R-3.7. Mineral wool (Rockwool): R-4.0 to R-4.2. Cellulose blown-in: R-3.2 to R-3.8. Fiberglass batts: R-2.9 to R-3.8. Closed-cell spray foam is ideal when space is limited but costs 5 to 10 times more than fiberglass.
Thickness needed = Target R-value divided by R-value per inch of your material. Example: to reach R-49 using fiberglass batts (R-3.4/inch): 49 / 3.4 = 14.4 inches. Using cellulose (R-3.5/inch): 49 / 3.5 = 14 inches. Using closed-cell spray foam (R-6.5/inch): 49 / 6.5 = 7.5 inches. Our Thickness Calculator mode above does this automatically.
The DOE divides the US into 8 climate zones: Zone 1 (hot-humid, southern FL, HI), Zone 2 (hot, TX Gulf Coast, AZ), Zone 3 (warm, TX, GA, SC), Zone 4 (mixed, Mid-Atlantic, KY, NM), Zone 5 (cool, OH, PA, NY, Midwest, CO), Zone 6 (cold, MN, WI, MT), Zone 7 (very cold, northern MN, ND, high-altitude CO), Zone 8 (subarctic, interior AK). Higher zone numbers require higher R-values.
Spray foam wins on R-value per inch (R-6.5 vs R-3.4), air sealing, and moisture resistance. Fiberglass wins on cost (3 to 8x cheaper per sq ft) and DIY-friendliness. Choose closed-cell spray foam for air-sealing critical areas, space-constrained applications, basements, and high-performance builds. Choose fiberglass batts for standard open-cavity walls, floors, and attics where cost is the primary concern.
Thermal bridging occurs when heat conducts through structural wood studs that bypass cavity insulation, reducing the effective whole-wall R-value by about 20 percent. A wall with R-13 cavity insulation has an effective R-value closer to R-10 to R-11. Continuous rigid foam on the exterior eliminates thermal bridging and is required by code in Zone 4 and above. Even R-5 exterior foam dramatically improves whole-wall performance.
Attic insulation costs $1,500 to $3,500 professionally installed for a typical 1,000 sq ft attic with blown-in fiberglass or cellulose to R-49. Spray foam for the same area costs $5,000 to $10,000. Attic insulation is one of the highest-ROI home improvements, with payback periods of 2 to 4 years through energy savings at 2026 energy prices.
Most insulation materials maintain R-value for decades if protected from moisture. Fiberglass and mineral wool can last 50 or more years. Spray foam maintains R-value for the life of the building. Cellulose may settle 5 to 10 percent over 20 years. Moisture significantly decreases R-value in any material — always address moisture sources before insulating.
Wall R-values by zone: Zones 1-2: R-13 cavity. Zone 3: R-13 to R-15 cavity. Zone 4: R-13 plus R-5 continuous exterior, or R-20 total. Zone 5: R-13 plus R-10 continuous, or R-20 total. Zone 6-8: R-15 cavity plus R-15 continuous, or R-21. A standard 2x4 wall with fiberglass provides R-13. A 2x6 wall provides R-19 to R-21.
R-13 is the standard for a 2x4 wall cavity filled with standard fiberglass batts. R-15 is achieved with high-density fiberglass or mineral wool (Rockwool) batts that fit the same 2x4 cavity but provide 15% more thermal resistance. R-15 is required by code in Zone 3 and recommended in Zones 4-5. For the best performance, combine R-15 cavity batts with continuous exterior rigid foam in colder zones.
Yes, with conditions. Attic blown-in insulation and fiberglass batts in open cavities are DIY-friendly. You can rent a blower machine from most home improvement stores. Spray foam insulation requires professional equipment and training. Rigid foam board installation on exteriors is DIY-possible but requires careful detailing. Always address air sealing before adding insulation depth — foam sealant and caulk around penetrations dramatically improves performance.