Insulation R-value chart: recommended R-values by climate zone for attics, walls, and floors, R-value per inch for fiberglass, cellulose, mineral wool, spray foam, and rigid foam, plus coverage and vapor barrier rules.
Doing this on a real job? Insulate the attic: materials, tools and steps sized to your numbers.
Get the planSee what your wall really delivers with studs, foam and siding counted in the wall R-value calculator.
Turn these targets into bags, rolls and cost with the insulation calculator, or add up a stack of layers with its R-value calculator.
The United States is divided into 8 climate zones for insulation requirements. Higher zones (colder climates) require higher R-values. Zone 1 is the warmest (South Florida, Hawaii), Zone 8 is the coldest (Alaska).
Rule: Meeting or exceeding the minimum R-value for your zone ensures energy efficiency and code compliance.
| Climate Zone | Attic/Ceiling | Wall Cavity | Floor | Example Locations |
|---|---|---|---|---|
| Zone 1 | R-30 to R-49 | R-13 to R-15 | R-13 | South FL, Hawaii |
| Zone 2 | R-30 to R-60 | R-13 to R-15 | R-13 to R-19 | Central FL, South TX, South CA |
| Zone 3 | R-30 to R-60 | R-13 to R-21 | R-19 to R-25 | North FL, Central TX, AZ, NC, GA |
| Zone 4 | R-38 to R-60 | R-15 to R-21 | R-25 to R-30 | VA, KY, TN, MO, KS, NM, NV |
| Zone 5 | R-49 to R-60 | R-20 to R-21 | R-25 to R-30 | IL, IN, OH, PA, UT, CO |
| Zone 6 | R-49 to R-60 | R-20 to R-21 | R-25 to R-30 | NY, WI, MI, WY, VT, ME |
| Zone 7 | R-49 to R-60 | R-21 | R-25 to R-30 | MN, ND, MT, Northern NY/ME |
| Zone 8 | R-49 to R-60 | R-21 | R-30 | Alaska, Northern Canada |
| Insulation Type | R-Value Per Inch | Best Applications | Cost Range |
|---|---|---|---|
| Fiberglass Batts | R-3.1 to R-3.4 | Wall cavities, standard attics, floors | $0.40-0.70/sq ft |
| Blown Fiberglass | R-2.2 to R-2.7 | Attic floors, hard-to-reach areas | $0.60-1.00/sq ft |
| Blown Cellulose | R-3.6 to R-3.8 | Attics, walls (dense-pack), eco-friendly | $0.80-1.20/sq ft |
| Mineral Wool (Rockwool) | R-3.0 to R-3.3 | Fire resistance, sound dampening | $1.00-1.50/sq ft |
| Open-Cell Spray Foam | R-3.6 to R-3.8 | Walls, rim joists, air sealing | $1.20-2.00/sq ft |
| Closed-Cell Spray Foam | R-6.0 to R-6.5 | High performance, moisture barrier, roof decks | $2.00-3.50/sq ft |
| Rigid Foam Board (EPS) | R-3.6 to R-4.2 | Basement walls, exterior sheathing | $0.50-1.00/sq ft |
| Rigid Foam Board (XPS) | R-5.0 | Moisture resistance, below grade | $0.75-1.25/sq ft |
| Polyisocyanurate (Polyiso) | R-6.0 to R-6.5 | Roof insulation, commercial applications | $1.00-1.75/sq ft |
Formula: (Area in sq ft × Desired R-value) ÷ R-value per inch = Total inches needed
Then convert inches to bags/packages based on product coverage at that depth.
| R-Value | Thickness | Stud Size | Sq Ft per Package |
|---|---|---|---|
| R-13 | 3.5 inches | 2x4 walls | 40-88 sq ft (15" or 23" width) |
| R-15 | 3.5 inches | 2x4 walls (high-density) | 32-64 sq ft |
| R-19 | 6.25 inches | 2x6 walls, floors | 48-75 sq ft |
| R-21 | 5.5 inches | 2x6 walls (high-density) | 42-67 sq ft |
| R-30 | 9.5 inches | Attic floors, 2x10 | 58-107 sq ft |
| R-38 | 12 inches | Attic floors | 48-90 sq ft |
| Material Type | Bag Weight | R-30 Coverage | R-38 Coverage | R-49 Coverage |
|---|---|---|---|---|
| Blown Fiberglass | 19-30 lbs | 40-72 sq ft | 31-57 sq ft | 24-44 sq ft |
| Blown Cellulose | 25-30 lbs | 36-42 sq ft | 28-33 sq ft | 22-26 sq ft |
| Mineral Wool (loose) | 24-30 lbs | 35-45 sq ft | 27-35 sq ft | 21-27 sq ft |
Scenario: Insulating 1,200 sq ft attic in Zone 5 (need R-49)
Step 1: Choose insulation: Blown cellulose at R-3.7 per inch
Step 2: Calculate depth needed: R-49 ÷ R-3.7 = 13.2 inches needed
Step 3: Check bag coverage: 1 bag covers 22-26 sq ft at R-49 depth
Step 4: Calculate bags: 1,200 sq ft ÷ 24 sq ft (average) = 50 bags
Step 5: Add 10% waste: 50 × 1.1 = 55 bags total
Result: Order 55 bags of blown cellulose, rent blower
Vapor barriers control moisture movement through walls and ceilings. Incorrect placement can trap moisture and cause mold, rot, and insulation failure. The barrier always goes on the warm side (in winter).
Rule: In cold climates (zones 5-8), vapor barrier goes on interior (warm) side. In hot-humid climates (zones 1-2), may not be needed or goes on exterior side.
| Climate Zone | Vapor Barrier Needed? | Placement | Type/Material |
|---|---|---|---|
| Zone 1-2 (Hot-Humid) | Usually not required | If used, exterior side | Class III vapor retarder or none |
| Zone 3 (Mixed-Humid) | Optional, depends on specifics | Interior side if used | Class II or III vapor retarder |
| Zone 4 (Mixed) | Recommended | Interior (warm) side | Class II vapor retarder, kraft-faced batts OK |
| Zone 5 (Cold) | Required | Interior (warm) side | Class I or II vapor retarder, poly recommended |
| Zone 6-7 (Very Cold) | Required | Interior (warm) side | Class I vapor retarder, 6-mil poly required |
| Zone 8 (Extreme Cold) | Required | Interior (warm) side | Class I vapor retarder, 6-mil poly minimum |
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