Insulation R-Value Reference Guide

Complete guide to insulation R-values by climate zone, insulation type comparison, coverage calculations, vapor barrier requirements, and proper installation techniques for maximum energy efficiency.

R-Value Requirements by Climate Zone

Understanding Climate Zones

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.

Recommended R-Values by Location & Application

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

Additional Considerations by Zone

Zones 1-3 (Hot climates): Focus on attic insulation and radiant barriers to reduce cooling costs
Zones 4-5 (Mixed climates): Balance heating and cooling needs with good all-around insulation
Zones 6-8 (Cold climates): Maximize insulation levels, pay attention to air sealing and vapor barriers
Basements: Add R-10 to R-15 in zones 4+, R-15 to R-19 in zones 6+
Crawl spaces: Insulate walls (not floor) in most climates with R-10 to R-15

Insulation Types & R-Value Comparison

R-Value Per Inch by Insulation Type

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

Fiberglass Batts

R-value: R-3.2 per inch (R-13 for 3.5", R-19 for 6", R-30 for 9.5")
Pros: Low cost, DIY-friendly, widely available, non-flammable
Cons: Loses R-value when compressed, doesn't air seal, irritates skin
Installation: Cut to fit, friction-fit between studs/joists

Blown Cellulose

R-value: R-3.7 per inch (highest loose-fill option)
Pros: Eco-friendly (recycled paper), fills gaps well, good air sealing
Cons: Settles over time, absorbs moisture, requires blower
Installation: Dense-pack walls at 3.5 lbs/cu ft, loose attics at 1.5 lbs/cu ft

Closed-Cell Spray Foam

R-value: R-6.5 per inch (highest R-value per inch available)
Pros: Air and moisture barrier, adds structural strength, no settling
Cons: Most expensive, requires professional install, vapor impermeable
Installation: 2-3" typical in walls, 4-6" in attics, cures in seconds

Open-Cell Spray Foam

R-value: R-3.7 per inch (lower than closed-cell)
Pros: Excellent air seal, allows some moisture permeability, good sound dampening
Cons: Still expensive, not a moisture barrier, requires more thickness
Installation: 3-5" in walls, 6-10" in attics, expands greatly

Coverage Calculations & Material Estimating

How to Calculate Insulation Needed

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.

Batt Insulation Coverage by R-Value

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

Blown Insulation Coverage per Bag

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

Example Calculation

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 Barrier Requirements by Climate Zone

Critical Vapor Barrier Guidelines

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.

Vapor Barrier Requirements by Zone

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

Vapor Retarder Classes

Class I (0.1 perm or less): Polyethylene sheet, aluminum foil, vapor barrier paint
Class II (0.1 to 1.0 perm): Kraft-faced fiberglass, unfaced EPS foam
Class III (1.0 to 10 perm): Latex paint, unfaced fiberglass, housewrap

Installation Best Practices

Install continuous 6-mil poly over studs before drywall in cold climates
Overlap seams by 6 inches minimum, tape all seams
Seal around all penetrations (outlets, pipes, ducts)
Use kraft-faced batts with facing toward warm side
Never install vapor barrier on both sides of wall (traps moisture)

Special Situations

Attics: No vapor barrier needed on attic floor in most zones (insulation is permeable)
Cathedral ceilings: Vapor barrier on interior side, requires ventilation above insulation
Basement walls: No vapor barrier between wall and insulation; rigid foam provides barrier
Air conditioning climates: Consider vapor drive from outside in during summer
Spray foam: Closed-cell foam acts as vapor barrier, no additional barrier needed

Step-by-Step Installation Process

Determine Required R-Value for Your Zone

•Look up your climate zone (1-8) based on your location
•Identify required R-values for attic, walls, floors, and basement
•Check local building codes which may exceed IECC minimums
•Consider going above code for better energy savings
•Document current R-value if adding to existing insulation
•Plan for continuous insulation with no gaps or compression

Choose Appropriate Insulation Type

•Match insulation type to application (batts for cavities, blown for attics)
•Consider R-value per inch needed to fit cavity depth
•Factor in budget: fiberglass cheapest, spray foam most expensive
•Evaluate DIY capability vs. professional installation needed
•Check for moisture issues that may require special products
•Select faced or unfaced batts based on vapor barrier needs

Prepare Work Area & Safety Equipment

•Clear attic or work area of stored items and debris
•Ensure adequate lighting (LED work lights recommended)
•Wear respirator/dust mask (N95 minimum for fiberglass)
•Use protective clothing: long sleeves, gloves, safety glasses
•Set up ventilation if working in enclosed space
•Have fire extinguisher nearby, no open flames in attic

Air Seal Before Insulating

•Seal all air leaks with caulk or expanding foam (critical step)
•Seal around electrical boxes, pipes, ducts, and wire penetrations
•Use fire-rated caulk around chimneys and flues (3-inch gap)
•Install rigid foam dam around attic hatches, seal edges
•Seal top plates where walls meet attic floor
•Fill large gaps with rigid foam board before insulation

Install Vapor Barrier (If Required)

•Determine if vapor barrier needed based on climate zone
•Install 6-mil polyethylene on warm side (interior in cold climates)
•Overlap seams by 6 inches, tape with contractor tape
•Cut X-slits for electrical boxes, tape around box edges
•Staple to studs or joists every 12-16 inches
•For kraft-faced batts, flanges act as vapor retarder

Install Batt Insulation (Walls/Floors)

•Measure cavity dimensions, cut batts slightly oversized
•Use sharp utility knife with new blade for clean cuts
•Friction-fit batts between studs/joists without compressing
•Split batts around obstacles (pipes, wires) to maintain full thickness
•Staple kraft facing flanges to face of studs (not sides)
•Fill all gaps completely - no voids or compressed areas

Install Blown Insulation (Attics)

•Rent insulation blower from home improvement store (usually free)
•Mark desired depth on rafters using ruler (add 1" for settling)
•Start at farthest point from attic access, work backward
•Maintain consistent blower setting for even coverage
•Build baffles/chutes at eaves to maintain soffit ventilation
•Do not cover recessed lights unless IC-rated (keep 3" clearance)

Insulate Rim Joists & Cantilevers

•Cut rigid foam board to fit rim joist cavities exactly
•Seal edges with expanding foam or caulk for airtight fit
•Or use spray foam to insulate and air seal simultaneously
•For cantilevers, dense-pack with cellulose or use spray foam
•Ensure no air gaps between floor and rim joist insulation
•Install to achieve R-15 minimum in cold climates

Maintain Ventilation & Clearances

•Install baffles between rafters at eaves for air flow
•Maintain 1-2 inch air gap above insulation in cathedral ceilings
•Keep insulation 3 inches away from non-IC recessed lights
•Do not cover soffit or ridge vents with insulation
•Ensure attic has adequate ventilation (1:150 ratio or 1:300 with vapor barrier)
•Block off dropped soffits but allow air flow behind

Final Inspection & Quality Check

•Inspect for gaps, compression, or missed areas
•Verify full depth achieved throughout attic (check markers)
•Ensure even distribution with no high or low spots
•Confirm all air sealing completed before covering
•Check that vapor barriers are continuous with sealed seams
•Photograph installation for records before covering with drywall
•Verify ventilation pathways remain clear and unobstructed

Best Practices & Common Mistakes

DO:

Air seal all penetrations BEFORE installing insulation
Install insulation to full depth without gaps or compression
Place vapor barrier on warm side (interior in cold climates)
Maintain ventilation in attics and cathedral ceilings
Split batts around obstacles to maintain full thickness
Wear proper PPE (respirator, gloves, long sleeves, goggles)
Insulate rim joists and cantilevers for complete thermal envelope
Check local codes which may require higher R-values than IECC

DON'T:

Compress insulation (reduces R-value significantly)
Install vapor barriers on both sides of wall (traps moisture)
Cover non-IC-rated recessed lights with insulation
Block soffit or ridge vents with insulation (causes moisture issues)
Leave gaps between batts or around obstacles
Install insulation without proper PPE (causes irritation)
Forget to air seal before insulating (most common mistake)
Use wrong R-value for your climate zone (wastes money or underperforms)

Required Tools & Materials

Essential Tools

• Utility knife with extra blades
• Tape measure and straightedge
• Staple gun and staples (for batts)
• Insulation blower (rental for blown insulation)
• Caulk gun and foam gun
• Headlamp or work lights
• Dust pan or shop vacuum

Safety Equipment

• N95 respirator or dust mask
• Safety glasses or goggles
• Work gloves (leather or rubber)
• Long-sleeve shirt and pants
• Hard hat (for attic work)
• Knee pads
• First aid kit

Installation Materials

• Insulation (batts or bags of blown)
• 6-mil polyethylene vapor barrier
• Contractor tape for seams
• Caulk (acoustic sealant preferred)
• Expanding foam sealant
• Vent baffles/chutes for eaves
• Rigid foam for rim joists

Optional But Helpful

• Insulation support rods (for floors)
• Marking stakes for attic depth
• Portable fan for ventilation
• Foam board insulation cutter
• Infrared thermometer
• Attic stair cover kit
• Recessed light covers (IC boxes)