Attic Insulation Types and R-Values: Blown-In, Batt, Spray Foam, and Radiant Barrier

Your attic is responsible for up to 25% of heat loss in the average home. Choosing the right insulation — and hitting the right R-value — is one of the highest-ROI upgrades a homeowner can make. This guide breaks down every major attic insulation type, what R-value you actually need by climate zone, realistic cost ranges, and how to choose the best option for your situation.

What Is R-Value and Why Does It Matter?

R-value measures thermal resistance — how well a material slows heat transfer. Higher R-value means better insulation. But R-value per inch varies by material, and required total R-value depends on where you live.

DOE-Recommended R-Values for Attics by Climate Zone

Zone 1–2 (South Florida, Hawaii): R-30 to R-49
Zone 3 (Gulf Coast, Southwest): R-38 to R-60
Zone 4 (Mid-Atlantic, Pacific Northwest): R-38 to R-60
Zone 5–6 (Midwest, Northeast, Mountain states): R-49 to R-60
Zone 7–8 (Northern Minnesota, Alaska): R-49 to R-60

Most homes in Zone 4–6 need R-49 to R-60 in the attic. If your home was built before 1990, chances are good you’re sitting at R-11 to R-19 — far below current recommendations.

Blown-In Insulation

Blown-in insulation (also called loose-fill) is installed by blowing cellulose, fiberglass, or mineral wool fibers into the attic cavity using a machine.

Types of Blown-In Material

Cellulose: Made from 80–85% recycled newsprint. R-value of 3.2–3.8 per inch. Naturally fire-resistant due to borate treatment. Excellent for filling irregular cavities and around obstructions. Settles slightly over time (5–10%), so contractors install 10–15% extra.

Fiberglass (loose-fill): R-value of 2.2–2.7 per inch. Doesn’t settle. Doesn’t absorb moisture. Requires a higher depth to reach target R-values compared to cellulose. Popular in humid climates because it dries quickly if wet.

Mineral Wool (rock wool): R-value of 3.0–3.3 per inch. Fire-resistant to 1,800°F. Excellent sound dampening. More expensive but performs better in fire risk zones.

Cost of Blown-In Attic Insulation

Cellulose: $0.50–$1.25 per square foot installed (1,000 sq ft attic = $500–$1,250)
Fiberglass loose-fill: $0.75–$1.50 per square foot installed
Mineral wool: $1.50–$2.50 per square foot installed

Most contractors quote blown-in as a total job. Expect $1,500–$3,500 for a typical 1,000–1,500 sq ft attic going from R-11 to R-49.

Best Use Cases for Blown-In

Topping off existing insulation to hit target R-values
Attics with irregular framing, pipes, and obstructions
Air-sealing first, then blown-in on top
DIY projects (home centers rent blowing machines for free with purchase of bags)

Batt Insulation

Fiberglass or mineral wool batts are the pink and yellow rolls you’ve seen in every home improvement store. They’re pre-cut to fit standard 16” or 24” joist spacing.

R-Value per Inch for Batts

Standard fiberglass batts: R-2.9 to R-3.8 per inch
High-density fiberglass batts: R-3.8 to R-4.3 per inch
Mineral wool batts: R-3.7 to R-4.2 per inch

A standard 2×6 framing cavity (5.5 inches) filled with fiberglass gets you about R-19. Achieving R-49 requires stacking multiple batt layers.

Cost of Batt Insulation

Standard fiberglass batts (installed): $0.50–$1.00 per square foot
High-density fiberglass (installed): $1.00–$1.50 per square foot
Mineral wool batts (installed): $1.50–$2.50 per square foot
DIY materials only: $0.25–$0.75 per square foot

Performance Limitations

Batts are only as good as their installation. Gaps, compression, and misalignment dramatically reduce effective R-value. A compressed batt rated R-19 may perform at R-12. Studies show that even small gaps (3%) in insulation coverage can reduce overall thermal performance by 30% or more.

Batts work best when installed by careful contractors or careful DIYers in open, unobstructed attic floors with consistent framing spacing.

Best Use Cases for Batts

New construction with consistent joist spacing
Attic floors with wide-open access
DIY projects where blown-in equipment isn’t available
Tight budgets — batts are typically the lowest cost option

Spray Foam Insulation

Spray polyurethane foam (SPF) is applied as a liquid that expands and hardens, creating both insulation and an air barrier simultaneously. Two types: open-cell and closed-cell.

Open-Cell vs. Closed-Cell Spray Foam

Open-cell spray foam:

R-value: 3.5–3.6 per inch
Expands dramatically (up to 100x)
Soft, spongy texture
Vapor permeable — moisture can pass through
Lower cost than closed-cell
Best for interior applications, sound dampening

Closed-cell spray foam:

R-value: 6.0–7.0 per inch — the highest of any insulation type
Rigid, structural
Excellent vapor barrier
Best for exterior applications, basements, crawl spaces
Higher cost

Cost of Spray Foam

Open-cell: $0.50–$0.65 per board foot installed (1 board foot = 1 sq ft, 1 inch thick)
Closed-cell: $1.00–$1.50 per board foot installed

For a 1,000 sq ft attic floor at 4 inches thick:

Open-cell: $2,000–$2,600
Closed-cell: $4,000–$6,000

Spray foam is also used to insulate the attic roof deck (underside of roof sheathing), creating a conditioned unvented attic. This approach costs more but delivers exceptional performance, especially in hot climates.

Best Use Cases for Spray Foam

Air sealing at the attic plane (rim joists, penetrations, top plates)
Unvented attic assembly (insulating roof deck instead of floor)
Very tight spaces where batting or blowing won’t work
Homes needing combined vapor barrier + insulation

Radiant Barriers

A radiant barrier is a reflective material (typically aluminum foil laminated to a substrate) that reduces radiant heat gain from a hot roof. It doesn’t have a traditional R-value because it works differently — by reflecting radiant heat rather than absorbing it.

How Radiant Barriers Work

In summer, roof sheathing can reach 150–160°F. It radiates heat downward toward the attic floor. A radiant barrier installed on the attic floor (or under the roof sheathing) reflects 95–97% of that radiant heat, keeping attic temperatures 20–30°F cooler.

Effectiveness by Climate

Radiant barriers deliver the best ROI in hot, sunny climates (IECC Zones 1–3). In Zone 4 and above, the benefit is primarily in summer, and the ROI is less compelling.

DOE studies show radiant barriers can reduce cooling costs by 5–10% in hot climates — not transformational, but meaningful.

Cost of Radiant Barriers

Foil radiant barrier (stapled to rafters, DIY): $0.15–$0.30 per square foot materials
Installed by contractor: $0.75–$1.50 per square foot

For a 1,500 sq ft attic: $1,100–$2,250 installed.

Important: Don’t Let Radiant Barriers Substitute for Mass Insulation

Radiant barriers only address radiant heat. They do nothing for conductive or convective heat transfer, which is what mass insulation (blown-in, batts, foam) addresses. A radiant barrier on top of R-11 attic floor insulation is not a substitute for upgrading to R-49.

Best Use Cases for Radiant Barriers

Hot, sunny climates (Florida, Texas, Arizona, Southern California)
Homes with high cooling bills
Combination with adequate mass insulation, not as a replacement

Choosing the Right Attic Insulation for Your Home

Step 1: Check Current R-Value

Measure the depth of existing insulation:

Fiberglass batts: multiply depth (inches) × 3.1
Cellulose loose-fill: multiply depth (inches) × 3.5
No insulation: R-0

Find your climate zone at the DOE’s website and calculate the gap.

Step 2: Air Seal First

No insulation upgrade delivers full performance unless air sealing is done first. Common attic air leaks include:

Top plates along exterior walls
Can light penetrations
Attic hatch perimeter
Plumbing and electrical penetrations
Chimney chase gaps

Air sealing with caulk and spray foam before adding insulation can improve effectiveness by 20–40%.

Step 3: Match Insulation Type to Budget and Situation

Situation	Best Choice
Topping off existing insulation, moderate budget	Blown-in cellulose or fiberglass
Open attic floor, DIY project	Batts (fiberglass)
Unvented attic or roof deck insulation	Closed-cell spray foam
Hot climate, want to add cooling savings	Blown-in + radiant barrier
Maximum performance, budget not primary concern	Closed-cell spray foam or dense-pack cellulose

ROI: When Does Attic Insulation Pay Off?

Upgrading from R-11 to R-38+ in an average 1,500 sq ft home typically saves $200–$400 per year in heating and cooling costs. At a project cost of $1,500–$3,000, that’s a 5–10 year payback — and the improvement lasts 30+ years.

The EPA estimates that proper attic and floor insulation can reduce total energy bills by 15% on average.

Federal tax credits are available for insulation under the Residential Clean Energy Credit and the Energy Efficient Home Improvement Credit. Through 2032, homeowners can claim 30% of insulation upgrade costs (up to $1,200) on their federal return. Check with a tax professional for your specific situation.

Questions to Ask Your Insulation Contractor

Before hiring, ask:

What R-value will this project achieve, and how does that compare to the DOE recommendation for my climate zone?
Will you air seal before installing insulation?
Are you using a blower door test to identify air leaks?
What material are you using, and why?
Is the material fire-rated and mold-resistant?
What’s the warranty on materials and installation?
Are you properly licensed and insured for this work in my state?

A good insulation contractor will recommend air sealing as a first step, discuss climate-zone appropriate R-values, and explain material tradeoffs honestly. Get at least 3 quotes — insulation pricing varies significantly by region and contractor.