How do I find my climate zone?

The IECC divides the U.S. into eight climate zones. You can look up your county on the IECC climate zone map or use the ENERGY STAR insulation R-value table, which lists zones by state. Many states span multiple zones — for example, California ranges from Zone 3 to Zone 5, and Florida ranges from Zone 1 to Zone 3 — so check by county rather than by state name alone.

Can I add new insulation over old?

Yes, in most cases. First inspect the existing insulation for water damage, mold, compression, or pest contamination and address those issues before adding more. If the existing insulation is in good condition, you can add a new layer on top. Use the tool to calculate how much additional R-value you need by entering your existing R-value. Do not assume layers combine perfectly — gaps and compression reduce actual performance.

What is the best insulation material?

There is no single best material. Fiberglass batts are affordable and DIY-friendly. Blown-in cellulose offers higher R-per-inch and better gap-filling. Closed-cell spray foam provides the highest R-per-inch (R-6 to R-7 per inch) and acts as an air barrier and vapor retarder, but it costs significantly more. The best choice depends on your area, budget, access, and whether you need air sealing in the same step.

Do I need to air seal before insulating?

Yes. The DOE and ENERGY STAR strongly recommend air sealing before adding insulation. Insulation slows conductive heat flow, but it does not stop air leaks through gaps around wiring, plumbing, top plates, recessed fixtures, and the attic hatch. Adding insulation over unsealed leaks allows conditioned air to escape and can introduce moisture into the assembly. Seal first, then insulate.

How thick should my attic insulation be?

Thickness depends on your target R-value and the material you choose. For example, to reach R-60 with blown cellulose at about R-3.5 per inch, you need roughly 17 inches. The same R-60 with closed-cell spray foam at R-6.5 per inch would need about 9 inches. Use the depth estimator in the tool above, but always confirm against manufacturer specifications, as density, settling, and compression affect real-world performance.

Reference Guides

Home Insulation R-Value Guide

Find the recommended R-values for your climate zone — attic, walls, floors, and basement — based on U.S. Department of Energy (DOE) and ENERGY STAR guidelines.

R-Value Target & Depth Estimator

Select Your Climate Zone

Zone 4C (coastal Pacific NW) uses floor R30 and wall R15 sheathing / R19 batt, grouping with Zones 5–6.

Application Area

Existing Insulation Condition

Insulation Material (for depth calculation)

Recommended Specification

Target Thermal Resistance

R-60

ENERGY STAR / DOE guideline for Zone 4

Estimated Material Depth

~17.1 inches

Based on Blown-in cellulose (15.8–18.8 in. range).

Depth & Settling Note

Loose-fill materials settle after installation (up to 15–20% for blown cellulose). Install to the manufacturer's labeled initial thickness to achieve settled R-value.

R-Value by Climate Zone and Area

Department of Energy recommended levels for existing residential structures:

Climate Zone	Attic (Uninsulated)	Attic (Existing R11+)	Floor	Wall Sheathing / Cavity
Zone 1	R-30	R-25	R-13	R13
Zone 2	R-49	R-38	R-13	R13
Zone 3	R-49	R-38	R-19	R5 + R13
Zone 4	R-60	R-49	R-19	R10 + R13
Zone 5	R-60	R-49	R-30	R15 + R19
Zone 6	R-60	R-49	R-30	R15 + R19
Zone 7	R-60	R-49	R-38	R15 + R19
Zone 8	R-60	R-49	R-38	R15 + R19

Common Insulation Materials Comparison

Fiberglass batts

R-2.9 – 3.8 / in

Pre-cut blankets of spun glass fibers. The most common DIY batt insulation. Available faced (with a vapor retarder) or unfaced.

Pros:

Affordable and widely available
DIY-friendly for standard framing
Non-combustible

Cons:

Gaps and compression greatly reduce performance
Poor air barrier
Itches during handling

Blown-in fiberglass

R-2.2 – 2.7 / in

Loose fiberglass blown into attics with a machine. Good for covering irregular or obstructed attic spaces.

Pros:

Fills around joists and obstructions
No cutting required
Lightweight

Cons:

Lower R-per-inch than cellulose
Can settle over time
Requires blowing equipment

Blown-in cellulose

R-3.2 – 3.8 / in

Shredded, treated recycled paper blown dry or damp-sprayed. ENERGY STAR cites common materials at R-3 to R-3.5 per inch.

Pros:

Higher R-per-inch than blown fiberglass
Made from recycled content
Better air sealing than batts

Cons:

Can settle — over-fill to compensate
Absorbs moisture
Dust during installation

Open-cell spray foam

R-3.5 – 3.9 / in

Spray-applied polyurethane that expands to fill cavities. Open-cell is softer and more permeable than closed-cell.

Pros:

Expands to seal gaps and cracks
Good air barrier
Sound-dampening

Cons:

Lower R-per-inch than closed-cell
Vapor-permeable
Professional installation typically required

Closed-cell spray foam

R-6 – 7 / in

Dense spray foam that acts as insulation, air barrier, and vapor retarder in one. Highest R-per-inch of common materials.

Pros:

Highest R-per-inch available
Air barrier and vapor retarder
Adds structural rigidity

Cons:

Expensive
Requires professional installation
Blowing agents have environmental considerations

Mineral wool (rock/slag)

R-3 – 3.3 / in

Batts or loose-fill made from molten rock or slag. Naturally fire-resistant and denser than fiberglass.

Pros:

Fire-resistant without added chemicals
Better sound-dampening than fiberglass
Does not settle as much

Cons:

More expensive than fiberglass
Heavier and harder to cut
Dust during handling

Essential Air-Sealing Steps Before Insulating

Air-Seal First, Then Insulate

Insulation resists conductive heat transfer, but it does NOT stop air leaks. Before adding attic insulation:

Seal electrical wire penetrations and ceiling electrical boxes with expanding foam.
Foam around plumbing vent stacks and flues (use fire-rated sealant near chimneys).
Weatherstrip and insulate the attic access hatch or drop-down ladder.
Install rafter vent baffles to maintain a continuous air path from soffit vents to ridge exhaust.

Frequently Asked Questions

It depends on your climate zone and existing insulation. In Zones 4–8, ENERGY STAR recommends R-60 for an uninsulated attic and R-49 when 3–4 inches of insulation already exists. In Zones 2–3 the target is R-49 (R-38 with existing insulation), and in Zone 1 it is R-30 (R-25 with existing insulation). Use the tool above to get a specific recommendation for your zone.

Authoritative References & Standards

ENERGY STAR Recommended Home Insulation R-Values

R-value table by climate zone (based on 2021 IECC).

DOE Energy Saver Guide 2022

R-value recommendations and material R-per-inch data.

ENERGY STAR Well-Insulated and Sealed Attic

R-3 to R-3.5 per inch for common materials; air sealing guidance.

Building America Solution Center — Passive Ventilation

Ventilation and insulation interaction.