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Recommended R Value By Zone

Where these numbers come from

The table below is summarised from the ENERGY STAR recommended home insulation R-values page, checked on 2026-10-29. ENERGY STAR says its guidance is based on the 2021 International Energy Conservation Code (IECC) residential provisions. It describes cost-effective levels for retrofitting existing wood-framed homes. Your local code may require different levels for new construction or renovations, and codes are updated over time, so confirm with your building department.

Attic and floor targets (retrofit)

Source: ENERGY STAR, as published on 2026-10-29. These are total levels to aim for, not amounts to add.

Walls, basements and crawlspaces

ENERGY STAR's page also says that when siding is replaced on an uninsulated wood-frame wall, insulation can be blown into the empty cavities, with insulative sheathing added in colder zones (R5 in Zone 3, R5 to R10 in Zones 4 to 8). For basement or crawlspace walls, it lists R5 sheathing or R13 batts in Zone 3, R10 sheathing or R13 batts in Zones 4A and 4B, and R15 sheathing or R19 batts in Zones 4C and 5 to 8. Read the source for the exact wording.

Finding your climate zone

U.S. climate zones are defined county by county in the IECC and shown on maps from ENERGY STAR and the U.S. Department of Energy. Zone 1 is the hottest (southern Florida, Hawaii); Zones 7 and 8 are the coldest (northern Minnesota, Alaska). Letters A, B and C mark moist, dry and marine sub-zones. If you live in Canada, the U.S. zones do not apply directly; see Canada R-value requirements.

Turning a target into depth

1. Measure existing depth in several places and identify the material.
2. Estimate existing R with the R-value chart.
3. Subtract from the target to get R to add.
4. Divide by the new product's R per inch to get depth.
5. Use the bag chart for bags.

The attic insulation calculator runs steps 2 to 4.

Why "already 3 to 4 inches" has a lower target

Adding insulation has diminishing returns. The first inches save the most; each extra inch saves a little less. ENERGY STAR's retrofit table reflects what tends to be cost-effective, so a home that already has some insulation gets a slightly lower top-up target than an empty attic.

Worked example

Figures below are illustrative examples (2026-10-29), not quotes or guarantees.

Assumptions: a home in Zone 5 with 4 in of old loose-fill fiberglass (assumed R2.5/in, about R10). ENERGY STAR's target for an attic that already has 3 to 4 in is R49. R to add = 49 − 10 = 39. With new loose-fill at an assumed R2.5/in, add about 15.6 in. If the attic were empty, the target would be R60, needing about 24 in of the same product.

Beyond R-value

Before adding insulation, seal air leaks, make sure soffit vents are not blocked (see attic ventilation baffles), keep insulation clear of heat sources as required by code and product labels, and check for moisture or pests. If you find vermiculite, do not disturb it.

Mixed and humid climates

In hot, humid zones, attic insulation reduces heat entering from a sun-baked roof, and air sealing keeps humid attic air out of the house. Ductwork in the attic matters a lot; seal and insulate ducts. In mixed climates, both heating and cooling benefit. In cold zones, heat loss dominates and ice dams are a concern.

Ducts in the attic

If heating or cooling ducts run through the attic, seal joints with approved mastic or tape and insulate them. Leaky ducts can undo much of the benefit of attic insulation.

Choosing between table and code

For a retrofit with no permit, the ENERGY STAR table is a practical target. For permitted work or new construction, your local code governs. If they differ, use the higher level unless a professional advises otherwise.

Next steps

Once you know your target, check for hazards, air seal, fit baffles, then insulate. Use the blown-in calculator or batt calculator to plan materials.

Worked example, illustrative

Illustrative example (2026-10-29): a house in Zone 5 with about 4 inches of old fiberglass. Assumption: old layer ≈ R-11. Target R-49 to R-60 for existing attics with some insulation. Add R-38 to R-49 of new loose-fill. Check the bag chart for depth and bag count and air seal first.

Finding your zone

In the U.S., climate zones are mapped by county; ENERGY STAR's page links a map. In Canada, use NRCan resources and your provincial code, since U.S. zones do not map directly. If you are near a zone boundary, use the colder zone's target for extra margin. Zone 1 covers the warmest areas, while Zones 7 and 8 cover very cold regions. Elevation can make a local climate colder than its neighbours, so check the map by county rather than guessing from latitude. Record your zone with your project notes.

Quick tip

Note your zone and target on your project sheet.

FAQ

Is R60 too much for a mild climate?

Follow the table for your zone; extra R has smaller payback in mild climates.

Do I have to meet these levels?

They are recommendations for retrofits. Codes may set requirements for permitted work.

Where is my zone?

Check the IECC or ENERGY STAR maps by county.

Does this apply in Canada?

No; use provincial codes and NRCan guidance.

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