How much insulation a house should have depends mainly on its climate zone. This page gives the R-values ENERGY STAR recommends for adding insulation to an existing wood-framed house, zone by zone, and a lookup that finds the climate zone of any of the 3,142 US counties (and county equivalents) in the Department of Energy county table. Pick your state and county below, or read on for the full table, what the numbers mean and how to turn an R-value into inches of insulation.
Find your climate zone and recommended R-values
Recommended R-values by climate zone (ENERGY STAR)
| Climate zone | Attic, uninsulated: add | Attic with 3 to 4 in already: add | Floor |
|---|---|---|---|
| 1 | R-30 | R-25 | R-13 |
| 2 | R-49 | R-38 | R-13 |
| 3 | R-49 | R-38 | R-19 |
| 4A and 4B | R-60 | R-49 | R-19 |
| 4C, 5 and 6 | R-60 | R-49 | R-30 |
| 7 and 8 | R-60 | R-49 | R-38 |
Walls, basements and crawlspaces
- Above-ground walls (when the siding is replaced). If the wall cavities are empty, drill the sheathing and blow insulation into them before the new siding goes on. Then add insulating sheathing under the new siding: R-5 in zone 3, R-5 to R-10 in zones 4 to 8. If the wall is already an insulated 2×4 wall, ENERGY STAR suggests R-10 sheathing in zones 4 to 8.
- Basement and crawlspace walls. Zone 3: R-5 insulating sheathing or an R-13 batt. Zones 4A and 4B: R-10 sheathing or R-13 batt. Zones 4C and 5 to 8: R-15 sheathing or R-19 batt.
- Zones 1 and 2 get no wall or basement recommendation in the ENERGY STAR guidance; in these hot climates the attic is where added insulation pays back.
What R-value means
R-value is resistance to heat flow. A higher number means less heat passes through each square foot for each degree of temperature difference. R-values of layers in series simply add up: 3 inches of old insulation at about R-9 plus a new layer rated R-38 gives roughly R-47. What R-value does not capture is air leakage. Warm air escaping through gaps around light fixtures, chimneys, attic hatches and top plates carries heat straight past the insulation, which is why ENERGY STAR and DOE advise sealing air leaks in the attic floor before adding insulation on top.
R-values are also cut by compression and by gaps. A batt squeezed into a cavity shallower than its rated thickness loses R-value, and loose-fill insulation that has settled is thinner than when it was blown in. When you buy loose fill, use the coverage chart printed on the bag: manufacturers state the minimum settled thickness and the number of bags per 1,000 sq ft for each R-value.
Worked example: attic in zone 5
A house in Cook County, Illinois, is in zone 5A. Its attic has about 3 to 4 inches of old fiberglass, so the ENERGY STAR row for zones 4C, 5 and 6 says to add R-49. To see what that means in depth, divide by the R-value per inch of the product you plan to use. At R-3.7 per inch (the figure our insulation calculator uses for blown cellulose) the new layer is 49 / 3.7 = about 13-1/4 inches; at R-2.5 per inch for blown fiberglass it is about 19-1/2 inches. Those depths are why attic insulation is usually blown rather than laid as batts, and why the bag label, not a rule of thumb, should set the final depth.
Before you start: seal the attic floor, keep insulation at least 3 inches away from recessed lights not rated for insulation contact (IC), keep soffit vents clear with baffles so the roof still ventilates, and build a dam around the attic hatch so the insulation stays put. If the attic has knob-and-tube wiring, signs of moisture or mould, or vermiculite insulation (which may contain asbestos), get professional advice before disturbing it.
How many counties are in each zone
| IECC zone | Counties and equivalents |
|---|---|
| 1 | 8 |
| 2 | 242 |
| 3 | 700 |
| 4 | 834 |
| 5 | 768 |
| 6 | 461 |
| 7 | 120 |
| 8 | 9 |
Which climate zone map? The county table is the DOE/PNNL 2015 edition, which follows the IECC climate zone map used from the 2004 to the 2018 editions of the code. The 2021 IECC redrew the map and moved some counties into a different (mostly warmer) zone, and the ENERGY STAR guidance is written for the 2021 zones. In most counties nothing changed, but if your county is near a zone boundary, or you are building to a specific code edition, confirm the zone with your local building department.
New construction and code requirements
The ENERGY STAR figures on this page are for improving an existing house. New houses and additions must meet the energy code adopted where you live, which may be an edition of the IECC, a state code or a local amendment, and the required values differ by edition. For a permit, ask your building department which code applies and use its tables.
Frequently asked questions
How much attic insulation do I need?
For an existing attic with no insulation, ENERGY STAR recommends bringing it to R-30 in zone 1, R-49 in zones 2 and 3, and R-60 in zones 4 to 8. If there are already 3 to 4 inches, add R-25 (zone 1), R-38 (zones 2 and 3) or R-49 (zones 4 to 8).
What climate zone am I in?
Use the lookup above: choose your state and county. It uses the DOE/PNNL county table, which lists the IECC climate zone (1 to 8 with a moisture letter A, B or C) and the Building America climate region for each county.
What does the letter after the zone number mean?
The moisture regime: A is moist, B is dry and C is marine. Zone 4C, for example, is the marine climate of western Oregon and Washington.
Is more insulation always better?
Each extra inch saves less than the one before, which is why the recommendations stop at R-60. Air sealing usually gives more benefit per dollar than going beyond the recommended R-value.
Sources and method
The zone for each county is taken from the DOE county table, which we extracted from the PDF with a script (3,142 rows, every state and DC) and spot-checked against the printed pages. The recommended R-values are the ENERGY STAR figures, matched to each zone. Our only additions are the lookup itself and the arithmetic in the worked examples.
- ENERGY STAR (US EPA and DOE), Recommended Home Insulation R-Values, retrofit guidance for existing wood-framed buildings (read 24 October 2026). ENERGY STAR notes that the guidance is based on the 2021 International Energy Conservation Code, Residential Provisions, Table R402.1.3.
- US Department of Energy, Building America Best Practices Series Vol. 7.3, Guide to Determining Climate Regions by County (Pacific Northwest National Laboratory, PNNL-17211 Rev. 3, August 2015): county table Version 6 and the climate region definitions.
- Both are US Government publications. We did not copy any table from the IECC itself; for the code requirements that apply to your project, use the code adopted by your state or city.
More insulation tools
- Insulation R-value by climate zone (county lookup)
- Climate zone by county: all US counties
- Window U-factor by climate zone: ENERGY STAR limits for windows, doors and skylights, with a ZIP code lookup
- Insulation calculator: R-value from thickness, or thickness for a target R, and how many bags or batts
- All construction calculators
Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.