R-value measures how well insulation resists heat flow: the higher the number, the less heat passes through. Choosing the right level comes down to your climate zone and where the insulation goes, and ENERGY STAR publishes recommended levels for both.
ENERGY STAR recommends R-60 for an uninsulated attic in climate zones 4 through 8, R-49 to R-60 in zones 2 and 3, and R-30 to R-49 in zone 1. Heat flow is inversely proportional to R-value, so going from R-19 to R-49 cuts the heat lost through a ceiling by about 61%; seal air leaks first, which the DOE says saves 10% to 20% on heating and cooling bills.
What R-value means
R-value is resistance to heat flow. Heat flow through an insulated surface = area × temperature difference ÷ R-value, so doubling the R-value halves the heat lost. It depends on the material and its thickness; the DOE advises checking the R-value printed on the packaging or the paper backing.
How to find your climate zone
The recommendations below are keyed to the IECC climate zones, numbered 1 through 8. Lower numbers are hotter, so zone 1 needs the least ceiling insulation and zone 8 the most, which is why the table ramps from R-30 up to R-60 as the zone number rises.
Several zones split into moisture subtypes, which is why the table lists zone 4 both as "except marine" and as "marine". A warm, humid zone 4 and a cooler marine zone 4 get different floor recommendations even though the attic target is the same.
Zones are assigned by county, not by state, so one state can cover two or three zones. Look up your own county on the IECC climate-zone map to place yourself on the table.
Recommended levels by climate zone
ENERGY STAR's recommended total R-values for wood-framed houses, as published in the DOE's Energy Saver Guide:
| Climate zone | Uninsulated attic | Attic with 3 to 4 inches | Uninsulated floor |
|---|---|---|---|
| 1 | R30 to R49 | R19 to R38 | R13 |
| 2 | R49 to R60 | R38 to R49 | R13 |
| 3 | R49 to R60 | R38 to R49 | R19 |
| 4 (except marine) | R60 | R49 | R19 |
| 4 marine and 5 | R60 | R49 | R30 |
| 6 | R60 | R49 | R30 |
| 7 and 8 | R60 | R49 | R38 |
For walls, ENERGY STAR recommends adding continuous exterior insulation when siding comes off, from R5 to R15 depending on zone. These are cost-effective levels and may differ from your local building code.
Typical R-values of common materials
Typical values per inch; the label on the product is the authority:
| Material | Typical R-value per inch |
|---|---|
| Fiberglass or mineral wool batts | about 3 to 4 |
| Blown cellulose | about 3 to 4 |
| Open-cell spray foam | about 3.5 |
| Expanded polystyrene (EPS) board | about 4 |
| Extruded polystyrene (XPS) board | about 5 |
| Polyisocyanurate board | about 6 |
| Closed-cell spray foam | about 6 to 7 |
How many inches each R-value takes
Total thickness is the target R-value divided by the material's R-value per inch, using the per-inch figures above. Denser foams hit a target in far less depth, which matters when joist or stud space is fixed.
| Target | Batts or blown (3 to 4 per inch) | Open-cell foam (3.5 per inch) | Closed-cell foam (6 to 7 per inch) |
|---|---|---|---|
| R-30 | about 7.5 to 10 in | about 8.6 in | about 4.3 to 5 in |
| R-38 | about 9.5 to 13 in | about 10.9 in | about 5.4 to 6.3 in |
| R-49 | about 12 to 16 in | about 14 in | about 7 to 8 in |
| R-60 | about 15 to 20 in | about 17 in | about 8.6 to 10 in |
For example, R-49 of blown cellulose at 3 to 4 per inch works out to 49 ÷ 4 = about 12 inches at the high end and 49 ÷ 3 = about 16 inches at the low end. The same R-49 in closed-cell foam at 6 to 7 per inch is only 49 ÷ 7 = 7 to 49 ÷ 6 = about 8 inches.
How much heat each level stops
For 1,000 sq ft of ceiling with a 40°F difference between inside and the attic:
| R-value | Heat flow |
|---|---|
| R-19 | about 2,105 BTU per hour |
| R-38 | about 1,053 BTU per hour |
| R-49 | about 816 BTU per hour |
| R-60 | about 667 BTU per hour |
Over a representative season with about 4,500 heating degree days, going from R-19 to R-49 cuts that ceiling's heat loss from about 5.7 to 2.2 million BTU, about $49 a year with a 95% gas furnace at an assumed $1.35 per therm, or a broadly similar amount with a heat pump depending on your electricity rate and the pump's efficiency, before counting summer cooling. Framing and gaps lower an assembly's real R-value, so installation quality matters.
Each added step saves less than the one before it. The jump from R-19 to R-38 cuts 2,105 − 1,053 = about 1,052 BTU per hour, the next step to R-49 saves only 1,053 − 816 = about 237, and R-49 to R-60 saves 816 − 667 = about 149. That is why most zones top out at R-60 rather than chasing ever-higher numbers.
Seal air leaks first
The DOE calls air sealing one of the quickest ways to save, worth 10% to 20% on heating and cooling bills, and recommends sealing before adding insulation. Insulation slows heat conducting through a surface; it does little against air leaking around it.
Signs your home is under-insulated
Rooms over a garage or under a knee wall that run colder in winter and hotter in summer than the rest of the house point to a thin or missing layer in that assembly. Cold floors, drafts high on a wall, and a ceiling that feels cold to the touch in winter are the same symptom of heat moving through the surface too easily.
Ice dams are a cold-climate tell. Heat escaping through the ceiling melts snow on the warm upper roof, the water runs down to the cold eave and refreezes into a ridge of ice, which signals the attic is losing heat it should be holding.
Heating and cooling bills that run high compared with similar nearby homes are the bottom-line sign, since every surface below its recommended R-value leaks energy year round. Below-grade spots are easy to overlook: rim joists, crawl space walls, and basement walls are often bare, and the crawl space moisture guide covers sealing those before you insulate.
Frequently asked questions
What R-value do I need in my attic?
ENERGY STAR recommends R-60 for an uninsulated attic in zones 4 through 8, R-49 to R-60 in zones 2 and 3, and R-30 to R-49 in zone 1.
Is a higher R-value always better?
Higher stops more heat, but each step saves less than the last: R-19 to R-38 halves the heat flow, while R-38 to R-60 cuts it by about a third more.
What insulation has the highest R-value per inch?
Closed-cell spray foam and polyisocyanurate board, at about 6 to 7 and about 6 per inch.
Should I seal air leaks before adding insulation?
Yes. The DOE recommends air sealing first; it can save 10% to 20% on heating and cooling bills on its own.
How many inches of insulation do I need for R-49?
At about 3 to 4 R per inch, batts or blown fiberglass and cellulose reach R-49 in roughly 12 to 16 inches. Closed-cell spray foam at about 6 to 7 R per inch gets there in only 7 to 8 inches.
How do I know which climate zone I am in?
The IECC numbers zones 1 through 8 from hottest to coldest, and your zone is set by county, so one state can span more than one zone. Look up your county on the IECC climate-zone map, then read the recommended R-value off the table above.
What are the signs that my home is under-insulated?
Rooms that run colder or hotter than the rest of the house, cold floors, drafts, and a ceiling that feels cold in winter all point to heat moving through the surface too easily. In snowy climates, ice dams at the eaves and higher-than-normal heating and cooling bills are common tells.