Attic Insulation R-Value: How Much Do You Need?
R-value measures how well insulation resists heat flow. Here's what ENERGY STAR recommends for attics in each climate zone and how to tell how close your attic is.
Most of the U.S.
R-49 to R-60
ENERGY STAR's recommendation for uninsulated attics in climate zones 4 through 8, which cover most of the country north of the Sun Belt.1
Recommended attic R-values by climate zone
| Climate zone | Uninsulated attic | Adding to 3–4 in. existing |
|---|---|---|
| Zone 1 (south Florida, Hawaii) | R-30 to R-49 | R-25 to R-30 |
| Zones 2–3 (Gulf Coast, Southwest, much of the South) | R-30 to R-60 | R-25 to R-38 |
| Zones 4–8 (Mid-Atlantic, Midwest, Mountain West, North) | R-49 to R-60 | R-38 to R-49 |
Source: ENERGY STAR's recommended home insulation R-values.1 Your local energy code may set a specific minimum for new construction, and utility rebate programs often require a particular finished R-value.
Which zone are you in?
Rough guide for the metros we cover: Phoenix, Las Vegas, San Antonio and Austin are in the warm zones (2–3); Charlotte and Sacramento are in zone 3; Kansas City, St. Louis, Louisville, Philadelphia and Cincinnati are in zone 4; Indianapolis, Cleveland, Detroit, Grand Rapids, Boston and Rochester are in zone 5; Minneapolis is zone 6. ENERGY STAR's map shows exact county boundaries.1
How to check what you have
- Look safely. Open the hatch and look without walking on the insulation or ceiling drywall. Step only on joists, or stay on the hatch platform.
- Identify the material. Fluffy fiberglass (pink, yellow or white), gray cellulose, batts, or pebbly vermiculite. If it's vermiculite, stop: EPA advises leaving it undisturbed.4
- Measure depth. Push a ruler gently to the drywall in a few spots.
- Estimate R-value. Loose-fill fiberglass and cellulose run very roughly R-2.2 to R-3.8 per inch depending on product and density. Your installer should use the manufacturer's coverage chart on the bag for exact depth.
Rule of thumb: if the insulation is level with or below the tops of your floor joists, you probably have less than R-30 and would benefit from adding more.
How many inches is R-49 or R-60?
It depends on the material. As a rough guide, R-49 is often in the range of 13 to 20 inches of blown-in insulation, and R-60 in the range of 16 to 24 inches. The bag's coverage chart lists the minimum settled thickness for each R-value, and many programs require depth markers so you can verify it.
What going from R-38 to R-49 or R-60 costs
HomeGuide's national figures for blown-in insulation are $1,100 to $1,900 per 1,000 square feet to reach R-49, and $1,400 to $2,400 to reach R-60.2 More detail in our attic insulation cost guide.3
More than R-value
- Air sealing stops warm air from carrying heat straight past insulation. Seal before you insulate.
- Ventilation baffles at the eaves keep insulation from blocking soffit vents.
- Hatch and pull-down stairs need their own insulated, weatherstripped cover.
- Recessed lights must be IC-rated (rated for insulation contact) or covered properly.
- Ducts in the attic should be sealed and insulated; they can waste more energy than thin insulation.
Common questions
What R-value should attic insulation be?
ENERGY STAR recommends R-49 to R-60 for uninsulated attics in climate zones 4–8, R-30 to R-60 in zones 2–3, and R-30 to R-49 in zone 1.
How many inches of insulation is R-49?
Roughly 13 to 20 inches of blown-in insulation, depending on the material. Check the coverage chart on the product for the exact settled depth.
Is R-60 worth it over R-49?
In cold zones 4–8, ENERGY STAR's recommendation goes up to R-60. HomeGuide's national cost to reach R-60 is $1,400 to $2,400 per 1,000 sq ft versus $1,100 to $1,900 for R-49.
Can I add new insulation on top of old?
Usually, if the old insulation is dry and not moldy or contaminated. Don't disturb vermiculite; EPA advises assuming it may contain asbestos.
Does attic insulation need air sealing?
Yes. Air sealing gaps around wiring, plumbing, lights and the hatch is what lets insulation perform as rated.
General information summarized from the public sources listed below. It isn't professional, medical or legal advice. A licensed professional who inspects your home can tell you what it needs.