The insulation target for most U.S. homes is R-49 to R-60 in the attic, fully insulated exterior walls, and R-19 to R-38 in floors above unheated spaces. The right amount depends on the home's U.S. climate zone, the area being insulated, and the insulation already in place.
For an existing home, start with the attic. ENERGY STAR recommends adding about R-30 to R-60, depending on climate zone and the current insulation level. The 2021 International Energy Conservation Code lists attic targets from R-30 in Zone 1 to R-60 in Zones 4 through 8.
Insulation Requirements at a Glance
| Area of the Home | Typical Target for an Existing U.S. Home | Important Considerations |
|---|---|---|
| Attic floor or ceiling | R-49 to R-60 in many regions | R-30 may be suitable in the warmest zones |
| Exterior walls | Fully filled wall cavities, often R-13 to R-20 or more | Wall assembly and exterior continuous insulation affect the result |
| Floor above a crawlspace or garage | R-19 to R-38 | Use insulation made for floors, not attic loose-fill |
| Basement or crawlspace walls | About R-13 to R-19 batt, or R-5 to R-15 rigid insulation | Moisture control and vapor management matter |
| Rim joists | Insulate and air-seal carefully | Spray foam and rigid foam are common options |
These are planning ranges. Local building codes may require different assemblies for new construction or major renovations.
How Much Attic Insulation Do I Need?
Attic insulation targets depend on the climate zone and the amount already installed.
| U.S. Climate Zone | If the Attic Is Uninsulated | If the Attic Has 3 to 4 Inches Already |
|---|---|---|
| Zone 1 | Add R-30 | Add R-25 |
| Zone 2 | Add R-49 | Add R-38 |
| Zone 3 | Add R-49 | Add R-38 |
| Zones 4A and 4B | Add R-60 | Add R-49 |
| Zones 4C, 5 and 6 | Add R-60 | Add R-49 |
| Zones 7 and 8 | Add R-60 | Add R-49 |
This table is based on ENERGY STAR retrofit recommendations for existing wood-framed homes.
How Can I Tell Whether I Need More Attic Insulation?
You may need more attic insulation if:
- The insulation is level with or below the attic joists.
- Large low spots or exposed areas are visible.
- Insulation is thin or uneven around the eaves.
- The ceiling feels unusually hot in summer or cold in winter.
- Heating and cooling costs remain high despite a properly sized HVAC system.
Measure the insulation depth and estimate its current R-value before adding more. ENERGY STAR lists these approximate R-values per inch:
- Loose-fill fiberglass: R-2.5
- Rock wool: R-2.8
- Cellulose: R-3.7
- Fiberglass batts: R-3.2
For example, 10 inches of cellulose provides about R-37 before accounting for settling, compression or installation quality.
How Much Wall Insulation Do I Need?
Wall insulation depends on the wall assembly, not only on the thickness of the insulation.
For an uninsulated 2-by-4 wood-frame wall, 2021 IECC guidance includes options such as:
- R-13 cavity insulation in warmer climate zones
- R-20 cavity insulation in many colder climate zones
- R-13 cavity insulation plus R-5 continuous exterior insulation
- R-13 cavity insulation plus R-10 continuous exterior insulation
- R-20 cavity insulation plus R-5 continuous exterior insulation
Continuous insulation is installed across the wall assembly, commonly behind the siding. It reduces heat flow through wood studs, which conduct more heat than insulated wall cavities.
In an existing home, contractors can often blow cellulose or fiberglass into empty wall cavities without removing all the interior drywall. Exterior rigid insulation is usually easier to add when the home is already being re-sided.
How Much Floor Insulation Do I Need?
For floors above an unheated crawlspace, basement, garage or outside area, ENERGY STAR recommends:
- R-13 in the warmest climate zones
- R-19 in moderate climates
- R-30 in colder climates
- R-38 in the coldest climate zones
The insulation should fit tightly between floor joists without gaps or compression. Before installing it, air-seal the floor perimeter, plumbing penetrations, wiring holes and rim joists. Insulation does not stop air movement through open cracks and gaps.
How Much Basement or Crawlspace Insulation Do I Need?
Basement and crawlspace wall targets vary by climate zone and insulation type:
- Zone 3: R-5 rigid insulation or R-13 batt insulation
- Zones 4A and 4B: R-10 rigid insulation or R-13 batt insulation
- Zones 4C through 8: R-15 rigid insulation or R-19 batt insulation
An unvented crawlspace also needs ground moisture control. The U.S. Department of Energy says exposed earth in an unvented crawlspace should be covered with a continuous vapor retarder and air barrier where required by applicable code.
How Do I Calculate How Much Insulation to Buy?
Use these four steps:
- Measure the area. Multiply length by width for an attic or floor. For walls, multiply wall height by wall length, then subtract doors and windows.
- Choose the target R-value. Use the climate zone and the location being insulated.
- Measure the existing insulation. Check the product label or estimate the current R-value from its depth and insulation type.
- Calculate the material needed. For batts and rolls, use the package coverage area. For blown-in insulation, use the manufacturer's bag-count chart.
Do not estimate blown-in insulation by inches alone. Cellulose, fiberglass and mineral wool have different R-values per inch, and loose-fill insulation must be installed at the correct density.
Should I Use Fiberglass, Cellulose or Spray Foam?
Choose the material based on the location and installation conditions:
- Blown-in cellulose: Often used on attic floors and in enclosed existing wall cavities
- Blown-in fiberglass: Suitable for attics and some wall cavities
- Fiberglass batts: Common in accessible wall, floor and ceiling cavities
- Mineral wool batts: Useful when fire resistance, sound control or moisture resistance is a concern
- Rigid foam board: Useful for continuous exterior insulation, basement walls and areas with limited space
- Spray foam: Useful around difficult air-sealing details and irregular cavities, but it needs careful installation and usually costs more
Seal air leaks before adding insulation. ENERGY STAR recommends sealing attic hatches, recessed lights, plumbing openings, dropped soffits and other penetrations before insulating the attic.
What Safety Checks Should I Make Before Adding Insulation?
Before installing insulation:
- Do not disturb loose vermiculite insulation until it has been tested. It may contain asbestos.
- Keep soffit vents open so the attic can ventilate.
- Maintain the required clearance around chimneys, flues and heat-producing fixtures.
- Use proper covers around older recessed lights where required.
- Do not compress batt insulation into spaces that are too small.
- Repair roof leaks before insulating.
- Remove wet, moldy or contaminated insulation.
ENERGY STAR recommends consulting a qualified energy professional if the home has vermiculite, unusual roof construction, moisture problems or inaccessible insulation cavities.
Where Should I Start?
Measure the insulation you have before buying more. If the attic falls below the target for your climate zone, seal air leaks first and then use the insulation manufacturer's coverage chart to calculate the required rolls, batts or bags. For walls, floors, basements and crawlspaces, use the wall assembly and local code requirements to set the target.