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How much attic insulation do I need?
Pick your county and measure what's up there now. The target comes from ENERGY STAR's table for your climate zone, and the bag count comes from the maker's own coverage chart, not a guess.
Before you add any
- Air seal first
"EPA recommends air sealing the attic before adding attic insulation."
- Recessed lights and soffit vents
"Never lay insulation over recessed light fixtures or soffit vents. Keep all insulation at least 3 inches away from recessed "can" lights, unless they are rated IC (Insulated Ceiling)."
- Flues and chimneys
"Because the pipe gets hot, building codes usually require 1 inch of clearance from metal flues (2 inches from masonry chimneys) to any combustible material, including insulation."
- Gas or oil appliances
"Sealing in some cases can cause naturally venting combustion appliances to back-draft gases back into your home, creating unsafe conditions."
ENERGY STAR suggests a Home Performance Contractor test them before and after sealing. - Vermiculite
"Do not disturb vermiculite insulation unless you have had it tested by an approved lab to be sure that it does not contain asbestos."
- Call a pro first if you find
Wet or damp insulation, moldy or rotted rafters or joists, kitchen, bath or dryer vents that exhaust into the attic, little or no attic ventilation, or "Knob and tube wiring (pre-1930), which can be a fire hazard when in contact with insulation."
- Where you step
"Walk on joists or truss chords, not exposed ceiling drywall or insulation, to avoid falling through the ceiling."
Source: ENERGY STAR, Attic Insulation Project and Attic Air Sealing Project. Retrieved October 30, 2026.
Products and bag counts
Every number comes from the maker's own coverage chart or data sheet. If a maker doesn't publish a number, the card says so instead of guessing.
The "check price" buttons are affiliate links.
Blown-in (loose fill)
Bags for your attic at each maker's chart row that covers the R-value you need. Contractor products are here so you can check the bag count on a quote: makers say the installer must put in at least the chart's bags and depth.
Batts and rolls
Over existing insulation, use unfaced batts. ENERGY STAR: "If you use fiberglass over loose fill, make sure the fiberglass batt has no paper or foil backing; it needs to be "unfaced."" Lay the new layer across the joists.
Where the numbers come from
1. The target
ENERGY STAR's table of recommended insulation levels for existing homes gives two attic columns: one for an attic with no insulation, and one for an attic that already has 3–4 inches. The tool takes the no-insulation column as the total to reach, then subtracts what you have. ENERGY STAR notes the table is based on the 2021 International Energy Conservation Code.
Source: ENERGY STAR, Recommended Home Insulation R-Values. Retrieved October 30, 2026. ENERGY STAR's DIY-checks page still shows an older range table (for example R38 to R60 in zone 4); the tool uses the newer one.
2. What you have
ENERGY STAR's method: "Either read the R-value printed on the batts of your existing insulation or use a measuring tape to measure the depth of the insulation (inches)." Then multiply the depth by the number for that material (table at right).
Source: ENERGY STAR, What to Look For: DIY Checks and Inspections. Retrieved October 30, 2026.
3. Your climate zone
From Pacific Northwest National Laboratory's county list for the 2021 IECC, prepared for the U.S. Department of Energy: 3,141 counties and county equivalents. Puerto Rico has no zone in that file, so it isn't in the list.
Source: PNNL-33270, Guide to Determining Climate Zones by County (2022) and its county data files. Retrieved October 30, 2026.
4. Bags and depth
Each maker's coverage chart lists, for each R-value, the minimum bags per 1,000 sq ft, the most square feet one bag may cover, and the minimum thickness. The tool takes the smallest chart row that covers the R-value you need (it never estimates between rows), meets both bag limits, and rounds up to whole bags.
Questions
What R-value insulation do I need in my attic?
For an attic with no insulation, ENERGY STAR's table says R30 in zone 1, R49 in zones 2 and 3, and R60 in zones 4 through 8. With 3–4 inches already there, it says add R25, R38 or R49 for those zones.
How do I find the R-value of what I already have?
Read the R-value printed on the batts, or measure the depth and multiply: loose fiberglass 2.5, loose rock wool 2.8, loose cellulose 3.7, vermiculite or perlite 2.7, fiberglass batts 3.2. Those are ENERGY STAR's numbers.
How many inches of blown-in is R-60?
It depends on the product, so use the maker's chart. Owens Corning AttiCat: 20.5 inches. Johns Manville Attic Protector: 22.6 inches installed, settling to 22.5. Greenfiber SANCTUARY cellulose: 17.3 inches installed, settling to 16.1.
Can I put new insulation on top of old?
Yes. ENERGY STAR: you don't have to use the same type, and you can add loose fill on top of fiberglass batts or blankets, and vice versa. Batts laid over loose fill must be unfaced, with no paper or foil backing.
Do I really need more?
ENERGY STAR's quick check: if the insulation is level with or below the attic floor joists, you probably need more. If you can't see any joists because the insulation is well above them, you probably have enough, and adding more may not be cost-effective.
| Zone | If your attic is uninsulated | If you already have 3–4 inches |
|---|
| What you see | What it probably is | R per inch |
|---|