How it works
Attic insulation is priced by how much you add, so the calculator starts from the R-value you want to reach. ENERGY STAR recommends a total of R-30 to R-60 depending on your climate zone, less if you are topping up an attic that already has 3 to 4 inches.
The R-value you need to add, divided by your material's R-value per inch, gives the depth. Depth × area × the installed price per inch per square foot gives the cost. Blown-in cellulose and fiberglass are the cheapest per R-value; closed-cell spray foam has the highest R per inch but costs several times more.
Heat loss through a ceiling falls in proportion to 1 ÷ R, so going from R-11 to R-49 cuts heat flow through the ceiling by about three-quarters. The first few inches do the most; each extra inch saves less. Sealing air leaks around lights, pipes and the attic hatch first is usually the best-value step.
Default prices are 2026 US planning figures for professional installation. Replace them with a quote for your home.
The formula
R to add = target R − current R inches needed = R to add ÷ R per inch material cost = area × inches × price per inch per sq ft heat flow cut = 1 − current R ÷ target R
Worked example
A 1,000 sq ft attic in climate zone 5 with about 3.5 inches of old insulation (R-11), topped up to R-49 with blown-in cellulose (R-3.7 per inch, about $0.16 per inch per sq ft) plus air sealing.
| Step | Working | Result |
|---|---|---|
| R-value to add | 49 − 11 | R-38 |
| Depth | 38 ÷ 3.7 | 10.3 in |
| Insulation | 1,000 × 10.27 × $0.16 | $1,643 |
| Air sealing | allowance | $600 |
| Total | $2,243 | |
| Heat flow through the ceiling | 1 − 11 ÷ 49 | 77.6% less |
Recommended attic R-values
| Climate zone | Uninsulated attic | Adding to 3–4 in |
|---|---|---|
| Zone 1: South Florida, Hawaii | R-30 | R-25 |
| Zone 2: Gulf Coast, Southern Texas, Arizona low desert | R-49 | R-38 |
| Zone 3: Southeast, Southern California, Southwest | R-49 | R-38 |
| Zone 4: Mid-Atlantic, Pacific Northwest coast, Kentucky | R-60 | R-49 |
| Zone 5: Midwest, Northeast, Colorado | R-60 | R-49 |
| Zone 6: Upper Midwest, Northern New England, Montana | R-60 | R-49 |
| Zone 7: Northern Minnesota, Wisconsin, mountains; most of Canada | R-60 | R-49 |
| Zone 8: Alaska interior, northern Canada | R-60 | R-49 |
Frequently asked questions
How much does it cost to insulate a 1,000 sq ft attic?
Roughly $2,200 to top up R-11 to R-49 with blown-in cellulose including air sealing, using 2026 US planning prices. Blown fiberglass is similar; closed-cell spray foam can cost five to ten times more.
How many inches of insulation do I need for R-49?
About 13.2 inches of blown cellulose, 19.6 inches of blown fiberglass or 15.8 inches of fiberglass batts, starting from a bare attic.
Is blown-in or batt insulation cheaper?
Blown-in is usually cheaper and fills gaps around joists and wiring better. Batts are easier for a DIY job in an open attic with standard joist spacing.
Should I remove old insulation first?
Only if it is wet, mouldy, contaminated by pests, or you need to air seal underneath it. Otherwise new insulation can go on top. Old vermiculite (grey-brown, pebble-like) may contain asbestos and should be tested before it is disturbed.
Is attic insulation worth it?
It is one of the cheapest energy upgrades when the attic has less than about R-30, especially combined with air sealing. If you already have R-38 or more, extra inches save little.
Sources
- ENERGY STAR, recommended home insulation R-values.
- US Department of Energy, types of insulation (R-value per inch).
- Installed prices: 2026 US planning ranges for professional installation; get a local quote.
Related guides
Estimates are for planning only and are not financial advice. Get written quotes before you buy.