Thickness Needed
10.3" of Blown-In Cellulose
R-Value Added
R-38
Est. Cost
$836
Payback
3.6 yr
Roughly equals your home’s footprint
DOE/IECC 2021 recommended attic R-values
Leave blank to use DOE recommendation for your zone
10.3"
$836
78%
3.6 yr
| Type | R/in | Depth | Est. Cost |
|---|---|---|---|
| Fiberglass Batts | R-3.2 | 11.9" | $1140 |
| Blown-In Fiberglass | R-2.5 | 15.2" | $950 |
| Blown-In Cellulose | R-3.7 | 10.3" | $836 |
| Open-Cell Spray Foam | R-3.6 | 10.6" | $3040 |
| Closed-Cell Spray Foam | R-6.5 | 5.8" | $4560 |
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Inputs
Result
Additional R needed: 49 − 11 = 38. Depth: 38 / 3.7 = 10.27 inches. Bags: (1,000 / 40) × (38/30) = 31.7 → 32 bags. Cost: 1,000 × 38 × $0.022 = $836.
Inputs
Result
Additional R needed: 38 − 0 = 38. Depth: 38 / 3.7 = 10.27 inches. Bags: (1,500 / 40) × (38/30) = 47.5 → 48 bags. Cost: 1,500 × 38 × $0.022 = $1,254.
The DOE and IECC 2021 code recommend R-30 to R-60 for attics depending on your climate zone. Zones 1–3 (southern US) need R-30 to R-38, zones 4–5 need R-49, and zones 6–7 (northern US) need R-60. Most older homes have R-11 to R-19, leaving a significant gap.
| Climate Zone | States (examples) | Recommended R-Value | Cellulose Depth |
|---|---|---|---|
| Zone 1–2 | FL, TX, AZ, HI | R-30 to R-38 | 8–10" |
| Zone 3 | CA, GA, NC, SC | R-38 | 10–11" |
| Zone 4 | VA, TN, MO, NM | R-49 | 13–14" |
| Zone 5 | OH, PA, IL, CO | R-49 | 13–14" |
| Zone 6 | MI, MN, WI, MT | R-60 | 16–17" |
| Zone 7 | AK, northern MN | R-60 | 16–17" |
Blown-in cellulose (R-3.7/inch) is denser, fills gaps better, and costs less than blown fiberglass (R-2.5/inch). Cellulose needs 30% less depth to achieve the same R-value. However, fiberglass resists moisture better and does not settle as much over time.
| Material | R-Value/Inch | Depth for R-49 | Cost/Sq Ft | Settling |
|---|---|---|---|---|
| Blown cellulose | R-3.7 | 13.2" | $0.80–$1.20 | 15–20% |
| Blown fiberglass | R-2.5 | 19.6" | $1.00–$1.50 | 2–5% |
| Fiberglass batts | R-3.2 | 15.3" | $0.60–$1.00 | None |
| Open-cell spray foam | R-3.6 | 13.6" | $1.50–$2.50 | None |
| Closed-cell spray foam | R-6.5 | 7.5" | $2.50–$4.00 | None |
For a 1,000 sq ft attic going from R-11 to R-49 with cellulose: you need R-38 additional. At R-3.7/inch, that is 10.3 inches of depth. A typical bag of cellulose covers about 40 sq ft at R-30, so for R-38 you need about 32 bags for 1,000 sq ft.
Attic insulation typically pays for itself in 2–5 years through reduced heating and cooling costs. Going from R-11 to R-49 can save $150–$400 per year on energy bills. DIY blown cellulose costs $500–$800 for a 1,000 sq ft attic, yielding a 2–3 year payback.
| Upgrade Path | Material Cost (1,000 sq ft) | Annual Savings | Payback |
|---|---|---|---|
| R-0 to R-30 | $500–$700 | $250–$400 | 1.5–2.5 yr |
| R-11 to R-38 | $400–$600 | $150–$250 | 2–3 yr |
| R-11 to R-49 | $600–$900 | $175–$300 | 2.5–4 yr |
| R-19 to R-60 | $700–$1,100 | $125–$225 | 3.5–5 yr |
| R-30 to R-60 | $500–$800 | $50–$100 | 5–8 yr |
Yes, in most cases you can add new insulation directly over existing insulation. Blown cellulose or fiberglass goes right on top. Do not add a vapor barrier between layers. However, if old insulation is wet, moldy, or vermiculite (may contain asbestos), remove it first.
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Last Updated: Oct 19, 2026
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