Insulation R-Value Depth Chart: How Many Inches for R-30, R-49, R-60

Look up settled inches and bags per 1,000 sq ft for blown cellulose and fiberglass — by R-value target, brand, and DOE climate zone. Includes a reverse lookup so you can convert existing attic depth to current R-value.

Blown Insulation Depth Chart — Bags per 1,000 Sq Ft by Brand

The table below is the master reference for blown loose-fill attic insulation. Columns show all three major brands available at Home Depot and Lowe's. Rows show common R-value targets from R-13 (minimum Zone 1 top-up) through R-60 (DOE target for Zones 5–8). All depths reflect settled installed thickness as required by the FTC R-Value Rule 16 CFR Part 460 ↗.

Bag counts per 1,000 sq ft at the R-value shown (settled depth). SANCTUARY and SANCTUARY DEFENSE share the identical loose-fill chart per Greenfiber SANCTUARY Rev K 05/26 — both 25 lb bags, ~R-3.7 per inch (settled), same bag counts at every R-tier. AttiCat fiberglass uses significantly fewer bags because each bag weighs 27.5 lb and covers more area per unit weight at lower R-per-inch density.

Data current as of 2026. Manufacturer coverage charts are updated periodically — always verify against the chart printed on your specific bag before finalizing your purchase order.

How the R-Value Depth Math Works

Reverse lookup (existing depth → current R): Use the same formula backwards. If you have 8 inches of existing blown cellulose (SANCTUARY), your current R ≈ 8 × ~3.7 = R-29. If you have 8 inches of blown fiberglass, your current R ≈ 8 × 2.79 = R-22. The product difference alone (cellulose vs fiberglass at the same depth) is worth approximately 7 R-units — which is why measuring depth without knowing the product gives you an incomplete picture.

Why R-per-inch varies across the table: minor density variation is normal as depth increases — the weight-per-bag is fixed while air compresses slightly at the base. Values use the published per-R-level thickness (matches FTC coverage charts) rather than a constant R/inch.

Settling is already factored in. The FTC R-Value Rule (16 CFR Part 460 ↗) requires all manufacturer coverage charts to use settled thickness, not initial installed thickness. SANCTUARY cellulose settles ~7% per current Greenfiber chart in thickness within 48–72 hours per Greenfiber SANCTUARY Rev K 05/26 (vs the historical ASTM C-739 15–20% range), but the R-value per inch does NOT change when thickness decreases — only total thickness shrinks. The bag label already accounts for this: if the label says R-30 at 8.3 inches settled, 8.3 inches is the settled depth you'll retain after settling is complete.

Cellulose vs Fiberglass: R-Per-Inch Comparison and Depth Penalty

The single most important number for planning attic insulation is R-per-inch. Cellulose delivers more R per inch than blown fiberglass, which means you need shallower depth for the same R-value. At R-49, the depth difference is 3.7 inches — which is significant near the eaves where 2×6 or 2×8 rafters give you only 5.5–7.25 inches of clearance above any existing insulation.

Generic ranges per DOE energy.gov "Types of Insulation"; rock wool per NAIMA. Bag coverage chart is always authoritative for your specific product.

The ~0.9 R/inch gap = a 3.7-inch cellulose headroom advantage at R-49 and 4.4 in at R-60 — critical near low eaves in ranches/Cape Cods.

Reverse lookup: 10 in unknown blown = ~R-37 (SANCTUARY cellulose) or ~R-28 (fiberglass). Either way, Zone 5's R-60 target leaves 23–32 R-points to add. Use the blown-in R-value calculator for estimated additional inches and bags.

Air sealing often improves performance more than adding R-value when major bypasses exist. Unsealed top plates, electrical penetrations, and recessed-light gaps allow convection that bypasses insulation, cutting effective R 15–30%. Air-seal before blowing — always — particularly for cellulose (permeable, unlike spray foam).

Brand Comparison: Bags per 1,000 Sq Ft at R-30, R-38, R-49, R-60

All three brands at the four most common DOE-target R-values. SANCTUARY (25 lb) and SANCTUARY DEFENSE (25 lb) share the identical loose-fill chart; bag counts match at every R-tier. AttiCat is fiberglass — fewer bags, lower R/in, more depth. For 1,500 sq ft at Zone 5 R-49: ~106 bags SANCTUARY, ~106 bags SANCTUARY DEFENSE, or 38 bags AttiCat (10% buffer).

Sources: Greenfiber SANCTUARY Rev K 05/26 (38.6 bags at R-30 × 70.8 bags at R-49 × 86.0 bags at R-60); SANCTUARY DEFENSE Rev C 12/25 (identical chart); OC AttiCat TDS (14.6 × 25.0 × 31.5). All at 1,000 sq ft. Add 10% for attic irregularities.

At R-49 SANCTUARY and SANCTUARY DEFENSE match (70.8 bags) — identical loose-fill coverage chart. DEFENSE adds fire/insect-resistance branding; thermal/coverage values are equivalent. See our cellulose insulation guide and blown-in insulation guide for blower rental and dense-pack.

How Blown-In Compares to Spray Foam and Rigid Foam

When headroom is limited or you're converting to an unvented assembly, compare blown-in to spray foam and rigid foam: blown SANCTUARY cellulose delivers ~R-3.7 per inch (settled) (per SANCTUARY Rev K 05/26); blown fiberglass ~2.5–2.9 R/inch (ASTM C687); open-cell spray foam ~3.5–3.7 R/inch at $1.50–$3.50/sq ft installed; closed-cell spray foam ~6.0–7.0 R/inch at $3–6/sq ft+; rigid foam board (polyiso/XPS) ~4.0–6.5 R/inch. For an open attic floor, blown-in loose-fill is almost always the lowest cost per R-point. Spray foam is better suited to cathedral ceilings, unvented attic assemblies, or situations where R-value must be added without increasing depth (e.g., a 2×6 rafter cavity at R-19 batt where spray foam adds R-12 without deepening the assembly).

Cost Comparison — Per R-Value-Square-Foot by Brand (2026)

Material cost per R-value-square-foot (also called "cost per R-sqft") normalizes cost across products with different bag sizes, weights, and prices. At R-30 over 1,000 sq ft, Greenfiber SANCTUARY and AttiCat cost approximately the same per R-sqft — but at R-49 and R-60 (the DOE Zone 5–8 target), cellulose is significantly more cost-effective.

Cost estimates are approximate as of 2026; verify locally and add 10% bag buffer. Using a different brand? Derive R/in from the bag's coverage chart: R/in = labeled R ÷ minimum settled depth (in); sqft/bag = listed coverage at your target R.

Cellulose remains comparable or slightly less expensive per square foot at the same R-value once you account for current Greenfiber SANCTUARY (25 lb) bag pricing. For Zone 5–8 homeowners needing R-60, the cellulose cost picture is roughly even with AttiCat: approximately $1,200–$1,548 vs $1,260–1,575 for 1,000 sq ft in materials alone.

Rule of thumb: To hit R-49 over 1,000 sq ft, budget roughly $991–$1,275 in cellulose (Greenfiber SANCTUARY at ~$14–$18/bag × 70.8 bags per SANCTUARY Rev K 05/26) vs $1,000–$1,250 in AttiCat fiberglass (~$40–$50/bag × 25 bags). Costs are roughly comparable for high-R targets with current SANCTUARY 25 lb bag pricing. Both estimates exclude blower rental (free with qualifying bag purchase) and air-sealing materials.

DOE + ENERGY STAR Targets by Climate Zone — In Inches

The DOE publishes R-value targets by climate zone for cost-effective energy retrofits. The table below translates those R-targets to the exact installed depth required for each brand — so you can directly compare your attic's current depth to what you need. Targets are for the uninsulated attic scenario (starting from zero). For existing partial insulation, use the blown-in R-value calculator to input your current depth and get the additional inches needed.

How to find your climate zone: Enter your ZIP code at energystar.gov ↗ or view the DOE zone map at energy.gov ↗. County-level zone assignments also appear on most local building department websites.

These are DOE cost-effectiveness targets for retrofitting existing homes — not prescriptive code minimums. Local jurisdictions adopt different IECC editions (2018 vs 2021 vs 2024) with potentially different R-minimums. Zone 4A (humid) and 4C (marine Pacific NW) have different code requirements than Zone 4B (dry). Confirm current minimum R-values and any permit requirements with your local building department before starting. Requirements vary by jurisdiction and the specific IECC edition adopted locally.

How to Measure Your Existing Attic Insulation Depth

Before buying any insulation, measure what you currently have. Buying the wrong amount — either too little or too much — is the most common and avoidable mistake. Here are the exact steps:

1. Find your DOE climate zone — Use your ZIP code at energystar.gov ↗. Your zone determines your target R-value (R-30 in Zone 1, R-49 in Zones 2–4, R-60 in Zones 5–8).
2. Identify your current insulation type — Look at the texture. Blown cellulose is gray-brown, fibrous, looks like shredded newspaper. Blown fiberglass is pink, yellow, or white and looks fluffy. Fiberglass batts are flat mats with visible paper or foil facing. Knowing the type is essential for the reverse R-per-inch lookup.
3. Measure depth at multiple points — Use a ruler or tape measure. Take 5–6 measurements across the attic floor (not just near the hatch where insulation is sometimes disturbed). Average the readings. Existing insulation often settles unevenly, particularly near the eaves.
4. Calculate current R-value — Multiply your average depth by R-per-inch: SANCTUARY cellulose ≈ ~R-3.7 per inch (settled); fiberglass batts ≈ 3.14 R/in; blown fiberglass ≈ 2.79 R/in. Example: 8 inches of blown SANCTUARY cellulose = ~R-29.
5. Calculate the gap — Subtract current R from target R: e.g., R-60 target minus R-29 current = R-31 gap. Then: R-31 gap ÷ ~3.7 R/in (SANCTUARY cellulose) = 8.4 additional inches needed.
6. Air-seal before blowing — Before buying bags, inspect for top-plate gaps, electrical penetrations, and recessed lights. Seal with low-expansion spray foam or fire-rated caulk. Skipping air sealing can reduce effective R-value 15–30% through convective bypass, regardless of how many bags you add.
7. Use the calculator for final bag count — Enter your attic area, current depth, product type, and target R into the blown-in R-value calculator. The calculator accounts for existing R and outputs estimated additional inches and bags needed.

Common Insulation Depth and R-Value Mistakes

These issues show up repeatedly in Reddit /r/Insulation threads and contractor callbacks — each causes a measurable shortfall in R-value or an avoidable second trip to the store.

• Depth-vs-R confusion — "I have 10 inches, so I'm good." Depth without product type is meaningless: 10 inches of SANCTUARY cellulose = ~R-37; 10 inches of blown fiberglass = ~R-28; 10 inches of fiberglass batts = ~R-31. Always identify the existing material before using depth as a proxy for R-value. This is the #1 cause of under-insulated attics that already appear visually "full."
• Forgetting that old cellulose settles — If your cellulose is more than 20 years old, the actual depth may be lower than when installed (Greenfiber's current SANCTUARY chart implies ~7% per current Greenfiber chart settling; the historical ASTM C-739 range is 15–20%). Measure today's actual depth, not the depth from installation records or contractor estimates. Old settled cellulose at 8 inches may have been installed to 10 inches and now delivers only ~R-29, not the installed-day rating.
• Skipping air sealing first — Blown insulation fills voids but does not seal air pathways. Unsealed top plates and recessed light housing gaps allow stack-effect convection that bypasses the insulation entirely, reducing effective R-value by 15–30% per CIMA guidance. Air seal before blowing — always.
• Buying bags from one brand's chart, installing another brand's bags — Greenfiber SANCTUARY and SANCTUARY DEFENSE share the identical loose-fill chart (38.6 bags/1,000 sqft at R-30 each). Mixing in a non-Greenfiber brand without recalculating coverage can leave you with significant shortages or over-purchases. Always verify the coverage chart on the specific bag you're purchasing.
• Not installing rafter baffles at eaves before blowing — At R-49 to R-60 (13.3–16.1 inches of settled SANCTUARY cellulose), blown insulation will extend into the eave cavity and block soffit vents without baffles. Blocked soffit vents raise attic summer temperatures 10–20°F, accelerating shingle wear and defeating the purpose of adding insulation. Install baffles at every eave bay before blowing.
• Mixing cellulose over fiberglass without checking compatibility — You can add cellulose over existing fiberglass batts, but you should verify vapor retarder requirements for your climate zone first. In cold zones (5–8) the vapor retarder belongs on the warm-in-winter side (typically the kraft facing on the batt, against the ceiling drywall); in warm-humid zones (1–3) retarders generally go nearer the exterior. Adding loose-fill over batts is fine if the existing retarder is correctly positioned — when uncertain, consult DOE energysaver.gov or your local building department.
• Over-compressing existing batts when blowing on top — Loose-fill applied at proper density does not crush typical 9.5-inch R-30 batts, but if you walk on the attic during install or pile insulation against the top of a paper-faced batt, you can compress it. A compressed batt loses R-value proportional to thickness loss (an R-30 batt squashed to 7 in delivers only ~R-22). Distribute foot-traffic across joists with planks; don't tamp loose-fill down on top of batts.

Common Questions

How many inches of blown insulation do I need for R-49?

Greenfiber SANCTUARY cellulose: 13.3 inches settled, 70.8 bags/1,000 sq ft (per SANCTUARY Rev K 05/26). Owens Corning AttiCat fiberglass: 17.0 inches, 25 bags/1,000 sq ft. All values per settled depth under FTC 16 CFR Part 460 ↗. No overfill buffer needed.

What is the R-value of 10 inches of blown cellulose insulation?

SANCTUARY cellulose: ~R-37 (~3.7 R/in (settled) × 10 in). SANCTUARY DEFENSE (25 lb bag): ~R-37 (identical chart). AttiCat fiberglass: ~R-28 (2.79 R/in × 10 in). Cellulose requires 3–4 fewer inches than fiberglass to reach the same R-value.

Does blown insulation settle and lose R-value over time?

Blown SANCTUARY cellulose settles ~7% per current Greenfiber chart in thickness (per Greenfiber SANCTUARY Rev K 05/26, vs the historical ASTM C-739 15–20% range) but R-value per inch does NOT change — manufacturer coverage charts already use settled depth per FTC 16 CFR Part 460. The label R-value is what you retain. AttiCat fiberglass does not settle.

What R-value do I need for my climate zone?

Zone 1 (FL, HI): R-30. Zones 2–3 (AZ, TX, GA): R-49. Zones 4–8 (DC north through AK): R-60. Find your zone at energystar.gov ↗. See the full zone-depth table above for settled inches by brand.

What is the difference in R-value per inch between cellulose and fiberglass?

Greenfiber SANCTUARY cellulose: ~R-3.7 per inch (settled). AttiCat fiberglass: 2.79 R/in. The ~0.9 R/in gap creates a 3.7-inch depth advantage for cellulose at R-49 — 13.3 in settled vs 17.0 in — significant near low eaves.

Estimates only — verify with your local building authority and a qualified contractor before construction. See our full disclaimer.