Cellulose Insulation Thickness Chart by R-Value

Find the settled depth in inches you need for R-30, R-38, R-49, and R-60 across Greenfiber's two main cellulose product lines — SANCTUARY and SANCTUARY DEFENSE — plus an AttiCat fiberglass comparison. Includes the Greenfiber SANCTUARY Rev K 05/26 settling math and the initial-vs-settled depth distinction required by the FTC R-Value Rule.

Cellulose Insulation Depth Chart by R-Value and Brand

The table below shows settled depth (post-settling, R-value-equivalent) at four common attic targets. Data derived from manufacturer technical data sheets (TDS) using Greenfiber SANCTUARY Rev K 05/26 settling math (@asOf 2026-06-02 (verified)). Verify bag label coverage chart before installing — TDS values represent typical lab conditions; field settling may vary ±5%.

Sources: Greenfiber SANCTUARY and SANCTUARY DEFENSE Technical Data Sheets; Owens Corning AttiCat TDS (R/in 2.79 — already validated on /blown-in-r-value-calculator/). Settled depth values from Greenfiber SANCTUARY / SANCTUARY DEFENSE TDS (Greenfiber SANCTUARY Rev K 05/26) settling math @asOf 2026-06-02 (verified). AttiCat depth shown for comparison only — see AttiCat guide for full AttiCat coverage data.

How Cellulose Depth Is Calculated

Cellulose insulation depth is a direct function of the product's R-value per inch (R/in) rating. Because loose-fill cellulose has a consistent R/in (~3.7 R/in (settled) per Greenfiber SANCTUARY Rev K 05/26) across installed depths, the formula is straightforward:

Cellulose depth formula:

  depth (inches) = R-target / R-per-inch

  Where:
    R-target    = the settled R-value you want to achieve
    R-per-inch  = brand-specific settled R-value per inch (from TDS)

  --- Worked example: R-49 target with Greenfiber SANCTUARY ---

  R-per-inch (SANCTUARY at R-49)  = 3.684  (derived per SANCTUARY Rev K 05/26)
  R-target                        = 49

  depth = 49 / 3.684
        = 13.30 inches (settled depth, per chart)

  Initial install depth (Greenfiber SANCTUARY Rev K 05/26, ~7% per current Greenfiber chart settling):
    14.3 inches initial → 13.3 in settled at R-49 (chart row)

  → Blow to 14.3 inches initially to settle at ~13.3 in target depth.

  --- SANCTUARY DEFENSE comparison at R-49 ---

  R-per-inch (SANCTUARY DEFENSE at R-49) = 3.684 (identical chart)
  depth = 49 / 3.684 = 13.30 inches ≈ 13.3 inches (settled)

  → At R-49, SANCTUARY DEFENSE matches SANCTUARY: same settled depth (13.3 in)
    and same bag count (70.8 bags per 1,000 sqft). DEFENSE differs only on
    fire/insect-resistance branding; thermal/coverage values are equivalent.

The FTC R-Value Rule (16 CFR Part 460) requires manufacturers to include a coverage chart on every bag showing the minimum initial thickness and settled thickness required to achieve labeled R-values at specific bag counts per 1,000 sqft. The bag label is the authoritative spec for that production run — field R/in can vary slightly from the nominal TDS value due to moisture content and machine calibration.

The Greenfiber SANCTUARY / SANCTUARY DEFENSE TDS (Greenfiber SANCTUARY Rev K 05/26) standardizes the test methodology for settling measurement. SANCTUARY cellulose settles ~7% per current Greenfiber chart from initial install depth; fiberglass blown-in (e.g., AttiCat) settles approximately 0% — which is why AttiCat needs no settling adjustment but requires more initial depth to achieve the same R-value due to its lower R/in of 2.79.

Settled Depth vs Initial Depth: FTC Rule and Greenfiber SANCTUARY Rev K Explained

1. Why Settled Depth Is the R-Value-Relevant Measurement

When cellulose is first blown into an attic, it is fluffed and at maximum volume. Over weeks to months, the fibers compress under their own weight — a process governed by Greenfiber SANCTUARY / SANCTUARY DEFENSE TDS (Greenfiber SANCTUARY Rev K 05/26) settling mechanics. The settled depth is the stable, long-term depth at which the insulation delivers its rated R-value per inch. Installing to settled depth immediately would under-deliver because the insulation hasn't been given room to compress naturally — you blow deeper than target and let physics settle it to spec.

The FTC R-Value Rule (16 CFR Part 460 §460.5) requires every bag to display the minimum initial thickness (at install) and minimum settled thickness (post-settling) needed to achieve the labeled R-value. This disclosure is mandatory — not optional marketing. Always use the settled thickness column from the bag label to verify you hit your R-target; do not measure immediately after installation and claim success.

2. Settling Factor by Product: ~7% for New Installs (Greenfiber SANCTUARY Rev K 05/26)

Standard cellulose settling per Greenfiber SANCTUARY / SANCTUARY DEFENSE TDS (Greenfiber SANCTUARY Rev K 05/26) is ~7% per current Greenfiber chart by depth for new attic installations. Greenfiber SANCTUARY (25 lb bag) and SANCTUARY DEFENSE (25 lb bag) share the identical loose-fill coverage chart (~R-3.7 per inch (settled)); DEFENSE adds fire/insect-resistance branding only, with no thermal/coverage difference.

Top-up installs (adding to existing settled cellulose) behave differently. When new cellulose is blown over a settled base layer, the old layer provides compression support — the new layer settles at approximately 5–7% rather than the full ~7% per current Greenfiber chart. Apply the 5–7% settling factor when planning a depth top-up; using a higher factor will cause you to over-blow by 0.5–1 inch at R-49 depth ranges.

3. How to Measure Settled Depth Accurately

After installation, insert a calibrated depth ruler or depth rod straight down through the cellulose to the attic floor deck — not to the top of any existing layer. Measure at three to five points across the attic and average the readings. Most building inspectors require depth markers (typically 1-foot ruled stakes) installed in the attic to document settled depth. The ENERGY STAR Insulation Methodology recommends measuring at least every 100 sqft for large attics.

Brand Comparison: Greenfiber SANCTUARY vs SANCTUARY DEFENSE vs AttiCat

The table below compares key specs across Greenfiber's two cellulose product lines and AttiCat fiberglass (for reference). Data from manufacturer TDS @asOf 2026-06-02 (verified) and validated against ENERGY STAR Insulation R-Value Recommendations. Verify bag label before purchase — coverage specs can change between production runs.

Affiliate disclosure: CraftedCalcs earns commission on purchases made through the Home Depot and Amazon links below. The commission doesn't change your price. It helps us keep this site free.

R/inch data from Greenfiber SANCTUARY / SANCTUARY DEFENSE TDS @asOf 2026-06-02 (verified). AttiCat R/in 2.79 from Owens Corning TDS (HIGH confidence, validated on /blown-in-r-value-calculator/). Brand names referenced for descriptive purposes (nominative fair use). Greenfiber® is a trademark of US GreenFiber LLC. Owens Corning® and AttiCat® are trademarks of Owens Corning. CraftedCalcs is not affiliated with or endorsed by these manufacturers.

Cellulose Insulation Cost Estimate — 2026-Q2 Reference

Bag pricing varies by retailer, region, and product tier. The ranges below are from Home Depot and Amazon retail listings (@asOf 2026-Q2) — verify at retailer before purchase. Per-project estimates use R-49 / 1,000 sqft as the basis; scale bag count from the reference table above.

Prices as of 2026-Q2; verify at retailer before purchase — pricing changes seasonally and varies by region. Blower rental (typically $0 with minimum bag purchase at Home Depot) and labor (DIY vs contractor) are not included. Use the Cellulose Insulation Calculator to estimate bag count for your specific attic area.

DOE Climate Zones and Target R-Values

The correct R-value target for your attic depends on your DOE climate zone. The ENERGY STAR Insulation R-Value Recommendations provide zone-specific targets: R-30 for zones 1–3 (southern climates), R-38 for zone 4, R-49 for zones 5–7 (most of the continental US), and R-60 for zone 8 (arctic/subarctic). Translating to cellulose depth using SANCTUARY (settled): R-30 ≈ 8.3 in, R-38 ≈ 10.4 in, R-49 ≈ 13.3 in, R-60 ≈ 16.1 in. Verify your zone at the DOE zone map before selecting a target — zones 4 and 5 border regions are the most common source of confusion. Sub-zone resolution matters: 4A (humid), 4B (dry), and 4C (marine/Pacific NW) share the R-38 baseline but differ on vapor-retarder placement and air-sealing emphasis. IECC 2021 codifies the same zone map adopted by most state amendments; jurisdictions on IECC 2018 may still target R-38 in zone 5 (IECC 2021 raised this to R-49 in some climates). California Title 24 and a handful of state amendments (NY, MA, OR) override DOE zone targets — check your local building department for the adopted IECC edition before purchasing.

Cellulose Depth Checklist: Before and During Installation

These 6 steps prevent the most common cellulose depth errors on attic insulation projects (R-49 typical target = ~13.3 in settled SANCTUARY). All are pre-install decisions — correcting depth shortfalls after the blower is returned is expensive.

1. Confirm your DOE climate zone and corresponding R-target before buying bags. A zone 5 homeowner targeting R-38 instead of R-49 will under-insulate by ~2.9 inches of settled SANCTUARY cellulose and lose significant heating-season performance.
2. Read the coverage chart on the bag label — use the settled thickness column. The FTC R-Value Rule requires this data on every bag. The settled thickness column tells you the long-term R-value-equivalent depth. Do not use the initial thickness column to assess completion.
3. Estimate your initial install depth by applying the settling factor. Divide settled target depth by (1 − settling fraction): e.g., 13.3 in / 0.93 ≈ 14.3 in initial depth (at ~7% per current Greenfiber chart settling). Set depth rods or chalk marks at the initial target — not the settled target.
4. Install depth rods or ruler stakes before blowing. Place marked stakes every 100–150 sqft so you can visually confirm coverage depth as you blow. Remove and re-measure after a 4-week settling period to confirm settled depth meets your R-target.
5. Air-seal all attic penetrations before blowing cellulose. Cellulose is air-permeable when loose-fill; unsealed recessed lights, top plates, and wiring chases allow stack-effect air to reduce effective R-value by 10–15% per industry practice. Air-sealing is a separate scope from insulation depth and must be completed first.
6. Use the 5–7% settling factor (not the full ~7% per current Greenfiber chart) when calculating top-up depth. If adding to settled cellulose, the old layer provides support. Over-applying the new-install factor to a top-up will overshoot by 0.5–1 inch, adding unnecessary material cost.

Common Cellulose Insulation Depth Mistakes

These five errors account for most cellulose depth shortfalls, sourced from r/Insulation and r/HomeImprovement installer threads. Each is preventable at the planning stage.

• Measuring initial depth instead of settled depth. Blowing to the settled target depth immediately — and then measuring right away — reads as success. But if you installed to 13.3 in (settled target) without the ~7% per current Greenfiber chart initial overshoot, the insulation will settle to roughly 12.4 inches and your final R-value will be R-45 to R-46, not R-49. Per Greenfiber SANCTUARY / SANCTUARY DEFENSE TDS (Greenfiber SANCTUARY Rev K 05/26), always blow to the initial depth from the bag label and measure settled depth after 4+ weeks.
• Topping up old cellulose using the full new-install settling factor. New cellulose blown over a settled base compresses at 5–7%, not the full ~7% per current Greenfiber chart. Using the full factor causes over-blowing of 0.5–1 inch at R-49 depth ranges, adding 3–5 extra bags per 1,000 sqft of unnecessary material cost.
• Mixing cellulose brands mid-job. SANCTUARY and SANCTUARY DEFENSE share the identical Greenfiber chart (~R-3.7 per inch (settled)). Switching to a non-Greenfiber brand mid-attic without recalculating coverage creates uneven zones — some areas may fall short of target R-value and others will exceed it. The total R-value becomes hard to verify from bag count alone.
• Skipping air-sealing before blowing. Cellulose's loose-fill structure means stack-effect air can short-circuit through unsealed penetrations. Industry practice identifies 10–15% effective R-loss in attics without proper air-sealing before blown insulation. Air-sealing recessed lights, top plates, and wiring chases is the single highest-ROI step before adding cellulose depth.
• Assuming all Greenfiber bags are the same product. SANCTUARY (25 lb, loose-fill) and SANCTUARY DEFENSE (25 lb, loose-fill, fire/insect resistance) share the identical loose-fill chart and deliver the same depth/bag-count at every R-tier (70.8 bags per 1,000 sqft at R-49). Greenfiber also sells dense-pack SKUs — those use different coverage charts and are not interchangeable with loose-fill attic projects. Always match the coverage chart to the specific product code on the bag.

Frequently Asked Questions

Estimates and specifications in this guide are for informational purposes only. Verify all depth values against the bag label coverage chart and confirm with your installer before purchasing. See our full disclaimer.