Blown-In R-Value Calculator
Enter your attic depth or target R-value to get the estimated depth and bag count for AttiCat fiberglass or Greenfiber cellulose blown-in insulation.
R-per-inch from manufacturer TDS (AttiCat: OC fact sheet 2019-Q4, last published version, ASTM C687; Greenfiber: Lowe's product guide DM-6.3-342 Rev A 2016-Q4, last published version). Settling per ASTM C739 §11.2 (cellulose: 15–20%; AttiCat: 0%). DOE + ENERGY STAR climate-zone targets. Always verify coverage against the chart printed on your specific bag — manufacturers may update specs. For professional installation, energy code compliance, or building permit applications, consult a licensed insulation contractor or your local building authority.
Quick Answer
For Zone 5 (cool-climate states including IL, OH, CO, and parts of PA — check your ZIP at energystar.gov) the DOE recommended range is R-49 to R-60 (this tool uses the conservative R-60 upper bound) and ENERGY STAR recommends R-60. The example below uses R-49 as an illustrative starting point — to reach R-60, add 3.5 more inches (AttiCat) or 3.2 more inches (cellulose). With AttiCat fiberglass, reaching R-49 requires 17.6" initial depth (17.6" settled) — about 31 bags for 1,200 sqft. Select your climate zone, brand, and attic size below for your estimated numbers. Jump to calculator →
CraftedCalcs — Blown-In Insulation R-Value Planning Reference
Generated: · Mode: Inverse · Brand: AttiCat · Attic: 1200 sqft
Cross-Section — Attic Blown-In Insulation: Initial vs Settled Depth
Schematic — not to scale. Settling applies to cellulose loose-fill per ASTM C739 §11.2 (15–20%). Owens Corning AttiCat fiberglass specs are settled values (0% additional settling). For planning estimates only.
Schematic — not to scale. Settling applies to cellulose per ASTM C739 §11.2 (15–20%). AttiCat specs are settled values. For planning estimates only.
Estimate your Blown-In Insulation
Quick scenarios:
Click any preset to fill the form, then adjust as needed.
Scope: assumes bare joists (new install or full tear-out). Topping up existing insulation? Use the Attic Insulation Calculator.
Your Insulation Estimate
PDF includes your inputs, results, bag chart, and the full compliance disclosure — planning aid only, not a permit document.
R-value (settled)
R-49
After 48–72 hr settling
Bags needed
31
From manufacturer chart
Initial depth
17.6"
Install to this depth
- R-value (initial — before settling)
- R-49
- Settled depth
- 17.6"
- R-value per inch (settled)
- 2.79
- Settling factor applied
- 0% (ASTM C739 §11.2)
- Sqft per bag (coverage chart)
- 39.9 sqft/bag
- Attic area
- 1,200 sqft
Climate Zone Targets
- DOE recommended
- R-60
- ENERGY STAR
- R-60
- Meets DOE target?
- —
- Meets ENERGY STAR?
- —
All zones reference (1–8)
| Zone | DOE | ENERGY STAR | Example cities |
|---|---|---|---|
| 1 | R-30–49 | R-30 | Miami, Honolulu |
| 2 | R-49–60 | R-49 | Houston, Orlando |
| 3 | R-49–60 | R-49 | Atlanta, Los Angeles |
| 4 | R-60 | R-60 | Nashville, DC |
| 5 | R-60 | R-60 | Chicago, Boston |
| 6 | R-60 | R-60 | Minneapolis, Burlington |
| 7 | R-60 | R-60 | Duluth, Bismarck |
| 8 | R-60 | R-60 | Fairbanks |
Sources: DOE energy.gov · ENERGY STAR (verified 2026-05-17; 2021 IECC). Cost-effectiveness retrofit targets — not prescriptive code minimums; local jurisdictions may use 2018 or 2024 IECC.
✓ What was checked
- ✓ R-per-inch from manufacturer TDS (AttiCat ASTM C687; Greenfiber Lowe's guide 2016-Q4)
- ✓ Settling factor per ASTM C739 §11.2 (cellulose: 15–20% midpoint 17.5%; AttiCat: 0%)
- ✓ Bag count from manufacturer coverage chart (matched to nearest R-value tier)
- ✓ DOE climate-zone targets (DOE energy.gov; 2021 IECC basis)
- ✓ ENERGY STAR targets (energystar.gov; 2021 IECC basis)
▼ Not checked / unverified provisions
- Greenfiber INS515LD + INS541LD data from 2016 product guide — verify against current bag label
- Generic cellulose uses R-3.2/in (FTC R-Value Rule baseline) — actual product may differ
- Cellulose settling varies with installed density, humidity, and attic conditions
- Air leakage / infiltration rates — not computed; air-seal BEFORE insulating
- Existing insulation R-value not deducted — this is the required TOTAL depth, not an add-on
Sources: ASTM C687 (AttiCat) · ASTM C739 §11.2 (cellulose settling) · FTC 16 CFR 460 (R-Value Rule) · DOE/ENERGY STAR (2021 IECC). Local amendments may apply — verify with your building authority before purchasing.
Need a quick depth reference? See the R-value vs depth quick reference table →
Full Materials Checklist
Complete materials for a blown-in attic insulation project. Quantities shown for 1,200 sqft at R-49 with AttiCat fiberglass — adjust for your attic size, target R-value, and selected brand.
Estimate only — not a professional bill of materials. It is NOT professional engineering, architectural, or contracting advice; NOT a code-compliance certificate; NOT a building permit application; and NOT a substitute for review by a licensed professional. Verify every quantity against your actual cut list, site conditions, and local building authority before purchasing. See our full disclaimer for details.
Insulation materials
- Qty: 31 bags for 1,200 sqft at R-49 (Zone 5) — adjust for your attic size and target R · AttiCat uses an expanding fiber system — coverage chart shows settled R-values (no additional settling adjustment needed). Verify bag count against the coverage chart on the bag. @source: AttiCat TDS PDF ASTM C687 (2019-Q4).
- Qty: See calculator above for your depth and attic size · Loose-fill cellulose; settles 15–20% after install per ASTM C739 §11.2. Calculator accounts for settling when you enter initial depth. Coverage chart from Lowe's product guide (2016-Q4) — verify against current bag label.
- Qty: See calculator above for your attic size · Smaller 19 lb bag — more convenient for solo DIY; more bags needed per sqft than the 30 lb INS515LD. Same product family, slightly lower R-per-inch (3.22 vs 3.33). Coverage chart from Lowe's product guide (2016-Q4).
Blowing equipment
- Qty: 1 machine — typically free with purchase of ≥10 bags at Home Depot or Lowe's · Home Depot and Lowe's both offer free blowing machine rental with qualifying bag purchase. Confirm current promotion at checkout. Machines have minimum bag requirements — typically 10+ bags.
- Qty: 1–2 extensions depending on attic depth · Longer hose lets you stay at the attic hatch while blowing to far corners. Most rental machines include a hose — verify length against your longest attic run.
Safety and prep
- Qty: 1 per person in attic · Blown cellulose and fiberglass generate fine particulates during installation. A standard dust mask is insufficient — use an N95 or higher per manufacturer safety guidance and OSHA guidelines.
- Qty: 1 pair per person · Fiberglass and cellulose particles irritate eyes. Wear sealed goggles (not open-frame glasses) when working in the attic or operating the blower.
- Qty: 1 (optional) · A marked ruler stuck in the insulation lets you confirm you've hit target depth. Most manufacturers include a depth gauge card; you can also cut a wooden stake and mark it at your target depth.
- Qty: 2–4 boards · Never step directly on attic insulation or between joists — you risk stepping through the ceiling. Lay walkboards across the joists to distribute weight safely.
Air sealing (do this FIRST)
- Qty: 2–4 cans for typical attic · Air-seal all penetrations (top plates, plumbing stacks, wiring holes, recessed lights, pull-down stair frames) BEFORE blowing insulation. Air infiltration negates 20–40% of insulation R-value. This is the most cost-effective improvement per DOE guidance.
- Qty: 1 tube per 4–6 recessed lights · Standard spray foam is not rated for contact with recessed light housings (fire hazard). Use listed intumescent caulk around non-IC-rated fixtures, or retrofit IC-rated airtight housings.
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11 items across 4 categories. Quantities assume standard residential practice — adjust up for longer spans, complex geometry, or pro-grade specification.
Blown-In R-Value Formulas
// Forward: depth → R rSettled = depthInitial × (1 − settlingFactor) × rPerInch rInitial = depthInitial × rPerInch // Inverse: target R → required initial depth depthInitial = targetR / (rPerInch × (1 − settlingFactor)) // Bags bagsNeeded = ceil(atticSqft / sqftPerBag) [from coverage chart] // Settling factors (ASTM C739 §11.2) cellulose settlingFactor = 0.175 (17.5% midpoint of 15–20% range) AttiCat settlingFactor = 0.000 (manufacturer specs are settled values)
rPerInch = R-value per inch at settled density (brand-specific). settlingFactor = fraction of thickness lost after 48–72 hr (cellulose: 0.175; AttiCat: 0.000). sqftPerBag = from the manufacturer coverage chart at the nearest R-value tier. ceil() rounds up — you always buy whole bags. Coverage charts already reflect settled R-value per FTC R-Value Rule 16 CFR 460, so depthSettled from the chart equals the labeled R divided by rPerInch.
How This Calculator Estimates
The calculator converts between attic depth (inches) and energy-code R-value using brand-specific coverage data. Exact logic:
1. R-per-inch is brand-specific, not generic. Generic cellulose charts often show "R-3.5/in" as a single number, but actual products vary. Owens Corning AttiCat fiberglass provides R-2.79/in settled (ASTM C687-tested, from the manufacturer's fact sheet PDF). Greenfiber INS515LD provides R-3.33/in; INS541LD provides R-3.22/in (both from the Lowe's product guide, DM-6.3-342 Rev A, 2016). Generic cellulose uses R-3.2/in (FTC R-Value Rule baseline — the FTC does not set a minimum R/inch, only labeling requirements). The calculator uses the brand-specific value for forward and inverse calculations.
2. Settling: what it is and why it matters. Cellulose loose-fill settles 15–20% in thickness within 48–72 hours after installation per ASTM C739 §11.2. A fresh 12-inch pile becomes approximately 9.9–10.2 inches settled. The R-value per inch does NOT change when cellulose settles — only the thickness reduces. This is why the calculator shows both initial depth (what you target during installation) and settled depth (what you'll measure with an attic ruler afterward). AttiCat fiberglass has a settling factor of 0: the AttiCat blowing machine sets the final settled density during installation, so the manufacturer's coverage chart values are already settled values.
3. Coverage charts vs formulas. For AttiCat, Greenfiber INS515LD, and Greenfiber INS541LD, the bag count comes directly from the manufacturer's coverage chart, matched to the nearest R-value tier. These charts are ASTM C687-tested (AttiCat) or FTC R-Value Rule-compliant (Greenfiber). For generic cellulose, there is no brand-specific chart, so the calculator uses an FTC R-Value Rule baseline constant. Always verify the bag count against the coverage chart printed on your specific product's bag at purchase — coverage varies by product revision and bag weight.
4. DOE vs ENERGY STAR targets. The DOE's energystar.gov and energy.gov pages give different recommendations because they have different design bases. DOE energy.gov gives ranges for Zones 1–3 (R-30–49, R-49–60, R-49–60 respectively) — this calculator uses the upper bound as the target "if starting from scratch." ENERGY STAR gives a single value per zone (the lower bound for Zones 1–3: R-30, R-49, R-49). Both are based on the 2021 IECC. Neither is a local code requirement — check your local building authority for the currently adopted code cycle and any amendments.
5. What the calculator doesn't do. This tool sizes a single layer of new blown-in over bare joists. It does not: subtract existing insulation, account for air leakage (seal penetrations first — infiltration negates 20–40% of R-value), compute vapor retarder requirements (IRC R702 / IECC N1102.4 for Zones 5–8 — see DOE energy.gov/energysaver/insulation and verify with your local building department), or check thermal bridging. For top-ups, use our Attic Insulation Calculator; for a quick estimate here, enter (target R − existing R) in Inverse mode.
Common Mistakes — Blown-In Attic Insulation
Three errors that lead homeowners to buy the wrong number of bags or end up with less R-value than expected.
Mistake: Ignoring settling — buying bags for initial depth, not settled R-value
Mistake: Skipping air sealing — insulation without air sealing wastes money
Mistake: Using one bag count for all cellulose brands — 19 lb and 30 lb bags are very different
R-Value vs Depth Quick Reference (by Brand)
From manufacturer coverage charts (AttiCat TDS ASTM C687 2019-Q4; Greenfiber Lowe's guide DM-6.3-342 Rev A 2016-Q4). Bag counts per 1,000 sqft. AttiCat depths are settled values (0% settling — initial ≈ settled). Greenfiber depths are settled values; initial depth is ~17.5% higher. Always verify against current bag label.
| R-value | AttiCat (in) | AttiCat bags/1k sqft | GF-515 (in) | GF-515 bags/1k sqft | GF-541 (in) | GF-541 bags/1k sqft |
|---|---|---|---|---|---|---|
| R-13 | 5.0" | 5.9 | 4.0" | 11.8 | 4.3" | 17.9 |
| R-19 | 7.0" | 9.0 | 5.9" | 18.1 | 6.2" | 27.2 |
| R-30 | 10.75" | 14.6 | 9.2" | 30.8 | 9.6" | 46.1 |
| R-38 | 13.5" | 19.0 | 11.6" | 40.9 | 12.0" | 61.1 |
| R-49 | 17.0" | 25.0 | 14.8" | 56.0 | 15.2" | 83.5 |
| R-60 | 20.5" | 31.5 | 18.0" | 72.4 | 18.4" | 108.1 |
AttiCat: Owens Corning Manufacturers Fact Sheet PDF (ASTM C687; 2019-Q4). GF-515 + GF-541: Greenfiber Lowe's product guide DM-6.3-342 Rev A (2016-Q4). Depths shown are settled depths for all products — AttiCat depths are labeled settled depths (installed depth ≈ labeled depth since fiberglass does not settle appreciably). Verify against current bag label before purchasing. ← Custom dimensions? Use the calculator above
Glossary
R-value
Thermal resistance — how well a material resists heat flow. Higher R means better insulation. R-values are additive: existing R-10 + new R-30 = R-40 total. R-value is NOT a measure of air-sealing; it only measures conductive heat resistance.
R-per-inch
The R-value contributed by one inch of insulation at settled density. Brand-specific: Owens Corning AttiCat fiberglass = 2.79 R/in (ASTM C687); Greenfiber INS515LD cellulose = 3.33 R/in; INS541LD = 3.22 R/in. Generic industry tables often cite 3.5 R/in for cellulose — actual products vary.
Settling
Cellulose loose-fill compresses 15–20% in thickness within 48–72 hours after installation (per Greenfiber product TDS settling guidance, citing ASTM C739 §11.2). Example: 12 inches fresh → ~9.9–10.2 inches settled. The R-value per inch stays the same — only thickness reduces. Owens Corning AttiCat fiberglass has 0% settling: the blowing machine sets final settled density during installation.
Initial depth
The depth of insulation immediately after blowing, before settling. This is the target for your depth-gauge stakes during installation. It is taller than the settled depth by the settling factor (17.5% midpoint for cellulose). The inverse mode of this calculator outputs the required initial depth for your target R.
Settled depth
The depth measured with an attic ruler 48–72 hours after installation. This should match the labeled R-value on the bag divided by the R-per-inch value. Coverage charts per FTC R-Value Rule 16 CFR 460 show settled depths — if you measure right after blowing, the depth will be higher (pre-settling).
Source: FTC 16 CFR 460
Coverage chart
The manufacturer's table showing square feet of coverage per bag at each R-value target. Required on every bag label per FTC R-Value Rule (16 CFR 460); all values reflect settled R-value. AttiCat charts are ASTM C687-tested. Greenfiber charts are from the official product guide (Lowe's DM-6.3-342 Rev A, 2016-Q4).
Source: FTC 16 CFR 460
Climate zone
DOE's 1–8 scale based on heating and cooling degree-days. Zone 1 = hottest (FL, HI, southern TX); Zone 8 = subarctic (AK). Determines the recommended minimum attic R-value from DOE (energy.gov) and ENERGY STAR (energystar.gov). Both are based on the 2021 IECC code cycle.
ASTM C739 (cellulose loose-fill spec)
Standard Specification for Cellulosic Fiber Loose-Fill Thermal Insulation. Governs installed density, settling, moisture resistance, and R-value testing for cellulose insulation. Section §11.2 specifies the 15–20% settling factor used in this calculator. The standard itself is published by ASTM (paid); the practical numbers used in installation are restated on the Greenfiber product TDS, which is free.
ASTM C687 (loose-fill R-value test method)
Practice for Determination of Thermal Resistance of Loose-Fill Building Insulation. Owens Corning AttiCat fiberglass is tested per C687, which measures R-value at installed thickness under specified conditions. AttiCat coverage chart values (e.g., R-30 at 10.75 inches) are ASTM C687-validated settled values. Verify the specific tested R-value and thickness against the current AttiCat product bag label before ordering.
FTC R-Value Rule
Federal Trade Commission rule (16 CFR Part 460) requiring R-value to be tested, labeled, and advertised accurately for all insulation products sold in the US. Requires coverage charts on all bags showing settled values. Does NOT prescribe a minimum R/inch for cellulose — it only governs how R-value is measured and disclosed.
Source: FTC 16 CFR Part 460
Troubleshooting Tips — After Your Install
Covers settling, machine clogs, soffit blocking, recessed lights, and post-install comfort issues — click any item to expand.
I measured 12 inches right after blowing but it's now only 10 inches (verify with your bag-label settling factor) — is that normal?
My blowing machine keeps clogging — what's wrong?
There are bare spots around recessed lights — should I insulate over them?
I bought the wrong number of bags — does the store accept returns on unused bags?
My attic has irregular joists and batts in some areas — how do I calculate depth?
The blown cellulose is covering my soffit vents — is that a problem?
How do I know if I hit the right depth?
I notice a draft in my house even after insulating — did the insulation fail?
Can I add blown cellulose over my existing fiberglass blown-in insulation?
My energy bills haven't improved much after insulating — what else should I check?
Frequently Asked Questions
What R-value does blown-in cellulose have per inch?
Blown-in cellulose has approximately R-3.2 to R-3.8 per inch depending on installed density and product — verify with your bag-label R-per-inch. Greenfiber INS515LD (30 lb bag) provides about R-3.33 per inch settled; INS541LD (19 lb bag) provides about R-3.22 per inch — verify with the Greenfiber bag-label coverage chart. Generic cellulose uses R-3.2 per inch (FTC R-Value Rule baseline). R-per-inch does not change when the insulation settles — only the thickness reduces. Coverage charts from Greenfiber (Lowe's product guide DM-6.3-342 Rev A, 2016-Q4) are the source for these values.
What R-value does blown-in fiberglass (AttiCat) have per inch?
Owens Corning AttiCat blown fiberglass provides approximately R-2.79 per inch at settled density (derived from the ASTM C687-tested specification: R-30 at 10.75 inches installed) — verify with the AttiCat PDS. AttiCat uses an expanding fiber system where the blowing machine sets density automatically — the manufacturer's coverage chart values are settled values, so no additional settling adjustment is needed. Source: AttiCat Product Data Sheet, Owens Corning (2019-Q4, ASTM C687) — verify with the current AttiCat PDS for batch-specific coverage.
How much does blown-in cellulose settle?
Blown-in cellulose loose-fill settles approximately 15–20% in thickness within 48–72 hours after installation per ASTM C739 §11.2 — verify with your bag-label settling specification. For example, 12 inches of freshly blown cellulose settles to about 9.9–10.2 inches (the R-value per inch stays the same — only the thickness reduces) — verify with the manufacturer's coverage chart. Manufacturer coverage charts already account for settling per the FTC R-Value Rule (16 CFR 460): the labeled R-value is the settled R-value. When you use the Inverse mode of this calculator, the initial depth output accounts for settling so you install to the right final depth.
How many bags of blown-in insulation do I need for a 1,500 sqft attic at R-49?
It depends on the brand — verify with each product's bag-label coverage chart. Owens Corning AttiCat (fiberglass) for 1,500 sqft: approximately 38 bags (from coverage chart: 39.9 sqft/bag at R-49) — verify with the AttiCat PDS. Greenfiber INS515LD (30 lb cellulose) for 1,500 sqft: approximately 84 bags (17.9 sqft/bag at R-49) — verify with the Greenfiber coverage chart. Greenfiber INS541LD (19 lb cellulose) for 1,500 sqft: approximately 126 bags (12.0 sqft/bag at R-49) — verify with the Greenfiber INS541LD bag label. Use the calculator above and enter your exact attic area, brand, and target R-value to get the precise count from the manufacturer coverage chart.
What R-value do I need in my attic?
The DOE recommends R-49 to R-60 for most US attics depending on climate zone. Zones 1 (FL, HI): R-30 to R-49. Zones 2–3 (TX, LA, CA, GA): R-49 to R-60. Zones 4–8 (VA through AK): R-60 per DOE. ENERGY STAR recommends R-30 (Zone 1), R-49 (Zones 2–3), and R-60 (Zones 4–8). Use the Climate Zone input in the calculator to see the DOE and ENERGY STAR targets side-by-side for your zone. Source: DOE energy.gov/energysaver/insulation; ENERGY STAR insulation R-values (verified 2026-05-17).
Can I blow cellulose over existing fiberglass batts?
Yes — blown cellulose is compatible over existing fiberglass batts per DOE Energy Saver. The existing fiberglass batts serve as the base layer; the blown cellulose sits on top and fills gaps around batt edges and at the attic perimeter. Before adding any blown insulation, air-seal all penetrations through the ceiling (recessed lights, plumbing stacks, wiring holes) with low-expansion spray foam or intumescent caulk. Air infiltration negates 20–40% of insulation effectiveness regardless of R-value — verify with your local energy auditor for site-specific blower-door results. You do not need to remove the existing batts unless they are wet, moldy, or have a vapor barrier on the wrong side.
Why does the calculator show both an initial and settled depth?
You install insulation at the initial (fresh) depth, but the R-value is measured at the settled depth (after 48–72 hours). The initial depth is what you set your depth gauges to when blowing. The settled depth is what you measure later with an attic ruler — this should match the labeled R-value on the bag. For cellulose, settling is 15–20% (ASTM C739 §11.2). For AttiCat fiberglass, there is no additional settling because the expanding-fiber machine sets the final density at installation — verify with the AttiCat installation guide. The calculator shows both so you know what depth to target during installation (initial) versus what you'll measure afterward (settled).
Is blown-in insulation better than batts?
For attic floors, blown-in is generally preferred over batts for three reasons: (1) Coverage — blown insulation fills around joists, wiring, and obstructions without gaps; batts leave voids at joist edges and penetrations. (2) Air infiltration — blown cellulose especially has some air-resistance properties; batts sit loosely and let air move through. (3) Settling — batts can compress over time in high-humidity attics; blown cellulose and fiberglass maintain performance better. The tradeoff: blown-in requires renting a blower machine; batts can be rolled in by hand. For wall cavities, dense-pack blown insulation (cellulose at 3.5+ lb/ft³) outperforms batts for both R-value and air-sealing.
Related Calculators
- AttiCat R-40 Coverage ChartOwens Corning AttiCat bag-count lookup table by attic area (250–3,000 sq ft) for the common R-40 target. Quick reference for the most-searched AttiCat R-value question.Available now →
- Cellulose Insulation Thickness Chart by R-ValueSettled-depth chart: INS515LD ~14.8 in at R-49, INS541LD ~15.2 in, Applegate ~15.0 in. ASTM C739 settling math + FTC R-Value Rule on settled vs initial depth distinction. Direct depth lookup for cellulose installs.Available now →
- Attic Insulation CalculatorBags of blown-in insulation or batts to reach a target R-value. Enter existing insulation depth and choose brand.Available now →
- Cellulose Insulation CalculatorBags of cellulose insulation for walls or attics. Settled and installed depth.Available now →
- Blown-In Insulation CalculatorBags, depth, and R-value for attic blown-in insulation by material type.Available now →
- Concrete Slab CalculatorCubic yards and bag counts for any slab. IRC R506.1 thickness check.Available now →
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