AttiCat R-40 Coverage: Bags per 1,000 Sq Ft

Calculate exactly how many Owens Corning AttiCat bags you need at R-40 — with top-up delta math, a multi-size attic table, and the Zone 4 case for targeting R-40 over the code minimum.

AttiCat Coverage Chart — R-30 Through R-60

The Owens Corning AttiCat TDS (Pub. 10011287-E, ASTM C687 tested) publishes coverage at R-13, R-19, R-22, R-26, R-30, R-38, R-44, R-49, and R-60. R-40 is not a published row — interpolated linearly below from R-38 and R-44; other rows are directly from the TDS and match the AttiCat bag's side-panel coverage chart (labeled "Installed Thickness / R-Value / Bags per 1,000 sq ft") within rounding. Verify against your bag before purchasing.

R-40 interpolated from OC AttiCat TDS (ASTM C687) — not a published row. R-per-inch AttiCat fiberglass = 2.79 (derived: R-30 / 10.75 in). Per FTC R-Value Rule 16 CFR Part 460 ↗, coverage charts use settled-depth basis; AttiCat fiberglass does not settle appreciably.

How the R-40 Bag Count Math Works

AttiCat fiberglass provides a settled R-per-inch of 2.79 (derived from the published TDS: R-30 at 10.75 inches, per ASTM C687 testing). This is lower than blown cellulose (~3.3 R/in) but AttiCat does not settle — the installed depth is the final depth, so no overfill buffer is required. For interactive top-up calculations, the Blown-In R-Value Calculator handles the delta math with any existing depth input.

AttiCat R-40 Bags by Attic Size

Bag counts for common attic sizes (bare attic, 10% buffer included). If your bag's coverage chart lists different sqft/bag values, treat the bag label as authoritative and recalc using those numbers.

Depth is constant; only bag count scales with area. For top-up scenarios, use the delta formula above or the Blown-In R-Value Calculator.

Why Homeowners Target R-40: The Zone 4 Case

R-40 is not a DOE code minimum for any climate zone. The DOE recommends R-38 for Zone 4 top-ups and R-49 for bare Zone 4 attics. Three practical reasons drive homeowners to target R-40 specifically:

• Utility rebate tiers: Some Zone 4 utilities (Mid-Atlantic, Pacific Northwest) offer tiered attic-top-up rebates in the $0.20–$0.40/sq ft range that step up after R-38 — the 2-point premium over R-38 (roughly 1 bag per 1,000 sq ft) can pay for itself. Check your utility's weatherization rebate matrix for exact thresholds.
• Top-up math from a partial job: A homeowner with 5 inches of existing fiberglass (~R-14) who targets R-40 needs only ~9.5 additional inches — about 13 bags per 1,000 sq ft. Jumping to R-49 would require 5 more bags and ~$338 extra per 1,000 sq ft.
• Zone 4-5 border jurisdictions: Some localities on the Zone 4–5 border adopt the stricter Zone 5 code; R-40 becomes an interim target as a practical compromise.

If you are in Zone 5 or colder (Chicago IL, Toledo OH, Denver CO), R-40 falls short of the DOE R-49 recommendation. Add 5 more bags per 1,000 sq ft to reach R-49 — the marginal cost pays back in heating savings within 4–6 years in Zone 5 per DOE estimates.

No Settling Means R-40 Stays R-40

Blown fiberglass does not settle appreciably. Once you install AttiCat to 14.25 inches, that depth is final — no overfill buffer needed. Blown cellulose at R-40 (~12.2 in settled per GreenFiber INS515LD) must be installed at 15–16 inches to account for 15-20% settling. With AttiCat, set depth markers to 14.25 inches and blow to that mark.

AttiCat R-40 vs Blown Cellulose at R-40

Cellulose delivers ~3.3 R per inch vs AttiCat at 2.79 R/in, so it reaches R-40 in about 2 fewer inches of depth (12.2 in vs 14.25 in). The trade-off: cellulose requires ~2.2× more bags per 1,000 sq ft (44 vs 20) and costs roughly half as much in materials (~$660 vs ~$1,352 per 1,000 sq ft). Choose AttiCat when headroom near the eaves is tight or the attic has a moisture history; choose cellulose when material cost is the priority in a dry attic.

AttiCat pricing: HD SKU AC01/100541755 (2026-05-17). GreenFiber INS515LD pricing: Perplexity 2026-05-17. Cellulose R-40 data: GreenFiber INS515LD product guide (DM-6.3-342 Rev A). See our cellulose insulation guide for the full cellulose comparison (~44 bags/1,000 sq ft at R-40).

Decision rule: moisture-prone attic or low headroom → AttiCat. Dry Zone 4 attic with adequate clearance → cellulose (half the material cost at the same R).

R-40 vs R-38 vs R-49 — Which AttiCat Target Should You Choose?

For Zone 4 homeowners topping up over existing insulation: R-38 is the DOE minimum; R-40 exceeds it by 1 bag and ~$68 per 1,000 sq ft; R-49 requires 6 more bags and ~$405 more. For bare Zone 4 attics, DOE recommends R-49 as the starting point. Here is the practical comparison:

Rule of thumb at this range: each extra R-point ≈ 0.3 bag per 1,000 sq ft (~$20/bag-point at HD pricing). The R-38 vs R-40 step is rounding noise; the R-40 vs R-49 step is real money — justify it with Zone 5 climate or a covering utility rebate.

AttiCat R-40 Cost Estimate — DIY and Contractor

As of May 2026, Owens Corning AttiCat 27.5 lb bags retail at approximately $67.58 per bag at Home Depot (SKU 100541755; bulk price $64.20 for 30 or more bags). The expanding-bagger blower is free with 10 or more bags — the 20-bag R-40 order always qualifies. Lowe's pricing was not confirmed this session; verify before purchasing.

• 1,000 sq ft at R-40: ~22 bags (with buffer) x $67.58 = ~$1,487 in materials
• 1,500 sq ft at R-40: ~33 bags x $67.58 = ~$2,230 in materials
• 2,000 sq ft at R-40: ~44 bags x $67.58 = ~$2,974 in materials

Prices: HD product page 2026-05-17; regional variance applies. Confirm bulk rate ($64.20/bag for 30+) at the register.

Contractor-installed blown fiberglass at R-40 typically runs $1.25–$2.00 per sq ft, or $1,250–$2,000 per 1,000 sq ft including labor. DIY materials at ~$1,487 per 1,000 sq ft represent potential savings of $0–$513 vs contractor low estimates, depending on your market.

AttiCat may qualify for the federal Section 25C Energy Efficient Home Improvement Credit (30% of material cost, up to $1,200 annual cap). Verify current status at irs.gov — the 25C credit timeline changes frequently. A 30% credit on $1,487 in materials represents approximately $446 in potential federal tax savings.

Climate Zone and Code Context for R-40

R-40 AttiCat is not a prescriptive DOE or ENERGY STAR minimum target — it sits between two standard tier boundaries. The table below shows where R-40 falls relative to DOE recommendations by zone, sourced from energy.gov and energystar.gov (verified 2026-05-17):

DOE retrofit targets at energy.gov are cost-effectiveness recommendations, not prescriptive code. Look up your zone by ZIP at energystar.gov; your jurisdiction may enforce IECC N1102.1 — confirm the adopted IECC edition and R-value minimum with your local building department before any permitted project. Unpermitted retrofits in Zone 5+: many homeowners pragmatically target R-40 as a budget-friendly improvement, but if you pull a permit expect inspectors to enforce R-49 or higher.

Rafter Baffles Required at R-40 Depth

At 14.25 inches of installed blown fiberglass, baffles are required. IRC §R806 (verify locally-adopted edition with your local building department) sets the attic free-vent-area requirement at 1:150 (1 sq ft per 150 sq ft of attic floor). Install cardboard or rigid-foam baffles at every eave bay, extending at least 12 inches above the planned 14.25-inch insulation level, before blowing. Without baffles, fiberglass encroaches on the soffit-vent airway — particularly in standard 2x6 or 2x8 rafter bays.

AttiCat R-40 DIY Install Checklist

Follow these steps in order for a compliant R-40 DIY AttiCat install. For top-up scenarios, steps 1–2 determine your actual bag need before purchasing.

1. Find your DOE climate zone — Look up your zone by ZIP at energystar.gov. Zone 5 or colder? Target R-49 instead.
2. Measure existing depth — Push a ruler to the subfloor at 3+ locations. Multiply average depth (in) by 2.79 to estimate existing R-value. Subtract from 40 to get your delta R.
3. Calculate bags — Delta R ÷ 2.79 = additional inches needed. Use the Blown-In R-Value Calculator or the top-up formula above. Add 10% overage. Order accordingly.
4. Air-seal first — Seal top plates, electrical penetrations, recessed lights, and duct boots with low-expansion spray foam or fire-rated caulk. Skipping this reduces effective R-value 15-30%.
5. Install rafter baffles — Cardboard or rigid-foam baffles at every eave bay, extending 12+ inches above the planned 14.25-inch depth. Required per IRC §R806 (verify locally-adopted edition with your local building department) .
6. Set depth gauge sticks at 14.25 in — Insert every 4–6 feet across the floor before blowing. AttiCat does not settle — installed depth is final depth.
7. Reserve the AttiCat expanding-bagger blower at HD — NOT the standard cellulose blower. Free with 10+ bags. Confirm availability before purchasing bags.
8. Blow in 2 passes from eave to ridge — First pass for base depth; second pass to hit gauge-stick marks. No overfill needed.

Common AttiCat R-40 Installation Mistakes

Frequent DIY AttiCat install errors sourced from r/Insulation and r/HomeImprovement threads — each with a concrete dollar or performance cost.

• Buying for a bare-attic R-40 when topping up — The most common budget error. Ordering 20 bags per 1,000 sq ft (bare attic target) when an existing R-13 layer already covers the attic means you bought 7 extra bags. Measure existing depth first; use delta math to buy only what you need.
• Using a standard cellulose blower for AttiCat bags — AttiCat uses compressed fiberglass that must be shredded and expanded by the Owens Corning expanding-bagger. A standard cellulose blower produces clumped fiberglass with air voids and inconsistent R-value. Confirm you have the correct machine before leaving the store.
• Skipping rafter baffles at the eaves — At 14.25 inches of blown fiberglass, the soffit-vent airway is compromised without properly positioned baffles. Blocked soffits raise attic summer temperatures 10-20 degrees Fahrenheit, reducing effective R-value performance and accelerating shingle wear on the roof above.
• Skipping air sealing and expecting R-40 to fix drafts — Blown insulation slows conductive heat transfer but does not block convective air movement through open top plates, duct penetrations, and recessed light gaps. Air-seal all major bypasses before blowing; otherwise, a significant portion of your R-40 performance is bypassed by stack-driven air movement.
• Not setting depth marker sticks before blowing — Estimating depth by eye produces thin spots that miss the R-40 target. Set physical gauge sticks marked at 14.25 inches across the attic before starting. Post-install, verify with a ruler at 5+ locations to confirm depth.

Frequently Asked Questions

How many AttiCat bags do I need per 1,000 sq ft at R-40?

Coverage rate ~20 bags/1,000 sq ft; buy 22 bags (rate + 10% buffer). See the R-30 to R-60 table above; confirm against the chart on your specific bag before purchasing.

What is the installed depth of AttiCat at R-40?

14.25 inches installed (no settling — that is also the final depth). Set gauge sticks to 14.25 inches before blowing.

Is R-40 enough for my climate zone?

R-40 exceeds Zone 4's DOE top-up minimum (R-38) but falls below Zone 5's minimum (R-49). In Zone 4 (Washington DC, Louisville KY, Portland OR), R-40 is above code for a top-up. In Zone 5 or colder (Chicago, Denver, Toledo), target R-49 — add 5 more bags per 1,000 sq ft.

How many bags do I need if I am topping up to R-40?

Only the delta depth counts. Existing R-13 (~4.7 in) to R-40 = ~9.5 added inches — about 13–14 bags per 1,000 sq ft, not 20. Use the Blown-In R-Value Calculator with your current depth for an estimated result.

What does AttiCat R-40 cost in materials per 1,000 sq ft?

At $67.58 per bag at Home Depot (May 2026), 22 bags with 10% buffer = approximately $1,487 in materials per 1,000 sq ft. Blower is free with 10+ bags. Bulk rate $64.20/bag for 30+ bags. Verify at your local store.

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