AttiCat R-38 Coverage: Bags per 1,000 Sq Ft

Calculate exactly how many Owens Corning AttiCat bags you need at R-38 — using the manufacturer's published coverage figures, top-up delta math, a multi-size attic table, and an honest answer to whether R-38 still meets code.

AttiCat Coverage Chart — R-30 Through R-60

The Owens Corning AttiCat Product Data Sheet (Pub. 10011273-L) publishes coverage at R-13, R-19, R-22, R-26, R-30, R-38, R-44, R-49, and R-60. All rows below come straight from the current 27.5-lb data sheet and match the coverage chart on the AttiCat bag's side panel within rounding. Verify against your bag before purchasing.

R-per-inch for AttiCat fiberglass = 2.79 (derived: R-30 / 10.75 in). Per FTC R-Value Rule 16 CFR Part 460 ↗, coverage charts use a settled-depth basis; AttiCat blown fiberglass does not settle appreciably, so installed depth is final depth.

How the R-38 Bag Count Math Works

AttiCat fiberglass provides a settled R-per-inch of 2.79 (derived from the data sheet: R-30 at 10.75 inches). This is lower than blown cellulose (~3.7 R/in settled) 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.

Why You'll See Two AttiCat R-38 Numbers (27.5 lb vs 28.5 lb)

R-38 is listed directly on the AttiCat coverage chart, so you can plan against it — but if you search for "AttiCat R-38 bags," you will hit two slightly different sets of numbers, and it is not a math error. Owens Corning revised the AttiCat bag from a nominal 28.5 lb (the 2010 Application Instructions) to the current 27.5 lb data sheet, and the R-38 figures changed accordingly:

The practical difference is about half a bag per 1,000 sq ft and half an inch of depth. The takeaway: follow the coverage chart printed on the specific bag you buy, and if you are working from a downloaded PDF, confirm it is the current 27.5-lb revision. A Canadian AttiCat card (a 30.0-lb nominal bag with metric R-steps) circulates too — do not import those numbers for a U.S. R-38 job.

AttiCat R-38 vs Blown Cellulose at R-38

Blown cellulose delivers roughly 3.7 R per inch settled (per the Greenfiber SANCTUARY fact sheet) versus AttiCat at 2.79 R/in, so cellulose reaches R-38 in about 3.5 fewer inches of depth (~10.3 in vs 13.5 in). The trade-off: cellulose needs more bags per 1,000 sq ft but each bag is far cheaper, so material cost is usually lower. AttiCat wins when headroom near the eaves is tight or the attic has a moisture history (fiberglass does not absorb water); cellulose wins when material cost is the priority in a dry attic. For the full cellulose breakdown, use our Cellulose Insulation Calculator — at R-38, Greenfiber SANCTUARY lands near 53 bags per 1,000 sq ft at ~10.3 in settled, roughly half the material cost of AttiCat.

Decision rule: moisture-prone attic or low headroom → AttiCat. Dry attic with adequate clearance and a tight budget → cellulose (about half the material cost at the same R-value).

AttiCat R-38 Bags by Attic Size

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

Depth is constant at 13.5 in; only bag count scales with area. For top-up scenarios, use the delta formula above or the Blown-In R-Value Calculator.

R-38 vs R-30 vs R-49 — Which AttiCat Target Should You Choose?

R-38 is the most common single-target AttiCat job because builder-grade attics often ship at R-19 or R-30, and R-38 is the next meaningful step. Here is how the data-sheet figures compare per 1,000 sq ft (bare attic, 10% buffer included):

Rule of thumb at this range: each extra R-point is roughly 0.4 bag per 1,000 sq ft. The jump from R-38 to R-49 is about 7 more bags per 1,000 sq ft — real money, but it is also the step from "common older target" to "current DOE recommendation." If you are insulating a bare attic in zone 3 or colder, plan for R-49 (or R-60) rather than stopping at R-38. See the R-60 coverage chart for the deep-energy and zone 7-8 case (~32 bags per 1,000 sq ft).

AttiCat R-38 Cost Estimate — DIY and Contractor

Confirm the price at your store before you rely on it — AttiCat pricing changes frequently and varies by region. As a planning estimate as of June 2026, the Owens Corning AttiCat 27.5-lb bag (Home Depot SKU 100541755) lists in the range of roughly $62–$68 per bag (BrickSeek shows a $62 MSRP; recent retail has run near $67–$68). The OC expanding-bagger blower is typically free with 10 or more bags — the 21-bag R-38 order qualifies. Confirm the price and any bulk discount at your local store before purchasing.

Contractor-installed blown fiberglass typically runs in the low single digits per square foot including labor; get local quotes, since labor rates vary widely by market. DIY materials at roughly $1,300–$1,430 per 1,000 sq ft are the savings lever — the blower rental is usually free with the bag purchase.

AttiCat may qualify for the federal Section 25C Energy Efficient Home Improvement Credit (30% of material cost, subject to an annual cap). Verify current status and eligibility at irs.gov — the 25C credit timeline changes frequently. A 30% credit on ~$1,300 in materials would be roughly $390 in potential federal tax savings, if the credit applies in your tax year.

Does R-38 Meet Code? Climate Zone and Code Context

This is the question most R-38 searches are really asking. The honest answer: under the 2021 IECC, R-38 is below the prescriptive attic (ceiling) minimum in every climate zone except zones 1–2. The 2021 IECC ceiling minimums are R-30 (zones 1–2), R-49 (zone 3), and R-60 (zones 4–8), per the DOE Building America Solution Center. Separately, DOE energy.gov and ENERGY STAR recommend R-49 to R-60 for attics in most zones.

Where does that leave R-38? It remains a legitimate target in two cases: (1) zones 1–2, where it exceeds the 2021 IECC ceiling minimum, and (2) warm-zone top-ups, where you are improving an existing R-19 or R-30 attic and R-38 is a budget-friendly bump. Many jurisdictions have not adopted the 2021 IECC, and some older codes still reference R-38 — the 2024 IECC also revised ceiling values again. Because building-code adoption varies by edition and locality, confirm the adopted code and the attic minimum with your local building department before any permitted project. Look up your climate zone by ZIP at energystar.gov.

Rafter Baffles at R-38 Depth

At 13.5 inches of installed blown fiberglass, baffles are required at the eaves. IRC §R806 (verify locally-adopted edition with your local building department) sets the attic free-vent-area requirement at 1:150 (1 sq ft of net free vent area 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 13.5-inch insulation level, before blowing. Without baffles, fiberglass encroaches on the soffit-vent airway and "wind-washes" back from the eaves — especially in standard 2x6 or 2x8 rafter bays.

AttiCat R-38 DIY Install Checklist

Follow these steps in order for a clean R-38 DIY AttiCat install. For top-up scenarios, steps 1–3 determine your actual bag need before purchasing.

1. Find your DOE climate zone — Look up your zone by ZIP at energystar.gov. In zone 3 or colder, plan for R-49 or R-60 rather than stopping at R-38.
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 38 to get your delta R.
3. Calculate bags — Delta R ÷ 2.79 = added inches needed. Use the Blown-In R-Value Calculator or the top-up formula above, then add 10% overage and order.
4. Air-seal first — Seal top plates, electrical penetrations, recessed lights, and duct boots with low-expansion foam or fire-rated caulk. This is near-impossible to do after blowing, and skipping it undercuts effective R-value.
5. Keep clearance from recessed lights and flues — Do not insulate on top of or within 3 inches of non-IC-rated recessed fixtures or similar devices unless they are rated to be covered. This is a fire-safety requirement on the OC instructions.
6. Install rafter baffles — Cardboard or rigid-foam baffles at every eave bay, extending 12+ inches above the planned 13.5-inch depth. Required per IRC §R806 (verify locally-adopted edition with your local building department) .
7. Set depth gauge sticks at 13.5 in — Insert every 4–6 feet across the floor before blowing. AttiCat does not settle — installed depth is final depth.
8. Reserve the AttiCat expanding-bagger blower — NOT the standard cellulose blower. Free with 10+ bags at Home Depot. Confirm availability before buying bags.
9. Install BOTH the bag count AND the depth — Per Owens Corning, hitting depth but skimping on bag count (or vice-versa) yields a lower installed R-value. Blow in 2 passes from eave to ridge to reach the gauge marks.

Common AttiCat R-38 Installation Mistakes

Frequent DIY errors sourced from contractor and inspector guidance — each with a concrete performance or budget cost.

• Buying the bare-attic count when you are topping up — The most common budget error. Ordering 19–21 bags per 1,000 sq ft (bare-attic R-38) when an existing R-19 layer is already there means you over-buy by roughly half. Measure existing depth first and use delta math: R-19 to R-38 is only ~10 bags per 1,000 sq ft; R-30 to R-38 is only ~4.
• Using a standard cellulose blower for AttiCat — AttiCat is compressed fiberglass that must be shredded and expanded by the Owens Corning expanding-bagger. A cellulose blower produces clumped fiberglass with air voids and inconsistent R-value. Confirm you have the correct machine before leaving the store.
• Skipping air sealing and expecting R-38 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 the major bypasses before blowing; otherwise a real portion of your R-38 is bypassed by stack-driven air movement.
• Skipping or short-cutting eaves baffles — At 13.5 inches, the soffit-vent airway is compromised without properly positioned baffles. Blocked soffits raise attic temperatures and let wind push insulation back from the eaves, thinning coverage exactly where it matters.
• Hitting the depth but not the bag count (or vice-versa) — Owens Corning is explicit that you must install both the prescribed number of bags and at least the minimum thickness; doing only one yields a lower installed R-value than the label claims. Set gauge sticks to 13.5 in and track bags used against the chart.
• Trusting the old 28.5-lb numbers — If you plan from the obsolete 2010 chart (51.4 sq ft/bag, 13.0 in), your depth target is half an inch short of the current spec. Use the 27.5-lb chart printed on the bag you actually buy.

Frequently Asked Questions

How many AttiCat bags do I need per 1,000 sq ft at R-38?

Published rate 19 bags per 1,000 sq ft (52.6 sq ft per 27.5-lb bag); buy 21 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-38?

13.5 inches installed on the current 27.5-lb chart (no settling — that is also the final depth). Set gauge sticks to 13.5 inches before blowing. The older 28.5-lb chart listed 13.0 inches.

Does R-38 meet code for my climate zone?

Under the 2021 IECC, the ceiling minimum is R-30 in zones 1–2, R-49 in zone 3, and R-60 in zones 4–8. R-38 exceeds the minimum only in zones 1–2 and is below it in zones 3–8, and it is below current DOE/ENERGY STAR recommendations. R-38 may still satisfy some local codes not on the 2021 IECC — confirm with your local building department.

Why do I see two different AttiCat R-38 numbers?

Two charts circulate: the current 27.5-lb bag (19 bags, 52.6 sq ft/bag, 13.5 in) and an obsolete 2010 28.5-lb chart (19.5 bags, 51.4 sq ft/bag, 13.0 in) still on some retailer PDFs. The difference is about half a bag per 1,000 sq ft. Follow the chart printed on the bag you buy.

How many bags do I need if I am topping up existing insulation to R-38?

Only the added depth counts. From existing R-19 (~6.8 in) to R-38 is ~6.7 added inches — about 10 bags per 1,000 sq ft, not 19. From R-30 (~10.75 in), only ~4 bags. Use the Blown-In R-Value Calculator with your current depth for an estimated result.

Estimates only — verify with your local building authority and a qualified contractor before construction. Brand names are referenced for descriptive purposes (nominative fair use); Owens Corning, AttiCat, and PINK Fiberglas are trademarks of Owens Corning, and CraftedCalcs is not affiliated with or endorsed by these manufacturers. See our full disclaimer.