Attic insulation cost & how much you need
The attic is the highest-payback insulation job in most houses. Two questions decide it: how much material to a target R, and what it costs. Both are short formulas on the prices you enter.
Cost: area, your price, a contingency
total = area × your $/ft² × (1 + contingency). Enter the installed price from your own quote — this site keeps no price list. A 1,200 ft² attic at $1.75/ft² with 10% contingency: 1,200 × 1.75 = 2,100; × 1.10 = $2,310. Run yours in the attic insulation cost tool. Labeled installed bands as a sanity check: blown-in ~$1.00–$2.80/ft², batt ~$0.80–$2.40, closed-cell foam ~$1.50–$4.50.
Quantity: bags to a target R
For loose-fill: depth = target R ÷ R/inch, then bags = ceil(area ÷ coverage-at-R). A 1,200 ft² attic to R-49 in blown fiberglass (~2.5 R/inch, ~28 ft²/bag at R-49): depth = 49 ÷ 2.5 = 19.6 in; bags = ceil(1,200 ÷ 28) = ceil(42.9) = 43 bags. Count it in the attic bag / depth calculator.
Blown-in vs batt in the attic
Same 1,200 ft² attic at R-38, two ways:
| Approach | Coverage | You order |
|---|---|---|
| Blown fiberglass | ~37 ft²/bag | ceil(1200÷37) = 33 bags |
| R-38 batt | ~40 ft²/bundle | ceil(1200÷40) = 30 bundles |
Blown-in flows into irregular joist bays and around obstructions and is fast to install; batts suit open, accessible, regularly-framed attics and give a predictable R with no settling. It's a fit call, not a winner — compare both in the blown-in vs batt attic tool.
Hit the right R for your zone
Attics run R-30 to R-60. Warm zones ~R-30–R-49; cold zones ~R-49–R-60. Look yours up in the attic R-value by climate zone tool before you count bags — the target sets the depth and the depth sets the bag count.
The attic-specific gotchas
- Air-seal before you insulate. Top plates, wire and pipe penetrations, the attic hatch, recessed lights — seal them first, or you're insulating over leaks that no R-value stops.
- Keep the soffit vents clear. Install baffles so loose-fill doesn't choke the eave airflow.
- Don't bury recessed cans unless they're IC-rated — a fire risk otherwise.
- Insulate and weatherstrip the hatch — a bare attic door is a giant hole in your new R-49.
- Blow deep for settling and set rake-depth markers so you actually hit target across the whole attic.
What to measure first
- Attic floor area (add knee walls and dropped soffits).
- Existing R you can add over vs. what needs removal (see the add-over calculator).
- Your target R for the zone.
- The installed $/ft² from an actual quote.
Why the attic pays back first
Heat rises, the attic is usually the biggest single plane in the house, and it's the easiest to reach — so dollar for dollar it returns more than any wall or floor. A typical attic carries 20–35% of a home's conductive loss, and going from a thin R-11–R-19 up to R-49 cuts the loss through that plane by 60–77% (because loss scales with U = 1/R). On a $1,200/yr heating bill with 30% through the attic, that's roughly $215–$275 a year against a job that often runs $1,500–$2,800 — a payback in the high single digits of years on a measure that lasts decades. Run your own numbers in the payback estimator.
Add over, or tear out and start clean?
Most attics you add over: lay unfaced batts or blow loose-fill on top of what's there. added depth = (target R − existing R) ÷ R/inch — existing R-19 to R-49 in cellulose is ~8.6 more inches. You tear out only when the old insulation is wet, moldy, rodent-fouled, or fire/smoke damaged; then budget a removal line (labor plus haul/bags) on top of the new material. Price both halves in the removal & replacement cost tool, and plan the add-over depth in the add-over calculator.
Sanity-checking a contractor's attic quote
Back the quote into a $/ft²: quote total ÷ attic area. A 1,200 ft² attic quoted at $2,600 is ~$2.17/ft² — in-band for blown-in with air-sealing, high for a plain blow, low for closed-cell foam. Then check the two things quotes hide: the target R / installed depth (get it in writing — R-38 vs R-49 is real money) and whether air-sealing, baffles and hatch insulation are included or extra. Do the derived-$/ft² math in the quote check tool — it flags low/in-band/high against the labeled band, which is a sanity guide, not a bid.
Quick numbers to leave with
- Cost = area × your $/ft² × (1 + contingency). 1,200 ft² at $1.75 + 10% = ~$2,310.
- Bags to R-49: ~43 blown-fiberglass bags for 1,200 ft² (~28 ft²/bag), ~19.6" deep.
- Blown vs batt at R-38: ~33 bags vs ~30 bundles for 1,200 ft² — fit call, not a winner.
- Air-seal + baffles + hatch first — they're where a plain blow quietly underperforms.
- Quote check: quote ÷ area = $/ft²; get the target R and air-sealing in writing.
Air-seal, pick the target R, count the bags or bundles, and price it on your own number — the attic usually pays back faster than any other insulation you'll buy.
The figures here follow the conventions published by International Code Council, with practical guidance from NAIMA.