How Much Attic Insulation Do I Need? (R-Value by Zone)

What R-value actually means

R-value measures resistance to heat flow. Higher numbers = better insulation. Doubling R-value cuts heat loss through that surface roughly in half.

An attic with R-19 (about 6" of old fiberglass) loses heat 2.5x faster than an attic at R-49. That's the difference between a comfortable home and chasing drafts every winter.

DOE recommended R-values by climate zone

Zone 1 (Miami, Honolulu): R-30 to R-49

Zone 2 (Houston, Phoenix, Orlando): R-30 to R-60

Zone 3 (Atlanta, Dallas, Los Angeles): R-30 to R-60

Zone 4 (Nashville, Washington DC, Seattle): R-38 to R-60

Zone 5 (Chicago, Boston, Denver): R-49 to R-60

Zone 6 (Minneapolis, Burlington): R-49 to R-60

Zone 7-8 (Duluth, Fairbanks): R-49 to R-60

If your existing insulation is below R-30 anywhere, upgrading is one of the highest-ROI home improvements available.

How many inches that means

Blown cellulose (R-3.7/inch): R-49 = ~13 inches; R-60 = ~16 inches

Blown fiberglass (R-2.5/inch): R-49 = ~20 inches; R-60 = ~24 inches

Closed-cell spray foam (R-6.5/inch): R-49 = ~7.5 inches

Most attics measured today have 4-6 inches of settled insulation — that's R-12 to R-19, well below today's standards.

Air seal first, then add R-value

Adding insulation over unsealed air leaks is throwing money away. A typical home loses 30% of its energy to air leakage at the top plates, recessed lights, plumbing penetrations, and attic hatches.

Have your contractor air-seal the attic floor first (foam around penetrations, weatherstrip the hatch, cover recessed lights with airtight covers), then blow in to the target R-value. The combined upgrade typically pays back in 3-7 years through energy savings.

Typical project cost

Air sealing: $400-$900 for a typical attic

Blown cellulose to R-49: $1.00-$2.75 per sq ft (so $1,500-$4,000 for a 1,500 sq ft attic)

Spray foam at the roof deck (converts attic to conditioned space): $4,000-$10,000+

Most homeowners qualify for the federal 25C credit (30% of materials, up to $1,200/year) plus utility rebates — check our state rebates pages.