Brown County, IL Insulation Payback
Brown County attic insulation, by the numbers
DOE classifies Brown County as climate zone 5, cold — winters that dominate the energy bill, with cooling a minor factor. Its recommended attic R-value for bare joists is R-60. For an attic around 1,000 square feet, closing the gap from R-2 to R-60 costs around $3,480 and saves an estimated $1,633 a year — payback in roughly 2.1 years. Topping up the attic pays for itself fast here.
Where the savings come from
Split it out and it's roughly $1,445 a year on the heating side, $188 on cooling. By estimated insulation savings, Brown County lands in the 62th percentile nationally. Zone 5 alone covers 745 counties in this dataset, and Brown County comes in 601st by savings. Illinois averages $1,642/year across the counties tracked here; Brown County comes in 1% lower.
Brown County's actual weather, not a national average
The heating and cooling degree days behind this estimate — 5,406 HDD and 1,169 CDD (base 65°F, 1991-2020 normals) — come from PERRY 6 NW, IL US, the nearest NOAA station with published normals, 11.5 miles from Brown County's center. That combined heating-and-cooling load ranks Brown County 1166th nationally by total degree days — the 63th percentile. One local detail the R-value alone won't tell you: Brown County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
The smaller top-up scenario
If Brown County's attic already has 3-4 inches of old insulation (about R-11) rather than bare joists, the recommended target drops to R-49. That smaller top-up costs around $2,280 and saves an estimated $238/year — payback about 9.6 years. Call this borderline rather than a clear win.
Getting it done in Brown County
Actual quotes will vary by attic access, existing debris, and whether the job needs air sealing first. Treat the $3,480 figure above as a planning number for Brown County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Where these figures come from
Brown County's R-60 target and its degree-day figures both come from named federal sources - see the methodology guide for exactly which ones. The guide to what R-value actually means explains why R-60 is the target here specifically.