Washington County, IL Insulation Payback
Washington County attic insulation, by the numbers
Washington County, Illinois is zone 4 under DOE's climate map (Mixed-Humid), which means real heating and real cooling seasons both, roughly balanced across the year. An uninsulated attic there should be built up to R-60. Topping up a typical 1,000-square-foot attic from bare joists (R-2) to R-60 runs an estimated $3,480, and saves about $1,509 a year in heating and cooling — a payback around 2.3 years. Topping up the attic pays for itself fast here.
Heating vs. cooling in Washington County
Split it out and it's roughly $1,299 a year on the heating side, $209 on cooling. By estimated insulation savings, Washington County lands in the 54th percentile nationally. Zone 4 alone covers 825 counties in this dataset, and Washington County comes in 156th by savings. Illinois averages $1,642/year across the counties tracked here; Washington County comes in 8% lower.
Where these numbers come from
NOAA's NASHVILLE 1 E, IL US station, 3.2 miles from Washington County, supplies the 4,859 HDD and 1,304 CDD this estimate runs on. By total degree days, Washington County sits at the 55th percentile nationally. One local detail the R-value alone won't tell you: Washington County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
If the attic isn't bare
Already have a few inches up there? Topping R-11 up to R-49 runs about $2,280 for about $220/year saved — roughly 10.4 years to break even. Call this borderline rather than a clear win.
Next steps for a Washington County attic
Get more than one quote before committing. Attic access and any needed air sealing move the price around, and most contractors won't take a job below roughly $600 regardless of size - worth asking upfront given Washington County's estimated $1,509/year on the line.
Where these figures come from
Washington 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.