Randolph County, IL Insulation Payback
Randolph County, IL: what topping up your attic actually costs
DOE classifies Randolph County as climate zone 4, mixed-humid — real heating and real cooling seasons both, roughly balanced across the year. Its recommended attic R-value for bare joists is 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 $1,492 a year in heating and cooling — a payback around 2.3 years. That's about as fast as attic paybacks get.
Where the savings come from
The estimated savings split roughly $1,292/year heating, $200/year cooling. Out of every 100 US counties tracked here, Randolph County's savings potential beats roughly 53 of them. Within zone 4 specifically, it ranks 186th of 825 counties by estimated savings. Illinois averages $1,642/year across the counties tracked here; Randolph County comes in 9% lower.
Where these numbers come from
Randolph County's climate figures — 4,833 heating and 1,244 cooling degree days a year — are read from SPARTA 1 W, IL US, 7 miles away, NOAA's nearest 1991-2020 normals station. Combined heating and cooling load puts Randolph County in the 53th percentile of this 3,162-county dataset. Randolph County falls in DOE's moisture regime A (humid), a detail that affects vapor-barrier recommendations more than the R-value target itself.
If the attic isn't bare
A shallower starting point changes the math: with R-11 already down, only the gap to R-49 needs filling, at roughly $2,280 for an estimated $218/year saved (~10.5-year payback). This one is a genuine toss-up, not a clear yes.
Next steps for a Randolph 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 Randolph County's estimated $1,492/year on the line.
Nothing here is a guess
Every figure on this page traces to DOE/IECC climate zones and NOAA degree-day normals, documented in the methodology guide. The guide to what R-value actually means explains why R-60 is the target here specifically.