Marion County, IL Insulation Payback
Marion County attic insulation, by the numbers
DOE classifies Marion County as climate zone 4, mixed-humid — heating load in winter and cooling load in summer, both worth taking seriously here. Its recommended attic R-value for bare joists is R-60. Going from R-2 to the recommended R-60 costs roughly $3,480 installed for a typical attic (about 1,000 sq ft), and pays for itself in about 2.3 years at an estimated $1,546/year saved. Topping up the attic pays for itself fast here.
Heating vs. cooling in Marion County
Split it out and it's roughly $1,333 a year on the heating side, $213 on cooling. By estimated insulation savings, Marion County lands in the 56th percentile nationally. Zone 4 alone covers 825 counties in this dataset, and Marion County comes in 105th by savings. Illinois averages $1,642/year across the counties tracked here; Marion County comes in 6% lower.
Where these numbers come from
The heating and cooling degree days behind this estimate — 4,985 HDD and 1,328 CDD (base 65°F, 1991-2020 normals) — come from SALEM, IL US, the nearest NOAA station with published normals, 1.5 miles from Marion County's center. Combined heating and cooling load puts Marion County in the 58th percentile of this 3,162-county dataset. One local detail the R-value alone won't tell you: Marion County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
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 $226/year saved (~10.1-year payback). Call this borderline rather than a clear win.
Getting it done in Marion 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 Marion County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Where these figures come from
Marion 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.