Johnson County, IL Insulation Payback
Attic insulation payback for Johnson County, IL
DOE classifies Johnson 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. 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 $1,348 a year — payback in roughly 2.6 years. Hard to find a home improvement with a faster payback than this.
Heating vs. cooling in Johnson County
Of that, about $1,125/year comes from reduced heating and $223/year from reduced cooling load through the ceiling. Johnson County beats 42% of the counties in this 3,162-county dataset on estimated insulation savings. Among the 825 counties DOE places in zone 4, Johnson County ranks 488th. Against Illinois's own average of $1,642/year, Johnson County runs 18% below that.
The climate data behind this
NOAA's DIXON SPRINGS AGRIC CTR, IL US station, 11.9 miles from Johnson County, supplies the 4,206 HDD and 1,389 CDD this estimate runs on. That combined heating-and-cooling load ranks Johnson County 1835th nationally by total degree days — the 42th percentile. DOE also classifies Johnson County as moisture regime A (humid) - ask a local contractor whether that changes the vapor-barrier approach for this job.
If the attic isn't bare
If Johnson 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 $197/year — payback about 11.6 years. It is close - the payback only just fits a reasonable timeframe.
Next steps for a Johnson County attic
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 Johnson County, not a bid - contractors typically charge a $600 minimum regardless of job size.
More on how this was built
Nothing here is a guess: the methodology guide names the DOE climate map and NOAA station data behind every number on this page. See the DIY vs. contractor guide for whether a job this size is realistic to do yourself.