Cook County, IL Insulation Payback
Cook County, IL: what topping up your attic actually costs
DOE classifies Cook County as climate zone 5, cold — a real winter that drives most of the annual energy bill 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 $1,748 a year — payback in roughly 2 years. That's about as fast as attic paybacks get.
The breakdown behind the number
The estimated savings split roughly $1,609/year heating, $138/year cooling. Out of every 100 US counties tracked here, Cook County's savings potential beats roughly 69 of them. Within zone 5 specifically, it ranks 391st of 745 counties by estimated savings. Illinois averages $1,642/year across the counties tracked here; Cook County comes in 6% higher.
Where these numbers come from
Cook County's climate figures — 6,018 heating and 862 cooling degree days a year — are read from CHICAGO NORTHERLY IS, IL US, 3.2 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks Cook County 994th nationally by total degree days — the 69th percentile. Cook County falls in DOE's moisture regime A (humid), a detail that affects vapor-barrier recommendations more than the R-value target itself.
The smaller top-up scenario
If Cook 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 $255/year — payback about 8.9 years. This one is a genuine toss-up, not a clear yes.
Quotes and materials for this job
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 Cook County's estimated $1,748/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.