LaSalle County, IL Insulation Payback
LaSalle County, IL: what topping up your attic actually costs
DOE classifies LaSalle 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. 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 1.9 years at an estimated $1,800/year saved. That's about as fast as attic paybacks get.
Where the savings come from
The estimated savings split roughly $1,661/year heating, $139/year cooling. Out of every 100 US counties tracked here, LaSalle County's savings potential beats roughly 72 of them. Within zone 5 specifically, it ranks 293rd of 745 counties by estimated savings. Illinois averages $1,642/year across the counties tracked here; LaSalle County comes in 10% higher.
The climate data behind this
The heating and cooling degree days behind this estimate — 6,211 HDD and 865 CDD (base 65°F, 1991-2020 normals) — come from OTTAWA 5SW, IL US, the nearest NOAA station with published normals, 1.6 miles from LaSalle County's center. By total degree days, LaSalle County sits at the 73th percentile nationally. LaSalle County falls in DOE's moisture regime A (humid), a detail that affects vapor-barrier recommendations more than the R-value target itself.
Already have some insulation?
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 $263/year saved (~8.7-year payback). This one is a genuine toss-up, not a clear yes.
Quotes and materials for this job
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 LaSalle County, not a bid - contractors typically charge a $600 minimum regardless of job size.
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.