Grundy County, TN Insulation Payback
Grundy County attic insulation, by the numbers
Grundy County, Tennessee is zone 4 under DOE's climate map (Mixed-Humid), which means heating load in winter and cooling load in summer, both worth taking seriously here. An uninsulated attic there should be built up to 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 $1,328 a year in heating and cooling — a payback around 2.6 years. Topping up the attic pays for itself fast here.
Where the savings come from
Split it out and it's roughly $1,197 a year on the heating side, $131 on cooling. By estimated insulation savings, Grundy County lands in the 41th percentile nationally. Zone 4 alone covers 825 counties in this dataset, and Grundy County comes in 527th by savings. Tennessee averages $1,258/year across the counties tracked here; Grundy County comes in 6% higher.
Where these numbers come from
NOAA's COALMONT, TN US station, 1.8 miles from Grundy County, supplies the 4,477 HDD and 818 CDD this estimate runs on. That combined heating-and-cooling load ranks Grundy County 2087th nationally by total degree days — the 34th percentile. One local detail the R-value alone won't tell you: Grundy County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
If the attic isn't bare
If Grundy 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 $194/year — payback about 11.8 years. Call this borderline rather than a clear win.
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 Grundy County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Where these figures come from
Grundy 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.