McNairy County, TN Insulation Payback
McNairy County, TN: what topping up your attic actually costs
McNairy County, Tennessee is zone 3 under DOE's climate map (Mixed-Humid), which means real heating and real cooling seasons both, roughly balanced across the year. An uninsulated attic there should be built up to R-49. For an attic around 1,000 square feet, closing the gap from R-2 to R-49 costs around $2,820 and saves an estimated $1,198 a year — payback in roughly 2.4 years. That's about as fast as attic paybacks get.
The breakdown behind the number
The estimated savings split roughly $914/year heating, $284/year cooling. Out of every 100 US counties tracked here, McNairy County's savings potential beats roughly 31 of them. Within zone 3 specifically, it ranks 99th of 690 counties by estimated savings. Tennessee averages $1,258/year across the counties tracked here; McNairy County comes in 5% lower.
McNairy County's actual weather, not a national average
McNairy County's climate figures — 3,444 heating and 1,782 cooling degree days a year — are read from SELMER, TN US, 2.1 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks McNairy County 2152nd nationally by total degree days — the 32th percentile. McNairy 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?
If McNairy County's attic already has 3-4 inches of old insulation (about R-11) rather than bare joists, the recommended target drops to R-38. That smaller top-up costs around $1,620 and saves an estimated $161/year — payback about 10 years. This one is a genuine toss-up, not a clear yes.
Next steps for a McNairy County attic
Actual quotes will vary by attic access, existing debris, and whether the job needs air sealing first. Treat the $2,820 figure above as a planning number for McNairy 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-49 is the target here specifically.