Johnson County, TN Insulation Payback
Johnson County attic insulation, by the numbers
Johnson County sits in IECC climate zone 4 (Mixed-Humid) — real heating and real cooling seasons both, roughly balanced across the year. For a currently uninsulated attic, DOE and ENERGY STAR recommend building 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 $1,395 a year in heating and cooling — a payback around 2.5 years. Topping up the attic pays for itself fast here.
Where the savings come from
Split it out and it's roughly $1,293 a year on the heating side, $102 on cooling. By estimated insulation savings, Johnson County lands in the 45th percentile nationally. Zone 4 alone covers 825 counties in this dataset, and Johnson County comes in 400th by savings. Tennessee averages $1,258/year across the counties tracked here; Johnson County comes in 11% higher.
The climate data behind this
NOAA's MTN CITY 2, TN US station, 3.5 miles from Johnson County, supplies the 4,837 HDD and 632 CDD this estimate runs on. That combined heating-and-cooling load ranks Johnson County 1927th nationally by total degree days — the 39th percentile. One local detail the R-value alone won't tell you: Johnson County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
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 $203/year — payback about 11.2 years. Call this borderline rather than a clear win.
Getting it done in Johnson County
Real bids depend on how easy the attic is to reach and whether old insulation needs removing first, so treat $3,480 as a starting estimate for a Johnson County job, not a quote. Expect at least a $600 minimum charge from most contractors.
Where these figures come from
Johnson 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.