Johnston County, OK Insulation Payback
Johnston County, OK: what topping up your attic actually costs
DOE classifies Johnston County as climate zone 3, mixed-humid — real heating and real cooling seasons both, roughly balanced across the year. Its recommended attic R-value for bare joists is R-49. Topping up a typical 1,000-square-foot attic from bare joists (R-2) to R-49 runs an estimated $2,820, and saves about $1,153 a year in heating and cooling — a payback around 2.4 years. That's about as fast as attic paybacks get.
Heating vs. cooling in Johnston County
The estimated savings split roughly $829/year heating, $324/year cooling. Out of every 100 US counties tracked here, Johnston County's savings potential beats roughly 28 of them. Within zone 3 specifically, it ranks 159th of 690 counties by estimated savings. Oklahoma averages $1,260/year across the counties tracked here; Johnston County comes in 8% lower.
Where these numbers come from
The heating and cooling degree days behind this estimate — 3,126 HDD and 2,033 CDD (base 65°F, 1991-2020 normals) — come from TISHOMINGO 6N MESONET, OK US, the nearest NOAA station with published normals, 1.9 miles from Johnston County's center. By total degree days, Johnston County sits at the 30th percentile nationally. Johnston 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 Johnston 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 $155/year — payback about 10.4 years. This one is a genuine toss-up, not a clear yes.
Next steps for a Johnston 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 Johnston 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.