Barnwell County, SC Insulation Payback
Barnwell County attic insulation, by the numbers
Barnwell County, South Carolina is zone 3 under DOE's climate map (Hot-Humid), which means humid heat for much of the year, with cooling running far more than heating ever does. An uninsulated attic there should be built up to 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 $952 a year in heating and cooling — a payback around 3 years. Topping up the attic pays for itself fast here.
Heating vs. cooling in Barnwell County
Split it out and it's roughly $632 a year on the heating side, $320 on cooling. By estimated insulation savings, Barnwell County lands in the 13th percentile nationally. Zone 3 alone covers 690 counties in this dataset, and Barnwell County comes in 566th by savings. South Carolina averages $1,016/year across the counties tracked here; Barnwell County comes in 6% lower.
The climate data behind this
Barnwell County's climate figures — 2,383 heating and 2,006 cooling degree days a year — are read from BLACKVILLE 3 W, SC US, 9 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks Barnwell County 2895th nationally by total degree days — the 8th percentile. One local detail the R-value alone won't tell you: Barnwell County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
If the attic isn't bare
A shallower starting point changes the math: with R-11 already down, only the gap to R-38 needs filling, at roughly $1,620 for an estimated $128/year saved (~12.6-year payback). 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 $2,820 figure above as a planning number for Barnwell County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Where these figures come from
Barnwell County's R-49 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-49 is the target here specifically.