Greenville County, SC Insulation Payback
Greenville County attic insulation, by the numbers
Greenville County, South Carolina is zone 3 under DOE's climate map (Mixed-Humid), which means a genuine mix of cold winters and humid summers, with neither one dominating the bill. 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 $1,026 a year — payback in roughly 2.7 years. Topping up the attic pays for itself fast here.
The breakdown behind the number
Split it out and it's roughly $702 a year on the heating side, $324 on cooling. By estimated insulation savings, Greenville County lands in the 18th percentile nationally. Zone 3 alone covers 690 counties in this dataset, and Greenville County comes in 421st by savings. South Carolina averages $1,016/year across the counties tracked here; Greenville County comes in 1% higher.
Greenville County's actual weather, not a national average
The heating and cooling degree days behind this estimate — 2,646 HDD and 2,035 CDD (base 65°F, 1991-2020 normals) — come from GREENVILLE DWTN AP, SC US, the nearest NOAA station with published normals, 3.5 miles from Greenville County's center. That combined heating-and-cooling load ranks Greenville County 2648th nationally by total degree days — the 16th percentile. One local detail the R-value alone won't tell you: Greenville County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
If the attic isn't bare
If Greenville 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 $138/year — payback about 11.7 years. Call this borderline rather than a clear win.
Next steps for a Greenville 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 Greenville County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Where these figures come from
Greenville 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.