Berkeley County, SC Insulation Payback
Berkeley County attic insulation, by the numbers
Berkeley 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. Going from R-2 to the recommended R-49 costs roughly $2,820 installed for a typical attic (about 1,000 sq ft), and pays for itself in about 3 years at an estimated $936/year saved.
Topping up the attic pays for itself here.
The breakdown behind the number
Split it out and it's roughly $542 a year on the heating side, $394 on cooling. By estimated insulation savings, Berkeley County lands in the 12th percentile nationally. Zone 3 alone covers 690 counties in this dataset, and Berkeley County comes in 603rd by savings. South Carolina averages $1,016/year across the counties tracked here; Berkeley County comes in 8% lower.
Berkeley County's actual weather, not a national average
The heating and cooling degree days behind this estimate — 2,043 HDD and 2,473 CDD (base 65°F, 1991-2020 normals) — come from Moncks Corner 4 N, SC US, the nearest NOAA station with published normals, 3.1 miles from Berkeley County's center. Combined heating and cooling load puts Berkeley County in the 12th percentile of this 3,171-county dataset. One local detail the R-value alone won't tell you: Berkeley 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 $126/year saved (~12.8-year payback). Call this borderline rather than a clear win.
Next steps for a Berkeley County attic
Actual quotes will vary by attic access, existing debris, and whether the job needs air sealing first, so treat the $2,820 figure above as a planning number for Berkeley County, not a bid. Worth getting quotes from at least two local contractors before committing - most charge a $600 minimum regardless of job size.
Where these figures come from
Berkeley 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.