Union County, SC Insulation Payback
Union County attic insulation, by the numbers
DOE classifies Union 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. 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 2.5 years at an estimated $1,137/year saved. Topping up the attic pays for itself fast here.
The breakdown behind the number
Split it out and it's roughly $874 a year on the heating side, $263 on cooling. By estimated insulation savings, Union County lands in the 27th percentile nationally. Zone 3 alone covers 690 counties in this dataset, and Union County comes in 180th by savings. South Carolina averages $1,016/year across the counties tracked here; Union County comes in 12% higher.
Union County's actual weather, not a national average
Union County's climate figures — 3,296 heating and 1,649 cooling degree days a year — are read from UNION 8 S, SC US, 6.5 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks Union County 2391st nationally by total degree days — the 24th percentile. One local detail the R-value alone won't tell you: Union County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
Already have some insulation?
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 $153/year saved (~10.6-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 Union County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Where these figures come from
Union 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.