Marlboro County, SC Insulation Payback
Is attic insulation worth it in Marlboro County, SC?
Marlboro County sits in IECC climate zone 3 (Mixed-Humid) — a genuine mix of cold winters and humid summers, with neither one dominating the bill. For a currently uninsulated attic, DOE and ENERGY STAR recommend building 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 $1,011 a year in heating and cooling — a payback around 2.8 years. Few home upgrades pay back that quickly.
The breakdown behind the number
Heating accounts for about $688/year of that and cooling about $322/year — Marlboro County needs both. Nationally, Marlboro County ranks in the 18th percentile for insulation savings potential. Compared only against its own climate zone, Marlboro County places 446th out of 690. Against South Carolina's own average of $1,016/year, Marlboro County runs 0% above that.
The climate data behind this
The heating and cooling degree days behind this estimate — 2,594 HDD and 2,023 CDD (base 65°F, 1991-2020 normals) — come from MCCOLL 3 NNW, SC US, the nearest NOAA station with published normals, 9.6 miles from Marlboro County's center. Combined heating and cooling load puts Marlboro County in the 14th percentile of this 3,162-county dataset. Its moisture regime is classified humid, which matters for whether the attic needs a vapor retarder as part of the job — worth asking a contractor about locally.
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 $136/year saved (~11.9-year payback). Whether that is worth it depends on how long you plan to stay.
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 Marlboro County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Marlboro County's numbers, sourced
The methodology guide lists exactly which DOE and NOAA sources feed Marlboro County's numbers, and where the cost assumptions come from. See the DIY vs. contractor guide for whether a job this size is realistic to do yourself.