Clarendon County, SC Insulation Payback
Attic insulation payback for Clarendon County, SC
DOE classifies Clarendon County as climate zone 3, mixed-humid — heating load in winter and cooling load in summer, both worth taking seriously here. Its recommended attic R-value for bare joists is 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 $999 a year — payback in roughly 2.8 years. Hard to find a home improvement with a faster payback than this.
The breakdown behind the number
Of that, about $688/year comes from reduced heating and $311/year from reduced cooling load through the ceiling. Clarendon County beats 17% of the counties in this 3,162-county dataset on estimated insulation savings. Among the 690 counties DOE places in zone 3, Clarendon County ranks 473rd. Against South Carolina's own average of $1,016/year, Clarendon County runs 2% below that.
The climate data behind this
The heating and cooling degree days behind this estimate — 2,595 HDD and 1,950 CDD (base 65°F, 1991-2020 normals) — come from MANNING, SC US, the nearest NOAA station with published normals, 2.6 miles from Clarendon County's center. That combined heating-and-cooling load ranks Clarendon County 2761st nationally by total degree days — the 13th percentile. DOE also classifies Clarendon County as moisture regime A (humid) - ask a local contractor whether that changes the vapor-barrier approach for this job.
Already have some insulation?
Already have a few inches up there? Topping R-11 up to R-38 runs about $1,620 for about $135/year saved — roughly 12 years to break even. It is close - the payback only just fits a reasonable timeframe.
Next steps for a Clarendon 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 Clarendon County, not a bid - contractors typically charge a $600 minimum regardless of job size.
More on how this was built
Nothing here is a guess: the methodology guide names the DOE climate map and NOAA station data behind every number on this page. See the DIY vs. contractor guide for whether a job this size is realistic to do yourself.