Colleton County, SC Insulation Payback
Attic insulation payback for Colleton County, SC
DOE classifies Colleton County as climate zone 3, hot-humid — long, muggy summers and mild winters, where cooling dominates the energy bill. 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 $937 a year — payback in roughly 3 years. Worth doing on the numbers alone.
Heating vs. cooling in Colleton County
Of that, about $616/year comes from reduced heating and $321/year from reduced cooling load through the ceiling. Colleton County beats 12% of the counties in this 3,162-county dataset on estimated insulation savings. Among the 690 counties DOE places in zone 3, Colleton County ranks 602nd. Against South Carolina's own average of $1,016/year, Colleton County runs 8% below that.
The climate data behind this
Colleton County's climate figures — 2,322 heating and 2,016 cooling degree days a year — are read from WALTERBORO 1 SW, SC US, 2.7 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks Colleton County 2925th nationally by total degree days — the 7th percentile. DOE also classifies Colleton County as moisture regime A (humid) - ask a local contractor whether that changes the vapor-barrier approach for this job.
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). It is close - the payback only just fits a reasonable timeframe.
Getting it done in Colleton County
Real bids depend on how easy the attic is to reach and whether old insulation needs removing first, so treat $2,820 as a starting estimate for a Colleton County job, not a quote. Expect at least a $600 minimum charge from most contractors.
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.