Sully County, SD Insulation Payback
Is attic insulation worth it in Sully County, SD?
DOE classifies Sully County as climate zone 6, cold — cold enough that heating, not cooling, is what decides the bill. Its recommended attic R-value for bare joists is R-60. Going from R-2 to the recommended R-60 costs roughly $3,480 installed for a typical attic (about 1,000 sq ft), and pays for itself in about 1.6 years at an estimated $2,174/year saved. Few home upgrades pay back that quickly.
Where the savings come from
Heating accounts for about $2,048/year of that and cooling about $126/year — Sully County needs both. Nationally, Sully County ranks in the 89th percentile for insulation savings potential. Compared only against its own climate zone, Sully County places 213th out of 459. Against South Dakota's own average of $2,162/year, Sully County runs 1% above that.
Sully County's actual weather, not a national average
Sully County's climate figures — 7,660 heating and 782 cooling degree days a year — are read from ONIDA 4 NW, SD US, 0.9 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks Sully County 305th nationally by total degree days — the 90th percentile. 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.
Already have some insulation?
A shallower starting point changes the math: with R-11 already down, only the gap to R-49 needs filling, at roughly $2,280 for an estimated $317/year saved (~7.2-year payback). The math clears comfortably within a normal ownership horizon.
Getting it done in Sully County
Real bids depend on how easy the attic is to reach and whether old insulation needs removing first, so treat $3,480 as a starting estimate for a Sully County job, not a quote. Expect at least a $600 minimum charge from most contractors.
Sully County's numbers, sourced
The methodology guide lists exactly which DOE and NOAA sources feed Sully 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.