St. Clair County, MO Insulation Payback
St. Clair County attic insulation, by the numbers
DOE classifies St. Clair County as climate zone 4, mixed-humid — a genuine mix of cold winters and humid summers, with neither one dominating the bill. Its recommended attic R-value for bare joists is R-60. Topping up a typical 1,000-square-foot attic from bare joists (R-2) to R-60 runs an estimated $3,480, and saves about $1,480 a year in heating and cooling — a payback around 2.4 years. Topping up the attic pays for itself fast here.
Heating vs. cooling in St. Clair County
Split it out and it's roughly $1,241 a year on the heating side, $239 on cooling. By estimated insulation savings, St. Clair County lands in the 52th percentile nationally. Zone 4 alone covers 825 counties in this dataset, and St. Clair County comes in 206th by savings. Missouri averages $1,534/year across the counties tracked here; St. Clair County comes in 4% lower.
Where these numbers come from
St. Clair County's climate figures — 4,640 heating and 1,490 cooling degree days a year — are read from OSCEOLA, MO US, 4 miles away, NOAA's nearest 1991-2020 normals station. Combined heating and cooling load puts St. Clair County in the 55th percentile of this 3,162-county dataset. One local detail the R-value alone won't tell you: St. Clair County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
The smaller top-up scenario
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 $216/year saved (~10.6-year payback). Call this borderline rather than a clear win.
Quotes and materials for this job
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 St. Clair County job, not a quote. Expect at least a $600 minimum charge from most contractors.
Where these figures come from
St. Clair County's R-60 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-60 is the target here specifically.