St. Louis city, MO Insulation Payback
St. Louis city, MO: what topping up your attic actually costs
DOE classifies St. Louis city as climate zone 4, mixed-humid — real heating and real cooling seasons both, roughly balanced across the year. Its recommended attic R-value for bare joists is R-60. For an attic around 1,000 square feet, closing the gap from R-2 to R-60 costs around $3,480 and saves an estimated $1,432 a year — payback in roughly 2.4 years. That's about as fast as attic paybacks get.
Where the savings come from
The estimated savings split roughly $1,148/year heating, $284/year cooling. Out of every 100 US counties tracked here, St. Louis city's savings potential beats roughly 48 of them. Within zone 4 specifically, it ranks 313th of 825 counties by estimated savings. Missouri averages $1,534/year across the counties tracked here; St. Louis city comes in 7% lower.
Where these numbers come from
NOAA's ST LOUIS SCI CTR, MO US station, 1.5 miles from St. Louis city, supplies the 4,292 HDD and 1,769 CDD this estimate runs on. That combined heating-and-cooling load ranks St. Louis city 1486th nationally by total degree days — the 53th percentile. St. Louis city falls in DOE's moisture regime A (humid), a detail that affects vapor-barrier recommendations more than the R-value target itself.
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 $209/year saved (~10.9-year payback). This one is a genuine toss-up, not a clear yes.
Getting it done in St. Louis city
Get more than one quote before committing. Attic access and any needed air sealing move the price around, and most contractors won't take a job below roughly $600 regardless of size - worth asking upfront given St. Louis city's estimated $1,432/year on the line.
Nothing here is a guess
Every figure on this page traces to DOE/IECC climate zones and NOAA degree-day normals, documented in the methodology guide. The guide to what R-value actually means explains why R-60 is the target here specifically.