St. Tammany Parish, LA Insulation Payback
St. Tammany Parish, LA: what topping up your attic actually costs
DOE classifies St. Tammany Parish as climate zone 2, 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. Topping up a typical 1,000-square-foot attic from bare joists (R-2) to R-49 runs an estimated $2,820, and saves about $847 a year in heating and cooling — a payback around 3.3 years. The math clears comfortably within a normal ownership horizon.
Where the savings come from
The estimated savings split roughly $428/year heating, $420/year cooling. Out of every 100 US counties tracked here, St. Tammany Parish's savings potential beats roughly 6 of them. Within zone 2 specifically, it ranks 121st of 233 counties by estimated savings. Louisiana averages $906/year across the counties tracked here; St. Tammany Parish comes in 7% lower.
The climate data behind this
St. Tammany Parish's climate figures — 1,612 heating and 2,634 cooling degree days a year — are read from SLIDELL AP, LA US, 9 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks St. Tammany Parish 2998th nationally by total degree days — the 5th percentile. St. Tammany Parish falls in DOE's moisture regime A (humid), a detail that affects vapor-barrier recommendations more than the R-value target itself.
Already have some insulation?
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 $114/year saved (~14.2-year payback). This one is a genuine toss-up, not a clear yes.
Quotes and materials for this job
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 St. Tammany Parish, not a bid - contractors typically charge a $600 minimum regardless of job size.
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-49 is the target here specifically.