St. Mary Parish, LA Insulation Payback
St. Mary Parish, LA: what topping up your attic actually costs
DOE classifies St. Mary 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. 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 $811 a year — payback in roughly 3.5 years. The math clears comfortably within a normal ownership horizon.
Heating vs. cooling in St. Mary Parish
The estimated savings split roughly $327/year heating, $484/year cooling. Out of every 100 US counties tracked here, St. Mary Parish's savings potential beats roughly 4 of them. Within zone 2 specifically, it ranks 162nd of 233 counties by estimated savings. Louisiana averages $906/year across the counties tracked here; St. Mary Parish comes in 10% lower.
Where these numbers come from
NOAA's SALT POINT, LA US station, 5.9 miles from St. Mary Parish, supplies the 1,232 HDD and 3,040 CDD this estimate runs on. By total degree days, St. Mary Parish sits at the 6th percentile nationally. St. Mary 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?
Already have a few inches up there? Topping R-11 up to R-38 runs about $1,620 for about $109/year saved — roughly 14.8 years to break even. This one is a genuine toss-up, not a clear yes.
Getting it done in St. Mary Parish
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. Mary 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.