Marshall County, AL Insulation Payback
Marshall County attic insulation, by the numbers
DOE classifies Marshall County as climate zone 3, mixed-humid — real heating and real cooling seasons both, roughly balanced across the year. 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 $1,099 a year in heating and cooling — a payback around 2.6 years. Topping up the attic pays for itself fast here.
Heating vs. cooling in Marshall County
Split it out and it's roughly $795 a year on the heating side, $304 on cooling. By estimated insulation savings, Marshall County lands in the 25th percentile nationally. Zone 3 alone covers 690 counties in this dataset, and Marshall County comes in 236th by savings. Alabama averages $1,001/year across the counties tracked here; Marshall County comes in 10% higher.
The climate data behind this
The heating and cooling degree days behind this estimate — 2,995 HDD and 1,910 CDD (base 65°F, 1991-2020 normals) — come from GUNTERSVILLE, AL US, the nearest NOAA station with published normals, 1.8 miles from Marshall County's center. By total degree days, Marshall County sits at the 23th percentile nationally. One local detail the R-value alone won't tell you: Marshall County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
If the attic isn't bare
If Marshall County's attic already has 3-4 inches of old insulation (about R-11) rather than bare joists, the recommended target drops to R-38. That smaller top-up costs around $1,620 and saves an estimated $148/year — payback about 10.9 years. Call this borderline rather than a clear win.
Getting it done in Marshall County
Real bids depend on how easy the attic is to reach and whether old insulation needs removing first, so treat $2,820 as a starting estimate for a Marshall County job, not a quote. Expect at least a $600 minimum charge from most contractors.
Where these figures come from
Marshall County's R-49 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-49 is the target here specifically.