Lewis County, ID Insulation Payback
Lewis County attic insulation, by the numbers
DOE classifies Lewis County as climate zone 5, cold — winters that dominate the energy bill, with cooling a minor factor. 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 $2,015 a year in heating and cooling — a payback around 1.7 years. Topping up the attic pays for itself fast here.
Where the savings come from
Split it out and it's roughly $1,991 a year on the heating side, $24 on cooling. By estimated insulation savings, Lewis County lands in the 83th percentile nationally. Zone 5 alone covers 745 counties in this dataset, and Lewis County comes in 36th by savings. Idaho averages $1,995/year across the counties tracked here; Lewis County comes in 1% higher.
Where these numbers come from
NOAA's NEZPERCE, ID US station, 8.6 miles from Lewis County, supplies the 7,448 HDD and 148 CDD this estimate runs on. Combined heating and cooling load puts Lewis County in the 80th percentile of this 3,162-county dataset. One local detail the R-value alone won't tell you: Lewis County sits in moisture regime B (dry), 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 $294/year saved (~7.8-year payback). Worth doing on the numbers alone.
Getting it done in Lewis County
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 Lewis County's estimated $2,015/year on the line.
Where these figures come from
Lewis 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.