Lewis and Clark County, MT Insulation Payback
Lewis and Clark County attic insulation, by the numbers
Lewis and Clark County, Montana is zone 6 under DOE's climate map (Cold), which means a real winter that drives most of the annual energy bill here. An uninsulated attic there should be built up to R-60. Going from R-2 to the recommended R-60 costs roughly $3,480 installed for a typical attic (about 1,000 sq ft), and pays for itself in about 1.6 years at an estimated $2,146/year saved. Topping up the attic pays for itself fast here.
Where the savings come from
Split it out and it's roughly $2,111 a year on the heating side, $35 on cooling. By estimated insulation savings, Lewis and Clark County lands in the 88th percentile nationally. Zone 6 alone covers 459 counties in this dataset, and Lewis and Clark County comes in 242nd by savings. Montana averages $2,182/year across the counties tracked here; Lewis and Clark County comes in 2% lower.
Lewis and Clark County's actual weather, not a national average
Lewis and Clark County's climate figures — 7,894 heating and 218 cooling degree days a year — are read from ROGERS PASS 9 NNE, MT US, 6.4 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks Lewis and Clark County 406th nationally by total degree days — the 87th percentile. One local detail the R-value alone won't tell you: Lewis and Clark County sits in moisture regime B (dry), which can affect the vapor-barrier choice.
If the attic isn't bare
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 $313/year saved (~7.3-year payback). Worth doing on the numbers alone.
Getting it done in Lewis and Clark County
Actual quotes will vary by attic access, existing debris, and whether the job needs air sealing first. Treat the $3,480 figure above as a planning number for Lewis and Clark County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Where these figures come from
Lewis and Clark 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.