Granite County, MT Insulation Payback
Granite County, MT: what topping up your attic actually costs
Granite County, Montana is zone 6 under DOE's climate map (Cold), which means cold enough that heating, not cooling, is what decides the bill. 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 1.5 years at an estimated $2,261/year saved. That's about as fast as attic paybacks get.
The breakdown behind the number
The estimated savings split roughly $2,252/year heating, $10/year cooling. Out of every 100 US counties tracked here, Granite County's savings potential beats roughly 92 of them. Within zone 6 specifically, it ranks 127th of 459 counties by estimated savings. Montana averages $2,182/year across the counties tracked here; Granite County comes in 4% higher.
The climate data behind this
Granite County's climate figures — 8,421 heating and 60 cooling degree days a year — are read from PHILLIPSBURG RS, MT US, 8.2 miles away, NOAA's nearest 1991-2020 normals station. Combined heating and cooling load puts Granite County in the 91th percentile of this 3,162-county dataset. Granite County falls in DOE's moisture regime B (dry), a detail that affects vapor-barrier recommendations more than the R-value target itself.
If the attic isn't bare
If Granite County's attic already has 3-4 inches of old insulation (about R-11) rather than bare joists, the recommended target drops to R-49. That smaller top-up costs around $2,280 and saves an estimated $330/year — payback about 6.9 years. That is a solid payback as home upgrades go.
Getting it done in Granite 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 Granite County, 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-60 is the target here specifically.