Petroleum County, MT Insulation Payback
Attic insulation payback for Petroleum County, MT
DOE classifies Petroleum County as climate zone 6, cold — cold enough that heating, not cooling, is what decides the bill. Its recommended attic R-value for bare joists is R-60. For an attic around 1,000 square feet, closing the gap from R-2 to R-60 costs around $3,480 and saves an estimated $2,221 a year — payback in roughly 1.6 years. Hard to find a home improvement with a faster payback than this.
Where the savings come from
Of that, about $2,155/year comes from reduced heating and $66/year from reduced cooling load through the ceiling. Petroleum County beats 91% of the counties in this 3,162-county dataset on estimated insulation savings. Among the 459 counties DOE places in zone 6, Petroleum County ranks 169th. Against Montana's own average of $2,182/year, Petroleum County runs 2% above that.
Petroleum County's actual weather, not a national average
Petroleum County's climate figures — 8,058 heating and 411 cooling degree days a year — are read from VALENTINE, MT US, 18.7 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks Petroleum County 302nd nationally by total degree days — the 90th percentile. DOE also classifies Petroleum County as moisture regime B (dry) - ask a local contractor whether that changes the vapor-barrier approach for this job.
If the attic isn't bare
If Petroleum 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 $324/year — payback about 7 years. Topping up the attic pays for itself here.
Quotes and materials for this job
Real bids depend on how easy the attic is to reach and whether old insulation needs removing first, so treat $3,480 as a starting estimate for a Petroleum County job, not a quote. Expect at least a $600 minimum charge from most contractors.
More on how this was built
Nothing here is a guess: the methodology guide names the DOE climate map and NOAA station data behind every number on this page. See the DIY vs. contractor guide for whether a job this size is realistic to do yourself.