Yellowstone County, MT Insulation Payback
Is attic insulation worth it in Yellowstone County, MT?
DOE classifies Yellowstone County as climate zone 6, cold — a real winter that drives most of the annual energy bill here. 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 $2,044 a year in heating and cooling — a payback around 1.7 years. Few home upgrades pay back that quickly.
The breakdown behind the number
Heating accounts for about $1,967/year of that and cooling about $78/year — Yellowstone County needs both. Nationally, Yellowstone County ranks in the 84th percentile for insulation savings potential. Compared only against its own climate zone, Yellowstone County places 358th out of 459. Against Montana's own average of $2,182/year, Yellowstone County runs 6% below that.
Yellowstone County's actual weather, not a national average
NOAA's HUNTLEY EXP STN, MT US station, 1.8 miles from Yellowstone County, supplies the 7,355 HDD and 483 CDD this estimate runs on. Combined heating and cooling load puts Yellowstone County in the 84th percentile of this 3,162-county dataset. Its moisture regime is classified dry, which matters for whether the attic needs a vapor retarder as part of the job — worth asking a contractor about locally.
Already have some insulation?
Already have a few inches up there? Topping R-11 up to R-49 runs about $2,280 for about $298/year saved — roughly 7.6 years to break even. The math clears comfortably within a normal ownership horizon.
Quotes and materials for this job
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 Yellowstone County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Yellowstone County's numbers, sourced
The methodology guide lists exactly which DOE and NOAA sources feed Yellowstone County's numbers, and where the cost assumptions come from. See the DIY vs. contractor guide for whether a job this size is realistic to do yourself.