Ada County, ID Insulation Payback
Ada County attic insulation, by the numbers
Ada County, Idaho is zone 5 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. 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 $1,591 a year in heating and cooling — a payback around 2.2 years. Topping up the attic pays for itself fast here.
Where the savings come from
Split it out and it's roughly $1,423 a year on the heating side, $168 on cooling. By estimated insulation savings, Ada County lands in the 59th percentile nationally. Zone 5 alone covers 745 counties in this dataset, and Ada County comes in 649th by savings. Idaho averages $1,995/year across the counties tracked here; Ada County comes in 20% lower.
The climate data behind this
Ada County's climate figures — 5,321 heating and 1,045 cooling degree days a year — are read from BOISE AIR TERMINAL, ID US, 8 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks Ada County 1289th nationally by total degree days — the 59th percentile. One local detail the R-value alone won't tell you: Ada 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 $232/year saved (~9.8-year payback). Call this borderline rather than a clear win.
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 Ada County job, not a quote. Expect at least a $600 minimum charge from most contractors.
Where these figures come from
Ada 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.