Johnson County, IA Insulation Payback
Johnson County attic insulation, by the numbers
Johnson County sits in IECC climate zone 5 (Cold) — cold enough that heating, not cooling, is what decides the bill. For a currently uninsulated attic, DOE and Energy Star recommend building up to 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 $1,803 a year — payback in roughly 1.9 years.
Topping up the attic pays for itself fast here.
Where the savings come from
Split it out and it's roughly $1,635 a year on the heating side, $168 on cooling. By estimated insulation savings, Johnson County lands in the 73rd percentile nationally. Zone 5 alone covers 754 counties in this dataset, and Johnson County comes in 288th by savings. Iowa averages $1,985/year across the counties tracked here; Johnson County comes in 9% lower.
Where these numbers come from
The heating and cooling degree days behind this estimate — 6,114 HDD and 1,045 CDD (base 65°F, 1991-2020 normals) — come from Iowa City Muni AP, IA US, the nearest NOAA station with published normals, 3.6 miles from Johnson County's center. By total degree days, Johnson County sits at the 75th percentile nationally. One local detail the R-value alone won't tell you: Johnson County sits in moisture regime A (humid), 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 $263/year saved (~8.7-year payback). Call this borderline rather than a clear win.
Getting it done in Johnson County
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 Johnson County job, not a quote. You should get more than one quote before signing anything - expect at least a $600 minimum charge from most contractors.
Where these figures come from
Johnson 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.