Washington County, OR Insulation Payback
Washington County attic insulation, by the numbers
DOE classifies Washington County as climate zone 4, marine — a mild coastal climate where the furnace and the AC both mostly stay idle. Its recommended attic R-value for bare joists is 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 2.5 years at an estimated $1,400/year saved. Topping up the attic pays for itself fast here.
The breakdown behind the number
Split it out and it's roughly $1,344 a year on the heating side, $56 on cooling. By estimated insulation savings, Washington County lands in the 45th percentile nationally. Zone 4 alone covers 825 counties in this dataset, and Washington County comes in 395th by savings. Oregon averages $1,557/year across the counties tracked here; Washington County comes in 10% lower.
Washington County's actual weather, not a national average
The heating and cooling degree days behind this estimate — 5,027 HDD and 347 CDD (base 65°F, 1991-2020 normals) — come from FOREST GROVE, OR US, the nearest NOAA station with published normals, 2 miles from Washington County's center. That combined heating-and-cooling load ranks Washington County 2005th nationally by total degree days — the 37th percentile. One local detail the R-value alone won't tell you: Washington County sits in moisture regime C (marine), which can affect the vapor-barrier choice.
Already have some insulation?
Already have a few inches up there? Topping R-11 up to R-49 runs about $2,280 for about $204/year saved — roughly 11.2 years to break even. Call this borderline rather than a clear win.
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 Washington County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Where these figures come from
Washington 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.