Colusa County, CA Insulation Payback
Colusa County, CA: what topping up your attic actually costs
DOE classifies Colusa County as climate zone 3, hot-dry — intense summer heat with low humidity, where attic radiant heat gain is the main driver. Its recommended attic R-value for bare joists is R-49. Going from R-2 to the recommended R-49 costs roughly $2,820 installed for a typical attic (about 1,000 sq ft), and pays for itself in about 3.1 years at an estimated $898/year saved. The math clears comfortably within a normal ownership horizon.
Where the savings come from
The estimated savings split roughly $686/year heating, $212/year cooling. Out of every 100 US counties tracked here, Colusa County's savings potential beats roughly 10 of them. Within zone 3 specifically, it ranks 640th of 690 counties by estimated savings. California averages $1,056/year across the counties tracked here; Colusa County comes in 15% lower.
Colusa County's actual weather, not a national average
The heating and cooling degree days behind this estimate — 2,587 HDD and 1,329 CDD (base 65°F, 1991-2020 normals) — come from COLUSA 2 SSW, CA US, the nearest NOAA station with published normals, 11.3 miles from Colusa County's center. Combined heating and cooling load puts Colusa County in the 2th percentile of this 3,162-county dataset. Colusa County falls in DOE's moisture regime B (dry), a detail that affects vapor-barrier recommendations more than the R-value target itself.
The smaller top-up scenario
Already have a few inches up there? Topping R-11 up to R-38 runs about $1,620 for about $121/year saved — roughly 13.4 years to break even. This one is a genuine toss-up, not a clear yes.
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 $2,820 figure above as a planning number for Colusa County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Nothing here is a guess
Every figure on this page traces to DOE/IECC climate zones and NOAA degree-day normals, documented in the methodology guide. The guide to what R-value actually means explains why R-49 is the target here specifically.