Lewis County, WA Insulation Payback
Is attic insulation worth it in Lewis County, WA?
Lewis County sits in IECC climate zone 4 (Marine) — a mild coastal climate where the furnace and the AC both mostly stay idle. For a currently uninsulated attic, DOE and ENERGY STAR recommend building 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 $1,398 a year in heating and cooling — a payback around 2.5 years. Few home upgrades pay back that quickly.
The breakdown behind the number
Heating accounts for about $1,360/year of that and cooling about $38/year — Lewis County needs both. Nationally, Lewis County ranks in the 45th percentile for insulation savings potential. Compared only against its own climate zone, Lewis County places 397th out of 825. Against Washington's own average of $1,583/year, Lewis County runs 12% below that.
The climate data behind this
Lewis County's climate figures — 5,086 heating and 237 cooling degree days a year — are read from MAYFIELD PWR PLT, WA US, 11.5 miles away, NOAA's nearest 1991-2020 normals station. That combined heating-and-cooling load ranks Lewis County 2047th nationally by total degree days — the 35th percentile. Its moisture regime is classified marine, which matters for whether the attic needs a vapor retarder as part of the job — worth asking a contractor about locally.
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 $204/year saved (~11.2-year payback). Whether that is worth it depends on how long you plan to stay.
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 Lewis County job, not a quote. Expect at least a $600 minimum charge from most contractors.
Lewis County's numbers, sourced
The methodology guide lists exactly which DOE and NOAA sources feed Lewis 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.