Williamson County, TX Insulation Payback
Williamson County attic insulation, by the numbers
DOE classifies Williamson County as climate zone 2, hot-humid — long, muggy summers and mild winters, where cooling dominates the energy bill. Its recommended attic R-value for bare joists is R-49. Topping up a typical 1,000-square-foot attic from bare joists (R-2) to R-49 runs an estimated $2,820, and saves about $955 a year in heating and cooling — a payback around 3 years. Topping up the attic pays for itself fast here.
Heating vs. cooling in Williamson County
Split it out and it's roughly $517 a year on the heating side, $438 on cooling. By estimated insulation savings, Williamson County lands in the 13th percentile nationally. Zone 2 alone covers 233 counties in this dataset, and Williamson County comes in 18th by savings. Texas averages $1,035/year across the counties tracked here; Williamson County comes in 8% lower.
Where these numbers come from
Williamson County's climate figures — 1,949 heating and 2,748 cooling degree days a year — are read from GEORGETOWN LAKE, TX US, 7.1 miles away, NOAA's nearest 1991-2020 normals station. By total degree days, Williamson County sits at the 17th percentile nationally. One local detail the R-value alone won't tell you: Williamson County sits in moisture regime A (humid), which can affect the vapor-barrier choice.
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 $129/year saved — roughly 12.6 years to break even. Call this borderline rather than a clear win.
Getting it done in Williamson County
Get more than one quote before committing. Attic access and any needed air sealing move the price around, and most contractors won't take a job below roughly $600 regardless of size - worth asking upfront given Williamson County's estimated $955/year on the line.
Where these figures come from
Williamson County's R-49 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-49 is the target here specifically.