St. Johns County, FL Insulation Payback
Is attic insulation worth it in St. Johns County, FL?
St. Johns County, Florida is zone 2 under DOE's climate map (Hot-Humid), which means humid heat for much of the year, with cooling running far more than heating ever does. An uninsulated attic there should be built up to 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 $704 a year in heating and cooling — a payback around 4 years. That is a solid payback as home upgrades go.
The breakdown behind the number
Heating accounts for about $213/year of that and cooling about $491/year — St. Johns County needs both. Nationally, St. Johns County ranks in the 2th percentile for insulation savings potential. Compared only against its own climate zone, St. Johns County places 219th out of 233. Against Florida's own average of $743/year, St. Johns County runs 5% below that.
The climate data behind this
NOAA's ST AUGUSTINE LIGHTHOUSE, FL US station, 6 miles from St. Johns County, supplies the 803 HDD and 3,079 CDD this estimate runs on. Combined heating and cooling load puts St. Johns County in the 2th percentile of this 3,162-county dataset. Its moisture regime is classified humid, which matters for whether the attic needs a vapor retarder as part of the job — worth asking a contractor about locally.
If the attic isn't bare
If St. Johns County's attic already has 3-4 inches of old insulation (about R-11) rather than bare joists, the recommended target drops to R-38. That smaller top-up costs around $1,620 and saves an estimated $95/year — payback about 17.1 years. Whether that is worth it depends on how long you plan to stay.
Getting it done in St. Johns County
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 St. Johns County, not a bid - contractors typically charge a $600 minimum regardless of job size.
St. Johns County's numbers, sourced
The methodology guide lists exactly which DOE and NOAA sources feed St. Johns 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.