St. Mary's County, MD Insulation Payback
Is attic insulation worth it in St. Mary's County, MD?
St. Mary's County sits in IECC climate zone 4 (Mixed-Humid) — real heating and real cooling seasons both, roughly balanced across the year. 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 $1,271 a year in heating and cooling — a payback around 2.7 years. Few home upgrades pay back that quickly.
Heating vs. cooling in St. Mary's County
Heating accounts for about $1,034/year of that and cooling about $237/year — St. Mary's County needs both. Nationally, St. Mary's County ranks in the 36th percentile for insulation savings potential. Compared only against its own climate zone, St. Mary's County places 637th out of 825. Against Maryland's own average of $1,395/year, St. Mary's County runs 9% below that.
St. Mary's County's actual weather, not a national average
The heating and cooling degree days behind this estimate — 3,867 HDD and 1,477 CDD (base 65°F, 1991-2020 normals) — come from ST INIGOES WEBSTER NOLF, MD US, the nearest NOAA station with published normals, 8 miles from St. Mary's County's center. By total degree days, St. Mary's County sits at the 36th percentile nationally. 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
Already have a few inches up there? Topping R-11 up to R-49 runs about $2,280 for about $185/year saved — roughly 12.3 years to break even. Whether that is worth it depends on how long you plan to stay.
Getting it done in St. Mary's County
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 St. Mary's County job, not a quote. Expect at least a $600 minimum charge from most contractors.
St. Mary's County's numbers, sourced
The methodology guide lists exactly which DOE and NOAA sources feed St. Mary's 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.