Nantucket County, MA Insulation Payback
Nantucket County, MA: what topping up your attic actually costs
DOE classifies Nantucket County as climate zone 5, cold — winters that dominate the energy bill, with cooling a minor factor. Its recommended attic R-value for bare joists is R-60. For an attic around 1,000 square feet, closing the gap from R-2 to R-60 costs around $3,480 and saves an estimated $1,535 a year — payback in roughly 2.3 years.
That's about as fast as attic paybacks get.
The breakdown behind the number
The estimated savings split roughly $1,480/year heating, $55/year cooling. Out of every 100 US counties tracked here, Nantucket County's savings potential beats roughly 55 of them. Within zone 5 specifically, it ranks 716th of 754 counties by estimated savings. Massachusetts averages $1,728/year across the counties tracked here; Nantucket County comes in 11% lower.
The climate data behind this
NOAA's Nantucket MEM AP, MA US station, 3.5 miles from Nantucket County, supplies the 5,536 HDD and 343 CDD this estimate runs on. That combined heating-and-cooling load ranks Nantucket County 1622nd nationally by total degree days — the 49th percentile. Nantucket County falls in DOE's moisture regime A (humid), a detail that affects vapor-barrier recommendations more than the R-value target itself.
Already have some insulation?
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 $224/year saved (~10.2-year payback). This one is a genuine toss-up, not a clear yes.
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 Nantucket County job, not a quote. You should get more than one quote before signing anything - expect at least a $600 minimum charge from most contractors.
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-60 is the target here specifically.