What R-Value Actually Is
The number matters, but it's not the only thing. Air leakage matters more than people realize. An R-49 attic with a leaky ceiling plane performs like R-20. An R-20 attic with a tight, sealed ceiling plane performs close to its rated value.
Current NY Code for Climate Zone 4
- Attic / ceiling: R-49
- Walls (2x4): R-13 cavity + R-5 continuous
- Walls (2x6): R-20 cavity
- Basement walls: R-15 continuous
- Crawl space walls: R-15 continuous
- Floors over unconditioned space: R-19
For retrofits, NYSERDA typically spec R-60 in attics because the marginal cost of going from R-49 to R-60 is small once the blower is running.
Why You Don't Always Get What the Bag Says
Compression. Batts compressed behind wiring, around junction boxes, or under plumbing lose R-value. A compressed R-19 batt typically performs at R-13-R-15.
Gaps and voids. Insulation that doesn't fill the cavity corner-to-corner loses R-value at the gaps. Loose-fill and dense-pack cellulose fills gaps that batts can't.
Settling. Loose-fill cellulose settles about 10% in the first 6 months. Good installers account for this by blowing to a higher initial depth.
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This guide was written by Carlos Rivera. If your situation has a wrinkle we did not cover, call us direct. Most questions we answer by phone take five minutes.