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.
For walls, the continuous part of that rating is hard to add from inside a finished house. The easiest time is during a re-side, when rigid foam or insulated vinyl siding can go on over the sheathing.
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.