Climate Zone 4 (NY downstate, NJ, MD): ceiling R-49 / wall R-20 OR R-13+R-5ci / floor R-19 / slab edge R-10 (2 ft)
IECC R-value (DOE climate-zone) — CZ 4 Envelope R-values (NY downstate)Description
IECC 2021/2024 prescriptive envelope R-values for Climate Zone 4 (Long Island, NYC, much of NJ, MD): ceiling R-49 (R-60 in 2024 high-performance path); wall cavity R-20 in 2×6 framing OR R-13 cavity + R-5 continuous insulation (CI); mass walls R-8/13; floor R-19; basement walls R-10/13 (interior); slab-edge R-10 to 2 ft depth in heated slabs; crawlspace walls R-10/13. Window U-factor ≤ 0.30; SHGC ≤ 0.40.
Why this exists
These prescriptive values are the floor for energy compliance. The R-13+R-5ci wall option (with continuous insulation) is the ENERGY STAR / Indoor airPLUS preferred path — eliminates the stud thermal bridge. Architects should call out the assembly strategy (cavity-only vs cavity + CI) at schematic.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
ceiling | min | 49 | R-value | Ceiling R-49 minimum |
wallCavity | min | 20 | R-value cavity | Wall R-20 cavity (2×6) |
floorCavity | min | 19 | R-value | Floor R-19 |
basementInterior | min | 10 | R-value | Basement wall R-10 (interior) |
windowU | max | 0.3 | U-factor | Window U-factor maximum |
windowSHGC | max | 0.4 | SHGC | Window SHGC maximum |
Categories
Source
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Habitable space minimum ceiling height · IRC R305.1
- Wind design · IRC R301.2.1
- Seismic provisions · IRC R301.2.2
- Snow loads · IRC R301.2.3
- Floodplain construction · IRC R301.2.4
Last reviewed 2026-05-15.