Climate Zone 5 (NY upstate, PA, OH, MA): ceiling R-49 / wall R-20 OR R-13+R-5ci / floor R-30 / basement R-15/19 / slab R-10 (4 ft)
IECC R-value (DOE climate-zone) — CZ 5 Envelope R-values (NY upstate)Description
IECC 2021/2024 prescriptive envelope R-values for Climate Zone 5 (much of upstate NY, central PA, OH, MA, IA, IL): ceiling R-49 (R-60 in 2024); wall R-20 cavity or R-13 + R-5ci; floor R-30; basement walls R-15 (continuous) or R-19 (cavity); slab-edge R-10 to 4 ft depth (heated slab); crawlspace R-15/19. Window U-factor ≤ 0.30; SHGC no max in heating-dominated CZ 5.
Why this exists
CZ 5 envelope is meaningfully stronger than CZ 4 — primarily the floor + basement R-values + slab depth. Architects designing in upstate NY versus downstate should consult the IECC tables (or BASC) for the specific zone; defaulting to CZ 4 numbers under-builds.
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 | 30 | R-value | Floor R-30 |
basementInterior | min | 15 | R-value continuous | Basement wall R-15 continuous |
slabEdge | min | 10 | R-value to 4 ft | Heated slab edge R-10 |
windowU | max | 0.3 | U-factor | Window U-factor 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.