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Climatic & Geographic Design Parameters by State

Research for the Bones foundation/roof/framing engines. Companion dataset: data/jurisdictions-climate.json (51 entries: 50 states + DC).

Disclaimer: Drafting aid, not engineering. These are state-typical values; the numbers that legally govern a site come from IRC Table R301.2(1), which each local jurisdiction fills in — always verify with the AHJ. Entries AL–MO + DC were reconstructed on 2026-08-13 (the original climate-a research output was lost before merge); each carries a per-entry caveat in the dataset.

The parameters

Field Type What it is
frostLineIn number (inches) Frost penetration depth — how deep the ground freezes. Footings must bear below it or they heave (IRC R403.1.4.1). ~12 in in the Gulf South, 30–42 in mid-Atlantic/midwest, 48–72 in MN/ND/ME/AK.
groundSnowLoadPsf number (psf) ASCE 7 ground snow load pg — the roof's design snow weight. 0 in FL/HI, 50–60+ in New England/upper midwest; mountain "case-study zones" (Sierra, Cascades, Rockies, Wasatch) can exceed 100–300 psf.
ultimateWindMph number (mph) ASCE 7 ultimate design wind speed Vult, Risk Category II. ~105–115 mph inland; 130–180 mph on hurricane coasts (FL/TX/LA/MS/NC/SC + New England islands), with wind-borne-debris opening protection near the coast.
seismicSdc string Seismic Design Category (A–E) for typical site class. A–B: prescriptive framing fine. C: some restrictions. D+: engineered lateral design territory — shear walls, hold-downs, tighter anchorage.
flags object Booleans the engines read directly: hurricaneTies, seismicHoldDowns, hvhz (FL High-Velocity Hurricane Zone), deepFrostFootings (frost ≥ ~36 in).
termiteRisk, weatheringPotential string IRC R301.2 map categories (slight → very heavy; negligible → severe). Informational today — future hooks for treated-sill and concrete-cover rules.
*Note fields string Human-readable range/context per state (frost, snow, wind, seismic) — surfaced as profile notes in the panel UI.

How the engines use them

src/jurisdiction/profiles.ts merges this dataset with jurisdictions-adoption.json into a JurisdictionProfile, and applyJurisdiction() modulates the FramingSpec (LOD 300):

  1. Footing depth = max(12 in, frostLineIn) — the foundation engine digs footings to the frost line, never shallower than the IRC 12 in minimum (R403.1.4 / R403.1.4.1). This is why a Minnesota slab-edge footing renders 42 in deep and an Alabama one 12 in.
  2. Anchor-bolt spacing tightens in SDC D — sill anchorage drops from 6 ft o.c. (IRC R403.1.6 baseline) to 4 ft o.c. when seismicHoldDowns is set (SDC D+ states: CA, AK, HI, NV, OR, UT, WA — state amendments commonly require 4 ft + 3×3 plate washers), and the foundation engine adds hold-downs at shear-wall ends.
  3. Hurricane ties at ultimateWindMph ≥ 130 (or the explicit hurricaneTies flag) — the roof engine adds rafter-to-plate uplift connectors (H2.5-style) in hurricane-prone states (FL, LA, MS, TX, SC, NC, GA, NJ, NY, RI, CT, DE, MA, HI, AL).
  4. Rafter sizing bumps with snow — the default rafter steps 2x6 → 2x8 at pg ≥ 50 psf → 2x10 at ≥ 70 psf, because the R802.4.1 span tables shrink fast under load (a 2x6 that spans ~13 ft at 20 psf drops under 10 ft at 70 psf). The framing-tables dataset then does exact span checks.

Missing states fall back to conservative defaults (frost 12 in, snow 20 psf, wind 115 mph, SDC B) — with all 51 entries present the fallback should never fire; flags also backstop-derive from the numbers (hurricaneTies from wind ≥ 130, seismicHoldDowns from SDC D–F).

Sources