Frost-Protected Shallow Foundation: shallow footing with insulation skirt — R-value per air-freezing index

Description

For heated buildings maintained ≥ 64°F monthly mean, footings do not have to extend below the frost line if protected by rigid foam insulation per Figure R403.3(1) and Table R403.3(1). At Air-Freezing Index ≤ 1500 °F-days, no horizontal insulation needed; at AFI 4000 °F-days, R-10.1 vertical + R-13.1 horizontal at corners with insulation extending 36 in. Insulation must be EPS or XPS labeled to ASTM C578. Unheated spaces (porches, garages, carports) and crawl spaces below 64°F cannot use FPSF.

Why this exists

FPSF is the cost-effective alternative to deep-frost footings in cold climates — common in Scandinavia, increasingly used in NY. Architects working in Climate Zones 5-7 should compare an FPSF detail to a 48-in frost footing; FPSF often saves 20-30% on foundation cost. The AFI numbers in Table R403.3(2) tell you which NY counties need which level of insulation.

Categories

Applies to

• Jurisdiction: New York State

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