Rhode Island Frost Line Depth by County

Rhode Island publishes a table rather than a single figure: 39 rows running 30 to 40 inches. The full table is below, straight from the code.

It is a count of how much cold a winter delivered: degree days accumulated below 32 degrees over one freezing season. It is the climate quantity the frost provisions of the model building codes are written on, which is why it is the one worth knowing. Foster averages 422 degree days a winter over 50 seasons of the NOAA daily record. It measures the winter, not the ground: the depth for a footing comes from the code.

The state writes its own footing depth for attached accessory structures such as decks, platforms and landings, which is 40 inches below grade, and sets a shallower rule for the stringer supports under exterior stairs. The code also notes: Exterior stairs and steps off decks, balconies and platforms greater than thirty inches (30”) above grade shall have stringer supports extending to twelve inches (12”) below grade. The rule is quoted in full below with a link to it.

Foster averages 134 nights below freezing a year and 32 days that never rise above it, across 50 seasons of the NOAA daily record. The hardest winter in that record was 1976, at 910 degree days. 3 reference cities are measured across Rhode Island and they are all in the table below.

The model residential code most states adopt leaves the frost line depth blank on purpose and marks it as a local determination, because frost depth turns on soil and drainage as much as on air temperature and both change over a few miles. 11 states fill the cell in anyway. The rest name the official who does, which is what the record below carries for Rhode Island.

Rhode Island One and Two Family Dwelling Code (RISBC-2), 510-RICR-00-00-2. It is based on the 2021 International Residential Code. The current edition took effect Dec 1, 2025. Read on September 22, 2026 and linked below.