Indiana Frost Line Depth by County

Indiana publishes a table rather than a single figure: 92 rows running 24 to 36 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. Fort Wayne averages 558 degree days a winter over 75 seasons of the NOAA daily record. It measures the winter, not the ground: the depth for a footing comes from the code.

Foundation walls, piers and other permanent supports must be protected from frost, and the first listed way to do that is to extend them below the frost line the county table gives. The code also notes: freestanding accessory structures with an area of 721 square feet or less, when constructed in accordance with Table R309. The rule is quoted in full below with a link to it.

A water service pipe must be at least 12 inches deep and at least 6 inches below the frost line, so in most of the state the county frost depth plus 6 inches is what governs. That comes from the plumbing side of the state code rather than the building side, and the two are not always written to the same number.

Fort Wayne averages 127 nights below freezing a year and 42 days that never rise above it, across 75 seasons of the NOAA daily record. The hardest winter in that record was 1977, at 1,460 degree days. 3 reference cities are measured across Indiana 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 Indiana.

2020 Indiana Residential Code, 675 IAC 14-4.4. It is based on the 2018 International Residential Code, amended by the state. Read on September 23, 2026 and linked below.