Kentucky Frost Line Depth by County

Kentucky publishes a table rather than a single figure: 20 rows running 24 to 33 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. Lexington averages 190 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.

Exterior footings and foundation walls have to reach the minimum frost protection depth set for the county, measured from finished grade down to the bottom of the footing. The code also notes: Footing and foundation systems may bear on solid rock exposed during preparation of the finished prepared site grade and are then not required to extend below the frost line specified in Table R403.1.4. The rule is quoted in full below with a link to it.

Lexington averages 93 nights below freezing a year and 20 days that never rise above it, across 75 seasons of the NOAA daily record. The hardest winter in that record was 1977, at 722 degree days. 3 reference cities are measured across Kentucky 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 Kentucky.

Kentucky Residential Code (2018 Kentucky Residential Code). It is based on the 2015 International Residential Code for One and Two Family Dwellings. The current edition took effect Dec. 3, 2024. Read on September 23, 2026 and linked below.