IBC Frost Depth Requirements

What Does the IBC Require for Frost Depth?

The IBC requires footings to be at least 12 inches below the undisturbed ground surface and protected from frost. Section 1809.5 says foundations and other permanent supports shall be protected by one or more of three methods:

1. Extending below the frost line of the locality.
2. Constructing to ASCE 32.
3. Erecting on solid rock.

The footing must also be at least 12 inches wide (1809.4).

Is There an IBC Frost Depth Map?

No. The IBC refers to the frost line of the locality and does not print a map or a number. The depth comes from the local jurisdiction, usually through a local amendment or the design criteria the building department publishes. For residential work, see how the IRC handles it in Table R301.2.

Which Buildings Are Exempt From IBC Frost Protection?

A free-standing building does not need frost protection if all three conditions are met:

• It is Risk Category I.
• It is 600 square feet or less if light-frame, or 400 square feet or less if not.
• Its eave height is 10 feet or less.

Do Exit Landings Need Frost Protection Under the IBC?

Yes, at required exits with doors that swing outward. Section 1809.5.1 requires frost protection at the exterior landing of every required exit with an outward-swinging door, but only to the extent needed to keep the door able to open. The concern is a landing that heaves up and jams the door shut. The IRC has no matching rule for houses.

How Does the IBC Frost Rule Differ From the IRC?

Is Frost Depth Measured to the Top or Bottom of the Footing?

To the bottom of the footing. The depth is from the undisturbed ground surface (or finish grade, in the IRC wording) to the bottom of the footing. Check how your local amendment words it.

How Do Local Codes Amend the IBC Frost Rule?

Many jurisdictions write a number into Section 1809.5 when they adopt the IBC. Examples we read in the adopted codes:

Your jurisdiction may set its own figure the same way, so check its adopted amendments.

How Do You Find the Frost Depth for a Commercial Project?

Ask the authority having jurisdiction and your engineer.

1. Request the frost depth from the building department. Some publish it in design criteria or local amendments.
2. Read the geotechnical report, which may give a frost depth recommendation for the site.
3. Use the ZIP code lookup to see what a nearby residential code sets, as a reference only.

When Is ASCE 32 Used Instead?

When you want a shallower foundation with insulation, including for unheated buildings, ASCE 32 provides the design method. See frost-protected shallow foundations.