About Frost Line Depth

Is Frost Line Depth an Official Government Website?

No. Frost Line Depth is an independent website, not a government service, and no public body endorses it. In the United States the frost line depth is a legal number that each state or local jurisdiction writes into its own building code. We collect those numbers and explain them; we do not set them.

If you need the official answer, these are the bodies that hold it:

Where Does the Data Behind a Result Come From?

There is no national frost depth database. The IRC tells each jurisdiction to fill in the frost line depth column of Table R301.2 with the minimum depth of footing below finish grade, so the number lives in thousands of separate state and local documents. Each result on this site is built from the layers below.

When a place has no published number, we do not fill the gap with an estimate shown as code. The page says no official value was found and shows verified values from nearby places, labelled as someone else’s.

What Do the Labels on Each Place Mean?

Every place page carries one label, and the label tells you how much weight the number can bear.

Verified and state-set values together make up the 721 official values in the lookup. See how we verify for the checks behind each label.

Who Publishes Frost Line Depth?

Frost Line Depth is an independent project. It is not owned by a contractor, a concrete or fencing supplier, a building product maker or a code publisher, and no one pays to change what a page says. We commit to four things:

1. Every frost line depth links to the document it came from, with the date we read it.
2. The way we find and check values is published on the methodology page.
3. Code requirements are kept separate from common practice, and each is labelled.
4. Errors are corrected openly, and the page date changes when a value changes.

Why Does This Site Exist?

Because the most common answer online is wrong for many people. Frost depth maps show one number per state, but in most states the number is set by each city or county, and two neighbouring towns can differ. A ZIP code makes it harder still: it is a mail route, not a building jurisdiction, and nearly a quarter of ZIP areas (23%) have at least 5% of their area in a second county.

We built the site to do three things:

• Give the depth your own jurisdiction sets, with its source, instead of a state average.
• Show plainly when no official number is published, rather than guess.
• Explain what the number means for the thing you are building, from deck footings to water lines.

How Is Content Written and Checked?

Every page follows the same process.

1. Source first. A number is only written down after it has been found in an official code or document.
2. Read in the document. The quote that contains the value is read in context and recorded. Our review log holds 310 checks: 181 confirmed values, 27 corrections and 47 rejections.
3. Reject what does not hold. Real rejections include a document from the wrong state, a table left blank, a plumbing rule (“6 inches below the frost line”) mistaken for a frost depth, and a rainfall figure read as a depth.
4. Label the certainty. Each place gets one of the labels above, never a stronger one than the evidence supports.
5. Date everything. Pages show the month they were checked; each value keeps the date its document was read.
6. Write for the project. Guides state the code rule with its section number, then common practice with the name of whoever recommends it. Where no source exists, the page says so instead of giving a figure.
7. Disclose how drafts are made. Pages are drafted with AI assistance from the sources we collect, and every number is checked against those sources. Read the editorial policy.

Which Sources Does Frost Line Depth Rely On?

The full list is on the sources page. We do not take values from websites that publish frost depth tables or maps without citing a code.

How Does Frost Line Depth Make Money?

It does not at the moment. No page carries advertising or affiliate links today. If advertising is added, these rules apply:

• Ads are labelled and kept apart from the answer.
• Nothing paid changes a value, a label or the text of a requirement.
• No product is recommended because it pays us.

What Does Frost Line Depth Not Do?

The site explains code requirements; it does not replace the people who apply them.

We do not give engineering or legal advice, and we do not report live ground conditions; for those see current frost depth.

How Do You Report an Error?

If a value looks wrong or out of date, send us the place and a link to the official document on the contact page. Documents from building departments are reviewed first. A corrected value goes live with a new date.

Data last checked: October 2026.