Frost line depth in Massachusetts

The Massachusetts State Building Code sets frost protection at four feet below finished grade, with narrow exceptions where the foundation bears on sound bedrock or where the bearing material is demonstrably not susceptible to frost heave. Four feet across the whole commonwealth, Cape Cod included.

Massachusetts also does something few states do: it removes the model code’s plumbing chapters entirely and regulates plumbing separately under the state plumbing code administered by the Board of State Examiners of Plumbers and Gas Fitters. We were not able to verify a specific Massachusetts water service burial figure in that separate code, so we state the model-code minimum and say plainly that the commonwealth’s own plumbing rules are the governing document.

One process note worth knowing. The official state code documents are served from a site that blocks automated requests, so our citation for the 48-inch figure is an Internet Archive capture of the state’s own PDF rather than a live link to it. The document is the state’s; the hosting is not.

Across all 69 Massachusetts stations with published normals, the median first 32°F night falls around October 14 and the median station records 52 nights a year below 20°F, which is the coldest threshold NOAA counts and a decent proxy for a hard freeze rather than a light frost. The state’s spread runs from BARRE FALLS DAM, where the median first freeze is October 1, to CHATHAM at November 15.

Massachusetts has the fewest reporting stations of the New England states we cover, 69 in all, and its median first freeze falls on 14 October with about 52 nights a year below 20°F. The coast buys a month: Barre Falls Dam in the central highlands reaches its median first freeze on 1 October, Chatham out on the Cape not until 15 November. A four-foot frost rule is generous for Chatham and reasonable for the Berkshires, which is the trade a single statewide number always makes.

Where these numbers come from

The Massachusetts frost figure was researched against the body that publishes it, and it’s recorded with a confidence note of “state code, archived” in our source ledger. Freeze dates are NOAA normals for stations in the state, picked by a fixed rule rather than by hand: first-order stations, spread west to east. The full method is on our methodology page.

• Freeze dates and cold-night counts: NOAA NCEI U.S. Climate Normals, 1991 to 2020, annual and seasonal by station. Retrieved 2026-09-09. Field definitions are in the by-variable readme.
• ZIP code locations: U.S. Census Bureau 2023 ZIP Code Tabulation Area gazetteer, matched to the nearest station by great-circle distance.
• 780 CMR 51.00 Massachusetts Residential Code, Ch. 3 Building Planning Amendments, Table R301.2(1), Frost line depth: 48 inches (official mass.gov document, fetched via Wayback Machine mirror because mass.gov blocks automated clients) The Massachusetts frost depth figure and basis.
• 780 CMR 51.00, Chapter 29 Plumbing Systems Amendments, confirms plumbing excluded from 780 CMR, governed by 248 CMR (mass.gov document via Wayback Machine mirror) The Massachusetts frost depth figure and basis.
• 780 CMR 1805.4 Frost Protection, foundations to a minimum of four feet below finished grade (mass.gov document, Internet Archive capture; mass.gov blocks automated requests) The Massachusetts frost depth figure and basis.
• 2021 International Residential Code, Section P2603.5 (Freezing), ICC free code viewer The water service line burial rule.

The full method, including how we pick a station and what we do when there is not one close enough, is on our methodology page.