Ground Snow Load by State: How to Find Your Design Number
Applies to the ground snow load used to size roof rafters, trusses and beams under the IRC or a state residential code. Above 70 psf, or inside a mapped Case Study (CS) area, the code requires an engineer to set the value — no table, including this one, can substitute for that.
Ground snow load is not like a frost line you can look up once and reuse. The International Residential Code sets one clean rule — prescriptive framing (ordinary wood, cold-formed steel, masonry, concrete and SIP construction) is only covered up to 70 pounds per square foot of ground snow load; above that, an engineer has to design the roof (R301.2.3). But the code leaves the actual number blank for whichever state or city adopts it to fill in, sourced from a national contour map that openly admits it does not work everywhere: mountainous "CS" (Case Study) regions are left blank on purpose, because local variation is too extreme to map at that scale.
That gap has been closed two different ways. A handful of states — concentrated in New England and the Great Lakes, where a wrong number can mean a collapsed roof — wrote their own number directly into their adopted code, by county, town or city. Everywhere else, the modern answer is a free, official, address-level lookup tool: California's and New York's current codes point you to the ASCE 7 Hazard Tool by name, and Oregon requires its own state tool. Neither approach is a "50 states, 50 numbers" chart, because that chart does not exist in the code — and a site that invented one would be less accurate than the real thing, not more.
This guide lays out the rule, the free tool to use where no state number exists, and the seven states that do publish one, with the code section and exact figures for each.
IRC rafter span tables are keyed directly to 30, 50 and 70 psf ground snow load bands; the tool switches tables based on your number. Free, no signup.
The Rule: 70 PSF Separates Prescriptive Framing From Engineered Design
Every roof carries a ground snow load, and the IRC's own rafter and beam span tables are built around three load bands — 30, 50 and 70 pounds per square foot. Table R301.2 leaves the "Ground Snow Load" cell blank for the adopting jurisdiction to fill in (footnote o), normally sourced from the national contour map in Figure R301.2(3)/(4) unless a state publishes its own number instead. Cross the 70 psf line and the prescriptive tables stop applying entirely.
| Requirement | What it says | Code section |
|---|---|---|
| Prescriptive limit | Wood-framed, cold-formed-steel, masonry/concrete and SIP construction covered only up to 70 psf ground snow load | 2021 IRC R301.2.3 |
| Above 70 psf | Roof must be designed by accepted engineering practice — no prescriptive tables apply | 2021 IRC R301.2.3 |
| Who fills in the number | The jurisdiction fills in the Ground Snow Load cell of Table R301.2, normally from Figure R301.2(3)/(4) | 2021 IRC Table R301.2, footnote o |
| Roof design load | Roof designed for the roof live load table or the ground snow load, whichever is greater | 2021 IRC R301.6 |
Why There Is No Clean 50-State Table: A Map With Blank Spots
The IRC's national ground snow load map (Figure R301.2(3)/(4)) marks mountainous regions "CS" — Case Study — meaning the map is deliberately left blank there because local variation is too extreme to show at that scale. Elevation-banded values elsewhere are only valid below the elevation printed in parentheses; above it, the same rule applies: get a site-specific determination. A single number per state would paper over exactly the terrain where getting it wrong is most dangerous.
The Modern Fix: Free Official Lookup Tools, Named in the Code Itself
Recent code editions have started pointing to an online geocoded database instead of a printed map. California's 2025 Residential Code and New York's 2025 Residential Code both cite the ASCE 7 Hazard Tool by name as the source for "location-specific ground snow load values." Oregon goes further and requires its own state tool. If your state is not one of the seven listed below, this is the correct way to get an exact number for your address — not a downloaded frost-map image from a random site.
| Tool | Cited by | Coverage |
|---|---|---|
| ASCE Hazard Tool — ascehazardtool.org | California's and New York's current residential codes | All 50 states, free, address-level |
| SEAO Ground Snow Load Lookup — snowload.seao.org/lookup.html | 2023 Oregon Residential Specialty Code R301.2.3.1 (required) | Oregon only |
Seven States Publish Their Own Ground Snow Load Numbers
In the rest of the country, a state or city fills in the generic map value locally. These seven states instead wrote a real number — or a named source — directly into their own adopted code, overriding the national map for everyone inside their borders. Six cluster in New England and the Great Lakes; Kentucky is the outlier, publishing its own county table even though its values are modest.
| State | How it is set | Adopted code |
|---|---|---|
| Connecticut | Every town, 30–40 psf, in a dedicated appendix | 2022 CT State Building Code (2021 IRC), Appendix AY |
| Kentucky | Every county, mostly 15 psf with 20 psf in a few counties | 2018 Kentucky Residential Code, Table R301.2(1) |
| Massachusetts | Every city and town, 25–60 psf | 780 CMR (MA amendments to 2021 IRC), Table R301.2(2) |
| Michigan | By county, with named city/township exceptions inside counties | Michigan Residential Code, Table R301.2(5) / R 408.30515 |
| Minnesota | Two-tier: 60 psf in 29 named northern counties, 50 psf elsewhere | Minn. R. 1303.1700 |
| New Hampshire | By town, from a named 2002 Army Corps engineering report | NH IRC amendments, Table R301.2 footnote o (ERDC/CRREL TR-02-6) |
| Rhode Island | Every municipality, 25–40 psf, in one table | 2021 IRC with RI Amendments, Table R301.2(2) |
Connecticut: 30–40 PSF, Highest in the Northwest Hills
Connecticut's Appendix AY gives every town its own ground snow load alongside wind speed. Most of the state, including the coast and the Hartford and New Haven areas, is 30 psf. A 35 psf band covers much of the northern interior. The highest values — 40 psf — sit in the northwest hills and one Windham County town.
| Ground snow load | Example towns |
|---|---|
| 30 psf | Bridgeport, Danbury, Hartford, New Haven (Ansonia, Berlin, Bloomfield, Bridgeport, Danbury, Derby, Fairfield, Greenwich, Hartford) |
| 35 psf | Avon, Bristol, Canton, Enfield, Farmington, Granby, Harwinton |
| 40 psf | Canaan, Colebrook, Cornwall, Eastford, Goshen, Kent |
Massachusetts: 25–60 PSF, Every City and Town Gets a Line
Massachusetts publishes a ground snow load, minimum flat roof snow load and ultimate wind speed for all 351 cities and towns in Table R301.2(2) of 780 CMR. The range runs from 25 psf on Aquinnah (Martha's Vineyard) to 60 psf in Adams, in the Berkshires.
| Ground snow load | Example towns |
|---|---|
| 25 psf | Aquinnah (Gay Head) |
| 30 psf | Acushnet |
| 35 psf | Abington, Agawam |
| 40 psf | Alford, Amherst |
| 50 psf | Acton, Amesbury, Andover |
| 60 psf | Adams |
Rhode Island: 25–40 PSF, One Table for All 39 Municipalities
Rhode Island bundles ground snow load, flat roof snow load, wind speed and frost depth into a single table for every municipality. New Shoreham (Block Island) is the state's low point at 25 psf; the highest values, 40 psf, sit in the inland northern towns.
| Ground snow load | Example municipalities |
|---|---|
| 25 psf | New Shoreham (Block Island) |
| 30 psf | Barrington, Bristol, Cranston, Newport, Providence-area towns |
| 35 psf | Coventry, Exeter, Hopkinton, Johnston, Pawtucket |
| 40 psf | Burrillville, Cumberland, Foster, Glocester, Lincoln, North Smithfield |
Michigan: By County, With City and Township Exceptions Inside Counties
Michigan's Table R301.2(5) is unusually granular — it sets a load per county, then carves out specific cities and townships that get a different number inside the same county. Allegan County, for example, is 50 psf everywhere except six named cities and townships, which drop to 35 psf. Alger County, in the Upper Peninsula along Lake Superior, tops the state at 70 psf — the exact ceiling where the prescriptive tables stop applying.
| County | Ground snow load | Exceptions |
|---|---|---|
| Alcona | 50 psf | None listed |
| Alger | 70 psf | None listed — the highest value in the state |
| Allegan | 50 psf | 35 psf in the City of Allegan, City of Otsego, City of Plainwell, City of Wayland, Village of Hopkins, Village of Martin, and the townships of Allegan, Dorr and Gun Plain |
Minnesota: 50 or 60 PSF by County
Minnesota keeps it simple: Rule 1303.1700 sets 60 psf in 29 named northern and central counties, and 50 psf everywhere else in the state — no city-level exceptions.
| Ground snow load | Counties |
|---|---|
| 60 psf | Aitkin, Becker, Beltrami, Carlton, Cass, Clearwater, Cook, Crow Wing, Hubbard, Itasca, Kanabec, Kittson, Koochiching, Lake, Lake of the Woods, Mahnomen, Marshall, Mille Lacs, Morrison, Norman, Otter Tail, Pennington, Pine, Polk, Red Lake, Roseau, St. Louis, Todd, Wadena |
| 50 psf | All other counties |
Kentucky: 15 PSF Statewide, 20 PSF in a Handful of Counties
Kentucky's Table R301.2(1) covers all 120 counties. Loads are modest compared to New England, but the state still chose to publish an explicit county table rather than leave it to the national map — most counties are 15 psf, with Boone, Floyd, Leslie and Letcher stepping up to 20 psf.
| Ground snow load | Counties |
|---|---|
| 15 psf | Most Kentucky counties, including Fayette (Lexington) and the Ohio Valley and Bluegrass regions |
| 20 psf | Boone, Floyd, Leslie, Letcher |
New Hampshire: A Named Report, Not a Table in the Code
New Hampshire takes a different path from its New England neighbors. Instead of printing a table, its amendment to Table R301.2 sends you to a named outside document: "Ground Snow Loads for New Hampshire," ERDC/CRREL TR-02-6, a 2002 report from the Army Corps of Engineers Cold Regions Research and Engineering Laboratory. The report itself is not reproduced in the adopted code text, so for a specific town, confirm the figure with your local building official or a design professional who has the report.
Wisconsin: Its Own Zone Map, Not a Text Table
Wisconsin requires roofs to be designed for "the minimum snow loads listed on the zone map" in its own Uniform Dwelling Code — a real, adopted, state-specific requirement. But the zone boundaries are published as a graphic (Figure 321.02), not as text. Reading exact numbers off a map image is exactly the kind of guesswork this guide avoids, so Wisconsin is not included in the table above — check the figure directly, or ask your local building inspector.
Every Other State: The ASCE Tool or Your Building Department
Outside the seven states above, we checked the state-amended residential code where one exists and found the Ground Snow Load column either unmodified from the generic national-map reference, or absent because the state has no state-specific amended edition at all. In both cases, the correct source is the free ASCE Hazard Tool (or Oregon's SEAO tool) for an address-level number, backed up by your local building department, which has the final say.
| Status | States |
|---|---|
| State code confirmed to still point at the generic national map/tool | California, Indiana, New Jersey, New York, North Carolina, Ohio, Oregon, Utah, Virginia, Washington |
| No state-specific amended edition found — set locally | Alabama, Alaska, Arizona, Arkansas, Colorado, Delaware, District of Columbia, Georgia, Hawaii, Idaho, Illinois, Iowa, Kansas, Louisiana, Maine, Maryland, Mississippi, Missouri, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Vermont, West Virginia, Wyoming |
Standards & Citations
| Standard | Code / Section | Requirement |
|---|---|---|
| IRC Snow Load Prescriptive Limit | 2021 IRC R301.2.3 | Prescriptive framing covered only up to 70 psf ground snow load; engineered design required above it. |
| IRC Climatic and Geographic Design Criteria | 2021 IRC Table R301.2, footnote o | The jurisdiction fills in the ground snow load using the national map, unless it publishes its own value. |
| ASCE Hazard Tool | ASCE 7 Ground Snow Load Geodatabase | Free, address-level ground snow load lookup, cited by name in California's and New York's current residential codes. |
| Oregon Ground Snow Load Determination | 2023 Oregon Residential Specialty Code R301.2.3.1 | Site-specific ground snow load required from the official online tool at snowload.seao.org. |
| Connecticut Wind Speeds, Seismic Design Categories and Ground Snow Loads | 2022 CT State Building Code Appendix AY | Ground snow load of 30 to 40 psf, set per town. |
| Massachusetts Snow Loads and Wind Speeds | 780 CMR Table R301.2(2) | Ground snow load of 25 to 60 psf, set per city and town. |
| Michigan Ground Snow Loads by Jurisdiction | Michigan Residential Code Table R301.2(5) / R 408.30515 | Ground snow load set per county, up to 70 psf, with named city/township exceptions inside counties. |
| Minnesota Ground Snow Load | Minn. R. 1303.1700 | 60 psf in 29 named counties, 50 psf elsewhere in the state. |
| Kentucky Design Snow Criteria | 2018 Kentucky Residential Code Table R301.2(1) | 15 psf in most counties, 20 psf in Boone, Floyd, Leslie and Letcher. |
Apply These Requirements
Open a calculator to run this guide’s requirements against your own project.
Rafter Span Calculator
IRC rafter span tables are keyed directly to 30, 50 and 70 psf ground snow load bands; the tool switches tables based on your number.
Beam Span Calculator
Beam sizing under a roof depends on the tributary snow load carried down from the rafters.
Footing Size Calculator
Footing bearing area is sized from the total load on the foundation, which includes roof snow load in snow country.
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Frequently Asked Questions
What is my ground snow load?
It depends on where you live. Seven states publish their own number in adopted code: Connecticut (30–40 psf by town), Kentucky (15–20 psf by county), Massachusetts (25–60 psf by city/town), Michigan (up to 70 psf by county with local exceptions), Minnesota (50 or 60 psf by county), New Hampshire (by town, from a named 2002 engineering report), and Rhode Island (25–40 psf by municipality). Everywhere else, use the free ASCE Hazard Tool (ascehazardtool.org) for an address-level number, or ask your local building department.
Why isn't there a simple map I can just read?
There is a national map (IRC Figure R301.2(3)/(4)), but the code itself marks mountainous regions "CS" — Case Study — meaning it is deliberately left blank there because local elevation changes make the load too variable to show on one map. Reading a number off that map in hill country can be dangerously wrong, which is exactly why California's and New York's current codes now point to an address-level online tool instead.
What happens if my ground snow load is over 70 psf?
The IRC's prescriptive framing tables — the ones that let a builder pick rafter and joist sizes from a chart — stop applying entirely above 70 psf. IRC R301.2.3 requires the roof structure to be designed by a licensed engineer using accepted engineering practice.
Is ground snow load the same as roof snow load?
No. Ground snow load (Pg) is the raw design input from the map, tool or state table. Roof snow load (the number actually used to size rafters) is derived from it using factors for roof slope, exposure and thermal condition — several of the state tables on this page, like Massachusetts' and Rhode Island's, list both the ground value and a separate "minimum flat roof snow load" side by side.
Can I just use the number a neighboring town uses?
Only if your state's table gives you the same number. In the granular states — Michigan, Massachusetts, Connecticut and Rhode Island especially — adjoining towns can carry different values, and Michigan even splits individual counties between a county-wide number and named city or township exceptions. Always look up your specific municipality rather than assuming a neighbor's figure applies.
Where do the numbers on this page come from?
Every figure was read directly from the adopted code text — ICC Digital Codes state editions for Connecticut, Kentucky, Massachusetts, Michigan, New Hampshire and Rhode Island, and Minnesota's and Wisconsin's state administrative code — not from a third-party map or summary. Sources are cited by section for every table on this page.
Related Code Guides
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