Where Code Requires an Ice & Water Barrier — the Map, State by State

What the code actually asks for

The model requirement is IRC Section R905.1.2, “Ice barriers.” It applies in areas with a history of ice forming along the eaves and backing water up under the covering, and it calls for either two layers of cemented underlayment or a self-adhering polymer-modified bitumen sheet, running from the lowest roof edge to a point not less than 24 inches inside the exterior wall line of the heated building.

The self-adhering sheet is the modern answer, and it is a standard-anchored product: it conforms to ASTM D1970, the specification for self-adhering polymer-modified bituminous sheet used as steep-roofing underlayment for ice-dam protection. The membrane seals around the fasteners driven through it, which is the whole point — when water pools behind a dam, there is no path into the deck.

Two things follow from how R905.1.2 is written. First, it is conditional: it bites where the jurisdiction says local ice-damming history exists, which is why the model code hands the decision to a line in each jurisdiction’s Table R301.2(1) climate criteria. Second, that line is exactly what jurisdictions amend — so the real answer is almost never “what does the IRC say,” it is “what did this city write in its own table.”

The two states that split down the middle

Kansas. The Kansas City–side suburbs require it and the Wichita/Topeka side does not. Overland Park, Olathe, Lenexa, Leawood and Johnson County all require an ice barrier 24 inches inside the exterior wall line. Two hundred miles west, Wichita, Sedgwick County, Derby, Haysville, Andover, Butler County, Topeka and Shawnee County all record “Ice Barrier — None Required” in their own adopted tables. The Wichita/Sedgwick County code even explains the mechanism in a footnote: the jurisdiction writes “YES” only where there is a history of local damage from ice damming, and “otherwise, the jurisdiction shall fill in this part of the table with ‘NO.’” Same state, same footnote, opposite answers.

Missouri does the same thing, east to west — and this one catches people, because Missouri is often assumed to be uniform. Every Kansas City–side jurisdiction we cover requires it: Kansas City, Independence, Lee’s Summit, Blue Springs, Liberty, Gladstone, Raytown, Grandview, Grain Valley, Belton, North Kansas City, Clay County and Cass County. Every St. Louis–side jurisdiction we cover does not: St. Louis, St. Louis County, St. Charles County, Chesterfield, O’Fallon, St. Peters and Wentzville. St. Louis’s amendment is explicit rather than silent — its Chapter 25.11 amendment to Table R301.2(1) lists “Ice Shield Underlayment Required: Not Required,” which is a decision the city wrote down, not a gap in our research.

The practical read: in both states the Kansas City metro agrees with itself across the state line, while each state disagrees with its own other half.

Colorado: an elevation question, not a state question

Colorado has the most internally divided record of any state we cover, and elevation explains much of it. Douglas County requires an ice barrier for properties above 7,000 feet, and the Pikes Peak Regional Building Department applies the same 7,000-foot threshold — so within one jurisdiction the answer depends on where the house sits.

Elevation does not explain all of it. Denver and Aurora are adjacent, at essentially the same altitude, and they disagree in writing. Denver’s Roofing Guide and Checklist lists “Ice Barrier Underlayment Required: No,” and states that self-adhering bitumen at the eaves “is NOT required.” Aurora’s Engineering Design Criteria lists “Ice Barrier Underlayment Required: Yes.” Neither is wrong; each filled in its own table. This is the single clearest illustration of why the jurisdiction record, not the state, is the unit that matters.

Oklahoma: required in every valley, statewide

Oklahoma works on a different axis. A statewide amendment carried into local codes adds unconditional triggers on top of whatever a city says about eaves: a 36-inch-wide ice barrier in all valleys, running the length of the valley, and at changes in roof pitch where the lower roof is shallower. Tulsa’s locally amended Section 905.1.2 carries the base eave trigger plus those additions.

So in Oklahoma the honest answer to “is an ice barrier required?” is usually “yes in the valleys, and read the card for the eaves.” Every Oklahoma jurisdiction in this directory that answers the question answers yes.

North Texas: a clean no, in the cities’ own words

Every Dallas–Fort Worth and San Antonio authority we checked writes “No” into its own amended climate table. Fort Worth’s entry cites the ordinance and effective date directly. North Texas has no ice-damming history to design for, and the cities say so on the record rather than leaving the cell blank.

This matters for a roofer bidding across the hail belt: an ice barrier line item that is mandatory in Kansas City is not code-driven in Fort Worth, and an adjuster in either market will know it.

“Not required by code” is not the same as “leave it off”

Three cautions before treating a “No” as permission to omit the membrane.

• The manufacturer can still require it. Shingle installation instructions are enforceable as a condition of the warranty, and several jurisdictions that record “not required” say so explicitly — the requirement returns through the manufacturer’s printed instructions.
• Valleys and penetrations are a separate question from eaves. Oklahoma is the clearest case, but self-adhering membrane at valleys and penetrations is common good practice well outside any mandate.
• It is nearly impossible to add later. The membrane goes on the bare deck during a tear-off. Adding it afterwards means removing the roof, so it is worth settling before the contract is signed rather than after the first ice dam.

For the mechanism — why dams form and why air sealing and insulation matter more than the membrane — see Attic Ventilation and Ice Dams in Colorado. For the full jurisdiction-by-jurisdiction list with each card quoting its own source, see the ice & water shield requirements facet.