What Michigan's code says about ice barrier and ice dams

How the Michigan table sets the ice barrier rule

Two layers of text decide whether your roof needs an ice barrier. The first is Michigan’s amended Table R301.2(1), the table where the state fills in local design conditions. It lists “Ice Barrier Underlayment Required” as Yes, with a footnote that ties the answer to a January average temperature of 25 degrees F or less, or a history of ice damming. Michigan did not leave it to each city to decide whether the item applies; the table says yes for the whole state.

The second layer is the code section that says what the barrier is and where it goes. That is R905.1.2 in the 2015 International Residential Code, which Michigan adopts as the Michigan Residential Code for houses. The sections below walk through it. Because the state’s adoption of a newer edition has been held up in court, our guide to the 2015 and 2021 codes explains which edition the quote on your kitchen table should follow.

What R905.1.2 asks for, in numbers

R905.1.2 is short and specific about distance. The rule as the code prints it:

Roof situation	How far the barrier extends	Where it is measured from
Any covered roof surface	At least 24 inches	From the lowest edge of the roof to a point inside the exterior wall line of the building
Slopes of 8:12 or steeper	At least 36 inches, in addition	Along the roof slope, from the eave edge

Two constructions are allowed: either two cemented layers of underlayment or a self-adhering polymer-modified bitumen sheet. The second is what most people mean by “ice and water shield.” There is also an exception for detached accessory structures that have no conditioned floor area.

Most of the confusion starts with the first row. The 24 inches is measured to a point inside the wall line, not from the overhang. A house with a deep overhang therefore needs a wider strip than a house with a short one, because the strip has to cover the overhang first and then run on past the wall. A quote that says “one course at the eave” without saying how far past the wall it reaches does not tell you whether the code is met.

Why the code does not ask for the whole roof

Many roofing pages say the code demands ice and water shield across the entire roof, but the text asks for an eave strip, plus the 36-inch slope measurement on steep roofs. Valleys, around penetrations and other spots can still get extra membrane, but the source for that is the shingle manufacturer’s instructions or your roofer’s judgment, and neither is a code requirement.

A bigger area is not a bad idea, but when a company tells you the code requires the whole roof, you are entitled to ask which section it is quoting. A fair answer is “the code requires the eaves, and we also recommend valleys because…” with a reason you can weigh.

Which roofing materials the rule applies to

R905.1.2 applies where the local table says an ice barrier is required, and it names the coverings it governs: asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles and wood shakes. Metal panels, which are covered by their own section of the code, do not appear on that list, and neither do low-slope membrane roofs. We would not tell a customer with a standing-seam metal roof that a code ice barrier is required, and we would not tell them it is not. Ask the roofer, and ask the building department, because that question belongs to whoever reviews your permit. Our metal roof page covers the other questions that come with that material.

The caveat on Michigan amendments

The wording above is the base ICC 2015 text. The Michigan rules that amend the residential code show none that changes R905.1.2, but that is a medium-confidence statement: the absence of an amendment is not proof that no local ordinance or later rule says something different. If the distances matter for your decision, ask your building department for the number it will inspect against.

Ice dams are an attic story as much as a roof story

An ice barrier is a backup layer that does not stop a dam from forming. ENERGY STAR’s attic air sealing page says that air sealing combined with attic insulation can help to alleviate the formation of dangerous ice dams in the winter, and it lists ice dams as a symptom of an attic that is not sealed, and it treats the attic as the thing to fix.

The code’s ventilation section points the same way. R806.2 sets a minimum net free ventilating area of 1/150 of the vented space, allows 1/300 in some arrangements, and R806.3 asks for a 1-inch air space between insulation and the roof sheathing at eave vents. Those are numbers a roofer can check on a replacement job. Whether they are enough to prevent a dam on your house is a question we cannot answer from a government source, and we will not pretend otherwise.

Nothing on this page leans on the Department of Energy’s or Michigan State University Extension’s ice dam pages, because we could not confirm what they say.

What the state says about insurance and gutters

The Department of Insurance and Financial Services (DIFS) says standard homeowners policies cover a wide range of winter-related disasters, and ice dams are in its list along with burst pipes, wind damage, leaky roofs and a building collapse caused by the weight of ice or snow. Its prevention advice is to keep gutters clean to prevent ice damming, and it adds that coverage depends on the cause and the policy.

Two things follow. First, if water has already come through a ceiling, photograph it before anything is cleaned up and tell your insurer promptly, as DIFS advises. Does homeowners insurance cover a roof leak in Michigan sets out that process in order. Second, clearing gutters is the one prevention step DIFS names, and our gutters page lists what a gutter visit involves.

What a roofer can fix, and what sits outside the roof

A roofer can install the eave barrier to the distances above, lay underlayment that meets the listed standards in R905.1.1, and check the attic vent area against R806.2 while the deck is open. On a tear-off, that is the moment to confirm those items, because the layers below the shingles are visible and changing them later means removing the roof.

A roofer’s scope stops at the roof. Sealing the places where air moves from the house into the attic, and adding insulation, is the project ENERGY STAR describes, and it is done in the attic, often by a different trade. If your ice dams come back after a new roof with a correct barrier, the attic is the next place to look, and a roofing company that tells you the membrane alone will end them has said more than the sources support.

When you compare quotes for a roof that has leaked in winter, ask each company three things in writing: how far past the exterior wall the barrier will run, what the code section behind that number is, and whether the quote includes any attic ventilation work. The roof leak page and the repair or replace tool can help you decide how far the job should go.