"Ice and water shield" is trade shorthand; the code says ice barrier. Code sections below are from the 2021 International Residential Code (IRC). Check the edition and amendments adopted where the house is.
What 2021 IRC R905.1.2 requires, unit: SF / SQ
R905.1.2 requires an ice barrier only where the jurisdiction designates it, then sets the material and how far up the roof it runs. For asphalt shingles, R905.2.7 points back to it.
- Where it applies
- In areas with a history of ice forming along the eaves and causing a backup of water, as designated in Table R301.2. If the jurisdiction hasn't designated it, this section doesn't require an ice barrier.
- Roof coverings
- Asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles and wood shakes.
- What counts
- Not fewer than two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet, used in place of normal underlayment.
- How far
- From the lowest edges of all roof surfaces to a point not less than 24 inches inside the exterior wall line of the building.
- Roofs of 8:12 and steeper
- The ice barrier also has to run not less than 36 inches, measured along the roof slope from the eave edge. The two are separate minimums, so the barrier has to meet both.
- Exception
- Detached accessory structures that don't contain conditioned floor area, such as an unheated detached garage.
How a jurisdiction designates ice-damage areas
The designation sits in the jurisdiction's climatic and geographic design criteria table (Table R301.2 in the 2021 IRC), which each jurisdiction fills in. Its "Ice barrier underlayment required" column is filled in "YES" where there has been a history of local damage from the effects of ice damming, and "NO" otherwise, as the table's footnote directs.
For example, the City of Waterloo, Iowa, publishes its 2021 IRC table with "yes" in that column. A Queen Anne's County, Maryland table posted by the Maryland Department of Labor (amended October 2020) shows "No". Same code section, opposite answers: the model code alone doesn't settle it.
Checklist / Local designation3 items
Where to find the designation
- The adopting ordinance, which usually includes the filled-in table
- The building department's website or roofing handouts
- The permit desk: note the date and who confirmed it
Valleys, low-slope sections and manufacturer instructions, unit: LF / SF
The 2021 IRC doesn't require ice barrier in valleys by name. R905.2.8.2 requires valley linings to be installed per the manufacturer's instructions before shingles go on, and lists the linings it permits:
- Open valley, metal
- At least 24 inches wide, in a corrosion-resistant metal from Table R905.2.8.2.
- Open valley, roll roofing
- Two plies of mineral-surfaced roll roofing, 18 inches (bottom) and at least 36 inches (top) wide.
- Closed valley
- One ply of smooth roll roofing at least 36 inches wide, or either open-valley lining. A self-adhering polymer-modified bitumen underlayment (ASTM D1970) is permitted in place of the lining material.
For low slope, R905.2.2 allows asphalt shingles at 2:12 and steeper, with double underlayment from 2:12 up to 4:12. These facets are easy to miss because they're often a porch or tie-in, not the main roof.
The manufacturer's instructions can go further than the code, and R905.1 ties installation to them where adopted. For example, Owens Corning's current Duration Series installation instructions say:
- Eaves
- Self-adhered ice and water barrier where roofs have had a history of water backup due to ice dams, from the eave edge upslope a minimum of 24 inches from the interior wall line, measured horizontally. Most applications will require 2 courses.
- Closed-cut valleys
- A 36-inch valley liner of self-adhered underlayment or equivalent, or 36-inch, minimum 50 lb smooth-surface roll roofing. Woven and metal valleys are acceptable alternatives.
- Low slope (2:12 to less than 4:12)
- Two layers of synthetic underlayment, or self-adhered ice and water barrier with a 3-inch overlap and metal drip edge.
How to measure ice barrier at the eaves
The overhang sets how far up the slope the ice barrier has to run. The code sets a point inside the wall line; the membrane is laid along the slope to reach it, so the distance up the slope is longer than the level distance.
Checklist / Measuring5 items
Working it out
- Measure the overhang level, from the exterior wall face to the eave edge (note which face)
- Add 24 inches, then multiply by the pitch factor to get the distance up the slope
- On 8:12 and steeper, use 36 inches along the slope if that is more
- Divide by one course's coverage (roll width less the lap in its instructions) and round up
- Multiply the coverage height by the eave length from the measurement report, for every eave
| Overhang (horizontal) | 4:12 (×1.054) | 6:12 (×1.118) | 8:12 (×1.202) | 12:12 (×1.414) |
|---|---|---|---|---|
| None | 25.3 | 26.8 | 28.8, so the 36-inch minimum controls | 33.9, so the 36-inch minimum controls |
| 12 inches | 37.9 | 40.2 | 43.3 | 50.9 |
| 24 inches | 50.6 | 53.7 | 57.7 | 67.9 |
Example (hypothetical numbers): a 6:12 roof with a 24-inch overhang needs about 54 inches up the slope. With a 36-inch roll lapped 3 inches, two courses cover 69 inches (36 + 33). Over 100 LF of eave, that comes to 575 SF before waste. One course would stop well short of the wall line.
Valleys are figured separately: valley length from the measurement report times the liner width you're installing (a 36-inch liner is 3 SF per LF). Low-slope facets come from the report's area and pitch by facet; see the measurement report guide.
Documenting ice barrier on a supplement
A reviewer should be able to rebuild your ice barrier quantity from the file without calling you, so send the designation, the measurements and the calculation, not just the total.
Checklist / Documenting it7 items
What the file needs
- The local designation: the filled-in table, or a dated building department note naming who confirmed it
- The adopted code edition and any local amendment
- A photo of the overhang with a tape at the soffit, readable in the photo
- A pitch gauge photo on each slope with a different pitch
- Eave, valley and low-slope facet figures from the full measurement report
- The product installed, and the instruction page or figure you're citing
- Your calculation in the notes: overhang, pitch factor, courses, square feet
For the rest of the file, use the file checklist and its code and permit notes.
Common gaps between a first scope and the work
Ice barrier gaps can come from a fixed-height quantity or a roof area left out.
- One course everywhere
- Written at a single course when the overhang and the 24-inch rule call for two or more. The soffit photo and the calculation close this gap.
- Steep slopes
- On 8:12 and steeper roofs with a short overhang, the 36-inch slope minimum can control and gets missed.
- Upper eaves
- The section runs from the lowest edges of all roof surfaces, so eaves on upper roofs, dormers and porches can drop off a scope built from the main eave total. Confirm how it's applied locally.
- Valleys
- Written as felt, or left off, when the shingle's instructions call for a self-adhered or roll-roofing liner of a set width.
- Low-slope sections
- A 2:12 to 4:12 porch or tie-in written with single underlayment.
Before ice barrier goes on the estimate
Checklist / Checklist5 items
- The jurisdiction designates it, or the product's instructions call for it
- The overhang is photographed and the slope distance calculated, with the 36-inch minimum checked at 8:12 and steeper
- Every eave is counted, including upper roofs, dormers and porches
- Valley lengths and liner width match the instructions you cite
- The ice barrier area isn't also counted as underlayment
A code section or manufacturer instruction shows what the work requires; whether an item is approved is the carrier's decision, and coverage questions go to the carrier, a licensed public adjuster or an attorney. See also the drip edge guide and the line-item guide. To hand these files to a team that works inside your CRM, see roofing supplements or request an intro call.
Common questions
Is ice and water shield required by code?
Only where the jurisdiction designates it. Under the 2021 IRC (R905.1.2), where adopted, an ice barrier is required in areas marked in Table R301.2 as having a history of ice forming along the eaves. Elsewhere the code section doesn't require it, though the manufacturer's instructions may.
Is ice and water shield required in valleys?
The 2021 IRC doesn't require it in valleys by name. R905.2.8.2 lists permitted valley linings, including a self-adhering ASTM D1970 membrane in place of the lining material, installed per the manufacturer's instructions. Check the instructions for the shingle you install.
What does "24 inches inside the exterior wall line" mean?
The ice barrier has to reach a point at least 24 inches inside the exterior wall line. Measured level, that's the overhang plus 24 inches; converted to distance along the slope, a 6:12 roof with a 12-inch overhang needs about 40 inches.
How many rows of ice and water shield go at the eaves?
As many courses as it takes to reach the required point, which depends on overhang, pitch, roll width and lap. Owens Corning's Duration Series instructions, for example, say most applications will require 2 courses.
How do I show ice and water shield on a supplement?
Send the local designation, a soffit photo with a tape, pitch photos, eave and valley lengths from the measurement report, and your calculation. Cite R905.1.2 as adopted locally and the instructions for the product installed.
Sources
- International Code Council, 2021 International Residential Code: R905.1.2, R905.2.2, R905.2.7, R905.2.8.2 (Chapter 9) and Table R301.2 (Chapter 3). Check the edition and amendments adopted in your jurisdiction. codes
.iccsafe (opens in a new tab).org - City of Waterloo, Iowa, Ice Barrier Requirement (2021 IRC and the city's Table R301.2) cms6
.revize (opens in a new tab).com - City of Des Moines, Iowa, Residential Asphalt Shingle Requirements (2021 IRC) cms2
.revize (opens in a new tab).com - Maryland Department of Labor, Queen Anne's County Table R301.2(1) (amended 10-13-2020) dllr
.state (opens in a new tab).md .us - Owens Corning, Duration Series Shingles Installation Instructions (web page, checked October 21, 2026) owenscorning
.com (opens in a new tab) - The manufacturer's installation instructions for each product installed.
These guides document the scope of work a contractor performs. They aren't coverage or legal advice.