Quick answer
Ice and water shield is a self-adhering, rubberized asphalt membrane laid directly on the roof deck under the roof covering, where it seals around nails and blocks water that ice dams or wind-driven rain push back under the shingles.
Ice & Water Shield is a Grace product name 2 now used for the whole category; the building code calls it an ice barrier and requires one at the eaves where ice damming is a recorded local hazard.
Quick facts
- Code name
- Ice barrier, IRC R905.1.2 4
- Required where
- Local history of ice forming along the eaves (your jurisdiction's Table R301.2) 4
- How far
- From the lowest roof edge to at least 24 in inside the exterior wall line 4
- What qualifies
- A self-adhering polymer-modified bitumen sheet, or two layers of underlayment cemented together 4
- Covers under
- Asphalt shingles, metal shingles, roll roofing, slate, wood shingles and shakes 4
- Exempt
- Detached accessory buildings with no conditioned space 4
Key takeaways
- Ice and water shield is a sticky, rubbery membrane laid on the roof deck under the shingles at the places leaks start.
- It seals around nails, which ordinary underlayment does not, so trapped water cannot get through.
- Where your area has a history of ice dams, the code requires an ice barrier from the roof edge to 24 inches inside the outside wall.
- Measured along the slope, that is often 4 feet or more of membrane on a house with an overhang.
- It handles the water from an ice dam; insulation and attic ventilation are what stop the dam forming.
What it is made of
Ice and water shield comes in rolls. One product's Florida approval describes it as a rubberized asphalt adhesive backed by a layer of high-density, cross-laminated polyethylene 2. In plain words: a thick, sticky asphalt layer with a tough plastic film on top. A paper release sheet covers the sticky side until it is laid.
The roofer peels off the release sheet and presses the membrane onto the clean, dry roof deck, where it bonds. Shingles or other roofing then go on top and are nailed through it into the deck.
How it works
Shingles shed water that runs downhill. They are not watertight against water that sits or flows uphill. An ice dam at the eave traps meltwater behind it, and that pond can creep up under the shingle laps. Ice and water shield is the layer that stops it reaching the deck.
Products sold as ice and water shield are self-adhered underlayments made to ASTM D1970, the standard for self-adhering polymer-modified bitumen sheets for ice dam protection 2. Two properties do the work.
The membrane bonds to the deck over its whole surface, so water cannot travel underneath it. And the rubberized asphalt closes tightly around every nail driven through it, so the fastener holes that would leak through ordinary felt stay sealed.
Why ice dams happen in the first place
An ice dam is a ridge of ice along the bottom edge of the roof. According to the shingle makers' trade association, it is usually caused by snow that melts and refreezes again and again, or by frozen slush backing up in the gutters 3.
The usual chain goes like this. Heat leaks from the house into the attic. The warm attic melts the snow on the upper roof.
The meltwater runs down to the eave, which sits over the cold overhang, and freezes there. Each melt adds more ice, and the dam grows.
Water then pools behind the dam, and that pond is what finds its way under the shingles.
The association's advice for stopping dams is to keep the attic cold: insulate it from the warm house and ventilate it properly, with baffles at the eaves so the air can flow 3. Ice and water shield is the backup for when a dam forms anyway.
- Heat leaks into the atticFrom the rooms below
- Snow on the upper roof meltsThe warm deck melts it from below
- Meltwater reaches the cold eaveThe overhang sits outside the warm house
- It refreezes into a ridgeEach melt adds more ice 3
- Water pools behind the damAnd can back up under the shingles
Source: [3]
The chain shows why the shield is a backup: it handles the last step, while a cold attic stops the first.
Types: the two ways to meet the code
The code accepts two kinds of ice barrier 4. Roofers today almost always use the first.
| Type | What it is | Notes |
|---|---|---|
| Self-adhering membrane | A polymer-modified bitumen sheet that sticks to the deck | One layer is enough; sold under many brand names, made to ASTM D1970 2 |
| Two cemented layers | Two layers of regular underlayment glued together with roofing cement | Older method; more labor |
On low-slope shingle roofs, between 2/12 and 4/12, the shingle makers' association also allows a single layer of self-adhering underlayment in place of the usual double layer of felt, following the maker's requirements 5.
Worked example: how far up the roof it has to go
The 24 inches is measured horizontally inside the wall, not along the deck from the roof edge. On a house with a 2-foot overhang and a 6/12 pitch:
| Part | Horizontal distance | Along the 6/12 slope |
|---|---|---|
| Overhang, edge to wall line | 24 in | 26.8 in |
| Code minimum inside the wall line | 24 in | 26.8 in |
| Total from the roof edge | 48 in | 53.7 in |
Ice barrier reach ≥ eave overhang + 24 in. inside the exterior wall line
eave overhang- From the roof's lowest edge back to the outside face of the wall
24 in.- The 2021 IRC minimum past the wall line 4
Measured on the roof plane, a roll may need to run farther than this on steep or wide overhangs. Your code office can add more.
Source: [4]
The membrane must run about 54 inches up the slope, more than one 3-foot-wide course of membrane. A quote that says "one row of ice and water at the eaves" would fall short on this house. Deeper overhangs and steeper pitches push it further. Slope length = horizontal × 1.118 at 6/12.
Where else roofers use it
Beyond the code minimum at the eaves, roofers and shingle manufacturers commonly specify self-adhered membrane in the places water concentrates: valleys, around chimneys and skylights, along sidewalls where step flashing is installed, and around plumbing vents. In hurricane-prone areas some roofers apply it over the whole deck as a secondary water barrier.
The shingle makers' trade association recommends the membrane run at least 24 inches inside the interior wall line 3, a little further than the code's exterior wall line. Check the shingle manufacturer's installation instructions: they set the warranty conditions, and some ask for more coverage than the code.
Valleys, chimneys and skylights
Eaves are where the code requires an ice barrier, but they are not the only places water collects on a roof. A valley, where two roof planes meet in an inside corner, carries the water from both planes at once.
A chimney or skylight blocks the flow, so water piles up on its uphill side. A sidewall where the roof meets a wall can let wind-driven rain in behind the flashing.
These spots are where roofers most often add self-adhered membrane beyond what the code asks for. It sits under the valley lining or flashing as a second line of defense.
On your quote, look for the membrane listed for each of these areas, not only "at eaves". If it is missing, ask whether the roofer simply left it off the paperwork or does not plan to install it.
Benefits
- Seals around nails, unlike felt or synthetic underlayment
- Stops ice-dam backup and wind-driven rain at the edges
- Meets the code ice-barrier requirement in a single layer
Limitations
- It does not stop ice dams forming. A warm attic still melts the snow.
- It traps moisture if a poorly ventilated deck is covered with it everywhere.
- It sticks hard, so the next reroof usually means replacing or scraping that part of the deck.
- It cannot go over an old roof; the old roofing must come off first 2.
- It is not made for long sun exposure and must be covered within the product's time limit.
What to check on your quote
- The distance up the roof it will run at the eaves, and whether it was measured inside the wall line
- Whether it is included in valleys and around chimneys, skylights and sidewalls
- The product name, so you can check it is a self-adhering polymer-modified bitumen sheet
- Whether it is priced per square or per linear foot of eave
How it is installed: the details that matter
One product's Florida approval lists conditions that are typical of these membranes 2. Your product's own instructions are the ones that apply.
- The deck must be clean, dry and free of debris, with any raised nails fixed first.
- It is laid in rows parallel to the eave, starting at the eave, each row lapping the one below so water runs off it.
- It is not installed over an existing roof covering; the old roof comes off first.
- The roof covering is nailed through it into the deck, not glued to it.
- It may be left exposed on the deck for a limited time only (30 days for that product) before the roofing goes on.
Keeping it working: attic airflow
An ice barrier only handles the water.
Stopping the dam is the attic's job, and the code has a rule here that is easy to break by accident: there must be at least a 1-inch air space between the insulation and the roof deck at the vents, and insulation must not block the free flow of air 1.
When blown-in insulation is piled out to the edge of the attic, it can bury the soffit vents. Nothing looks wrong from inside, but the cold air no longer reaches the underside of the roof. If you are getting ice dams, check the attic airflow with our vent area calculator before blaming the roofing.
Signs of ice-dam damage to look for
- Thick ice along the eaves and long icicles after a snowfall
- Water stains on ceilings or walls near the outside walls, often appearing during a thaw
- Wet or matted insulation along the edges of the attic
- Peeling paint or soft wood on the fascia and soffit
- Mold or a musty smell in the attic near the eaves
Safety and risk
Do not chip or chop ice from a ladder or the roof. It damages shingles and falls are common in winter. A roofer or ice-dam service does that work.
If you see these, have the roof edge and attic checked. A roof inspection can find wet deck before it rots. Do not climb onto an icy roof to chip ice off.
What the code requires
The International Residential Code ties the requirement to local climate, not to a national map. Your building department records whether ice damming is a local hazard in its own Table R301.2.
| Question | What the code says |
|---|---|
| When | In areas with a history of ice forming along the eaves causing a backup of water, as designated in Table R301.2 |
| Under which coverings | Asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles and wood shakes |
| Material | Not fewer than two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet |
| Extent | From the lowest edges of all roof surfaces to a point at least 24 inches inside the exterior wall line |
| Exception | Detached accessory structures that contain no conditioned floor area |
Sources: [4]
Ice and water shield vs regular underlayment
| Ice and water shield | Felt or synthetic underlayment | |
|---|---|---|
| What it is | Self-adhering rubberized asphalt sheet (ASTM D1970) 2 | Asphalt-soaked felt or a woven plastic sheet |
| How it is attached | Sticks to the deck over its whole surface | Nailed or stapled to the deck |
| Seals around nails | Yes | No |
| Counts as the code ice barrier | Yes, in one layer 4 | Only as two layers cemented together 4 |
| Where it is used | Eaves, valleys, around chimneys and other weak spots | The rest of the roof deck |
Common misconceptions
- Myth One row at the eave is always enough.
- Reality The code measures 24 inches inside the exterior wall line. With an overhang, that often needs more than one 3-foot course.
- Myth Ice and water shield prevents ice dams.
- Reality It stops the water from a dam getting in. A cold, well-ventilated attic prevents the dam.
- Myth More membrane is always better.
- Reality Covering a whole deck can trap moisture if the attic is poorly ventilated. Follow the shingle maker's instructions.
- Myth "Ice and Water Shield" is the code term.
- Reality It is a product name. The code calls it an ice barrier and accepts any product that meets the rule.
Is it required where you live?
The code does not draw an ice-dam map. It leaves the decision to each jurisdiction, which records in its own climate table, Table R301.2, whether ice damming is a local hazard 4.
If your building department marks it "yes", the ice barrier is required on shingle, slate, wood and metal-shingle roofs. If "no", it is optional.
Our study of where the ice barrier line falls reads that rule edition by edition and compares how different jurisdictions answer it. Your building department has the final word for your address.
What to ask before your reroof
- Does our area require an ice barrier, and how far up from the eave will you run it?
- Did you measure the 24 inches inside the exterior wall line, including the overhang?
- Will you also use membrane in the valleys and around the chimney and skylights?
- Which product is it, and does the shingle maker's warranty call for more coverage?
- Have you checked that the attic insulation is not blocking the soffit vents?
Keep going
- The ice barrier lineOur edition-by-edition study of R905.1.2 and where it applies
- Roof replacementIce barrier is installed at the deck stage
- Ventilation calculatorVentilation is what prevents ice dams
- Roof inspectionFinding ice-dam damage before it rots the deck
Questions about ice and water shield
Is ice and water shield required by code?
Only where your jurisdiction records a history of ice forming along the eaves. In those areas the IRC requires an ice barrier from the roof edge to at least 24 inches inside the exterior wall line under shingles, slate, wood and metal shingles. Ask your building department, or check its Table R301.2.
How far up the roof should ice and water shield go?
At least 24 inches inside the exterior wall line, measured from the lowest roof edge. With an overhang, that is more than 24 inches along the deck; a 2-foot overhang at 6/12 needs about 54 inches of membrane up the slope.
Can you put ice and water shield on the whole roof?
Some roofers do, especially in hurricane regions. The trade-off is moisture: a fully sealed deck cannot dry through the underlayment, so it depends on good attic ventilation. Follow the shingle manufacturer's instructions so the warranty holds.
Is ice and water shield the same as underlayment?
It is a type of underlayment, a self-adhering one. Ordinary felt or synthetic underlayment is mechanically fastened and does not seal around nails, so it cannot serve as the code ice barrier on its own unless two layers are cemented together.
Does ice and water shield stop ice dams?
No. It stops the water an ice dam traps from getting into the house. Ice dams form from repeated thawing and refreezing of snow at the eaves; keeping the attic cold with insulation and ventilation is what prevents them.
Can ice and water shield be left uncovered?
Only for a short time. These membranes are not made to sit in the sun for long. One product's Florida approval limits exposure on the deck to 30 days before the roofing goes on. Check the time limit for the product on your roof.
Does ice and water shield go over or under the drip edge?
At the eaves it goes over the drip edge, because the code requires underlayment to be installed over the drip edge along eaves. At the rakes the drip edge goes on top. That way water always runs from one layer down onto the next.
Do I need ice and water shield in a warm climate?
The code only requires an ice barrier where ice damming is a recorded local hazard. In warm areas it is optional, but many roofers still use self-adhered membrane in valleys and around chimneys and skylights, where water collects and wind-driven rain gets in.
Sources
- International Code Council, 2021 International Residential Code §R806.3 Vent and insulation clearance (read at UpCodes), retrieved .
- Florida Building Commission product approval FL298-R9, evaluation report for Grace VYCOR Ice & Water Shield (CREEK Technical Services, March 20, 2024), retrieved .
- Asphalt Roofing Manufacturers Association, "Protecting Against Damage from Ice Dams" (Aug 27, 2024), retrieved .
- International Code Council, 2021 International Residential Code §R905.1.2 Ice barriers (Maryland adoption, read at UpCodes), retrieved .
- Asphalt Roofing Manufacturers Association, "Installation of Asphalt Shingles on Lower Sloped Roofs" (July 14, 2025), retrieved .
Expert review
Written by the HyreRoof editorial team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Code text read verbatim in the 2021 IRC as adopted in Maryland; slope lengths calculated from the 6/12 multiplier.
Suggest a correction. We fix errors and say what changed.