Updated October 2026 by Chris Horton. A method for reading the ice-and-water line on two roof bids against each other, not a verdict on any product, contractor or code question for your house. How we estimate costs
Two roof bids both say “ice & water shield.” One means a single strip along the gutters. The other means the eaves, every valley, the chimney and the sidewalls, and maybe a low-pitched porch roof covered edge to edge. Same words, same shingle brand, very different amounts of membrane on the deck. “Ice & water included” tells you a material is on the job. It does not tell you where it goes, how far it runs, what goes over the rest of the deck, or what the warranty language around it actually covers. This page turns that one line into something two bids can be compared on.
Is this the right decoder for your bids?
This page decodes one scope line: the self-adhered leak-barrier membrane, wherever a bid calls it ice and water shield, ice barrier, leak barrier, eave protection or peel-and-stick. It does not walk the rest of the roofing system. If you are comparing two asphalt shingle bids line by line, including tear-off, deck, flashing, ventilation and warranty tier, start with the architectural shingles quote decoder and come back here when the membrane line is the one that does not match. If one bid is for shingles and the other for metal, the asphalt vs metal roof quote decoder comes first, because the two bids are pricing different roof systems before membrane coverage even enters it.
If you have only one bid so far, the roof replacement quote checklist is the better starting point. If you have not decided whether the roof needs replacing, start with roof repair vs replacement.
What “ice and water shield” means on a bid
“Ice and water shield” is a trade nickname for a category of product: a self-adhering, polymer-modified bitumen sheet that bonds to the roof deck and seals around the nails driven through it. Manufacturers sell it under their own names. GAF, for example, calls its products leak barriers, and its StormGuard film-surfaced leak barrier is marketed for eaves and rakes, valleys, and the areas around chimneys and skylights on asphalt shingle and most metal roofs. Products in this category are typically tested to the ASTM D1970 standard, which is the standard the International Residential Code references for self-adhering membranes.
The membrane does not replace the rest of the underlayment. On most shingle roofs it covers the places most likely to leak, and a conventional underlayment covers everything else. That is why the line item on its own says so little. Two bids can both list the same membrane and still put it on very different parts of the roof.
Manufacturers named on this page are examples of documentation a bid can be checked against, not recommendations. Their instructions and warranty conditions apply to their own products only and change over time. The documents that settle a question about your roof are the current installation instructions for the exact products on your bid and the code your building department has adopted.
Where the membrane can go
A roof bid can place a self-adhered membrane in up to seven kinds of location. Each is a separate scope question, and a bid can include some and leave out others.
Eaves
The lowest edge of every roof plane, where ice dams form and meltwater can back up under shingles. This is the location most people mean by “ice and water,” and the one most likely to be tied to a code requirement. How far up the slope it has to run is its own question, covered in the eaves section below.
Valleys
Where two roof planes meet in a channel that carries water from both. GAF’s Timberline installation instructions show a full-width roll of GAF leak barrier centered in the valley for both open and closed valley construction, with the regular underlayment lapped over it. The IRC’s asphalt-shingle valley section has long permitted a self-adhering membrane complying with ASTM D1970 as the valley lining in place of the other listed lining materials. Permitted is not the same as required, so a bid can line valleys another way. It should say which.
Walls and chimneys
Where the roof meets a sidewall, a headwall above it, or the sides of a chimney. The same GAF instructions show leak barrier carried at least 5 inches up the wall at roof-to-wall intersections, and installed over the roof deck protection and at least 5 inches up the sides of a chimney, with metal flashing still doing the job of shedding water. The membrane at a wall is a backup behind the flashing, not a substitute for it. Flashing scope itself belongs to the architectural shingles quote decoder.
Penetrations
Skylights, pipe vents, exhaust hoods and other openings cut through the deck. Membrane around these is common on manufacturer product literature and rarely itemized on bids. A bid that says “ice and water at penetrations” should still say which ones.
Rakes
The sloped side edges of a gable. GAF’s StormGuard application instructions cover rake installation and the order it goes in: at the eave the drip edge goes on first and the membrane over it, while at the rake the membrane goes on first and the drip edge over it. Rake membrane is an option a bid may or may not include.
Low-slope sections
A porch roof, a shed dormer or any section pitched below 4:12. These sections have their own underlayment rules for shingles, and some bids answer them with membrane. See pitch and low-slope sections.
The full deck
Membrane over the entire roof instead of a conventional underlayment. This is a different assembly with its own conditions, not just more of the same line. See full-deck coverage.
Eaves: how far up the roof is “enough”?
There is no single national answer, and this page does not try to give one. What can be said is where the answer comes from and how to check whether a bid’s coverage matches it.
Where code applies, the jurisdiction decides
In the 2021 International Residential Code, section R905.1.2 requires an ice barrier for asphalt shingles and several other coverings only in areas with a history of ice forming along the eaves and causing water to back up, as designated in Table R301.2. Where it applies, the barrier is either two layers of underlayment cemented together or a self-adhering polymer-modified bitumen sheet, running from the lowest edges of all roof surfaces to a point at least 24 inches inside the exterior wall line of the building. On roofs pitched 8:12 or steeper, that edition adds that the barrier must also extend at least 36 inches measured along the slope from the eave edge. You can read the 2021 text as adopted in one state on ICC Digital Codes.
The key phrase is “as designated.” Table R301.2 is filled in by each adopting jurisdiction, and states and cities amend the rest. Massachusetts, for example, published an FAQ for its ninth-edition residential code explaining that it intended the ice barrier section to apply to one- and two-family homes and townhouses, and that same code text exempts detached accessory structures with no conditioned floor area. That is one state’s answer under one edition, not a rule for anywhere else. Editions differ, and so do local amendments. For your house, the position is whatever your building department says it is, which is why the right question for a contractor is “what does our jurisdiction require, and where is that on this bid?”
Manufacturers set their own installation minimums
Separately from code, a shingle or membrane manufacturer’s instructions say how its products go on. GAF’s Timberline instructions call for one layer of GAF leak barrier at eaves where ice dams can be expected, extending 24 inches beyond the inside wall line. The StormGuard instructions say to install up the roof to a point at least 24 inches past the interior warm wall. These are installation instructions for those products, not code, and other manufacturers write their own.
Notice that the two reference points are not identical. The 2021 IRC measures from the exterior wall line. GAF’s documents measure from the inside or interior warm wall. The difference is the thickness of the wall. A bid that says “24 inches past the wall” should say which wall line it means.
Why one course of membrane often falls short
The distance that matters is measured from the eave edge, across the overhang, past the wall line, and up the slope. Membrane rolls are installed along the slope, so pitch stretches the distance. StormGuard rolls, for example, are 36 inches wide according to GAF’s data sheet, and its instructions require a second course to overlap the first by at least 3 inches, so two courses cover about 69 inches of slope. The table below is plain geometry, not a code interpretation: it converts a horizontal run of the overhang plus 24 inches into inches along the slope.
| Horizontal overhang, eave edge to exterior wall | Along the slope at 4:12 | At 6:12 | At 8:12 | At 12:12 |
|---|---|---|---|---|
| 12 inches (+ 24 inches past the wall line) | About 38 in | About 40 in | About 43 in | About 51 in |
| 18 inches (+ 24 inches) | About 44 in | About 47 in | About 50 in | About 59 in |
| 24 inches (+ 24 inches) | About 51 in | About 54 in | About 58 in | About 68 in |
Every figure in the table is longer than one 36-inch course. If the reference is an interior wall rather than the exterior wall line, add the wall’s thickness. So “one row of ice and water at the eaves” and “two courses at the eaves” are not the same scope, and a bid that says only “ice and water at eaves” has not told you which one you are buying. Ask for the number of courses or the distance up the slope, and the wall line it is measured from.
Pitch and low-slope sections
Pitch changes the membrane question in two ways: steep slopes stretch the eave measurement, as above, and shallow slopes bring in their own underlayment rules.
Under the IRC, asphalt shingles may be used only on slopes of 2:12 or more, and slopes from 2:12 up to 4:12 call for double underlayment. GAF’s Timberline instructions use the same band. For slopes from 2:12 to less than 4:12 they call for the whole deck to be covered with two layers of GAF roof deck protection, plus one layer of GAF leak barrier at eaves where ice dams can be expected, or two plies of roof deck protection at the eaves where ice or debris dams are not expected. At 4:12 and above, the instructions drop to one layer of roof deck protection, again with leak barrier at the eaves where ice dams can be expected.
That makes a roof section at 3:12 or 3.5:12 a different underlayment job from the main roof at 6:12, even when the bid prices the whole house as one roof. A complete bid identifies the low-slope sections and says how each will be underlaid: two layers of underlayment, a self-adhered membrane over the whole section, or something else. If a bid proposes membrane over a low-slope section in place of the manufacturer’s two-layer method, that may be a reasonable choice, but whether it satisfies both the shingle manufacturer’s instructions and your local code is a question with a document behind it. Ask the contractor to name that document.
Below 2:12, GAF’s instructions say its shingles must not be used at all. A section that flat needs a low-slope roofing system, which is a different scope, and a bid that shingles it needs an explanation before anything else is compared.
Full-deck coverage: a different assembly, not just more membrane
Some bids propose self-adhered membrane over the entire deck. It is neither automatically better nor automatically wrong, and some jurisdictions call for it. What makes it different is that it changes how the roof deck handles moisture, and manufacturers attach conditions to it.
GAF’s technical bulletin TAB-R-111 sets out both sides. On the plus side, a fully adhered membrane that seals around nails reduces leak vulnerability, and GAF says full-deck coverage under fiberglass asphalt shingles helps in severe wind and hail. On the other side, GAF describes leak barriers as vapor retarders that stop moisture-laden air from the attic passing out through an otherwise permeable roof, and warns that full-deck coverage can cause moisture problems in the attic unless critical precautions are taken. Its stated precaution is ventilation, with a design professional addressing the risk of trapped moisture and condensation for the specific building.
A second bulletin, TAB-R-175, dated May 2026, says full-deck coverage may be required by a local or state code, or be one of a limited number of options it allows. It also explains how full-deck coverage changes GAF’s accessory list for its WindProven limited wind warranty: LayerLock shingles plus GAF starter strips at eaves and rakes, ridge cap shingles, a WeatherWatch or StormGuard leak barrier, and attic ventilation. GAF says the ventilation requirement can be waived only where the structure’s design or a sealed attic prevents ventilation, and that issues arising from a lack of proper ventilation are not covered under any GAF limited warranty.
Jurisdictions do write this into code. GAF’s bulletin on Connecticut’s residential code requirements, for example, describes an amended underlayment section with an exception that lets the entire deck be covered with self-adhering membrane, and stresses ventilation and moisture control where that route is used. That is one state’s code and one manufacturer’s reading of it.
So when one bid is partial coverage and the other is full deck, they are not comparable on total until both answer the same questions: why full deck is proposed, whether your jurisdiction requires it, how the attic is ventilated or otherwise designed for it, and which warranty document the assembly is meant to qualify for. None of that is a judgment that full deck is right or wrong for your house. It is the information that makes the two prices about the same thing.
The ice & water coverage decoder matrix
Read each bid into the matrix line by line. For each line, give each bid a status using the same five words the architectural shingles decoder uses: Included, Reused, Allowance, Excluded, or Unspecified. The last column is the point of the exercise. Until both bids state that line, a difference in totals may be a difference in membrane scope rather than a difference in price.
| Line | A complete bid states | Wording that hides it | Not comparable until both bids state |
|---|---|---|---|
| Eaves coverage | Membrane at all eaves, the distance up the slope or the number of courses, and the wall line it is measured past. | “Ice & water at eaves.” “Per code.” | The distance or course count, and what requirement it is meant to meet. |
| Valleys | Membrane in every valley, full width and full length, or the other valley lining used instead. | “Valleys protected.” | Which valleys get membrane and which get something else. |
| Penetrations | Which chimneys, skylights, pipes and vents get membrane around them. | “Around penetrations as needed.” | A list, or a statement that all penetrations are included. |
| Walls and transitions | Membrane at sidewalls, headwalls and chimney sides, and how far up the wall, with the flashing scope stated separately. | Silent, or folded into “flash as needed.” | Whether membrane is at each wall intersection, separately from flashing. |
| Rakes | Whether membrane runs along the rake edges. | Silent. | Included or excluded, in so many words. |
| Low-slope sections | Which sections are below 4:12, and how each is underlaid: two layers, full membrane, or a different roof system below 2:12. | One pitch and one price for the whole house. | The method for each low-slope section. |
| Full-deck coverage, if proposed | Why it is proposed, whether it is required locally, and the ventilation or moisture-control design that goes with it. | “Full ice & water upgrade.” | Both bids price the same coverage, or the full-deck bid states the conditions it depends on. |
| Membrane product identity | Manufacturer and product name. | “Premium ice & water.” “Peel-and-stick.” | A named product that can be checked against its instructions and data sheet. |
| Underlayment combination | The named underlayment over the rest of the deck, and how it laps the membrane. | “Synthetic underlayment.” | What covers the deck where the membrane stops. |
| Deck-preparation assumptions | That membrane goes on a dry, swept deck after old material and fasteners are removed, what happens to water-damaged sheathing, and how plank decks and masonry are handled. | Silent, or a deck line with no unit price. | How damaged sheathing under the membrane is found, priced and approved. |
| Accessory and system requirements | Whether the membrane is from the shingle manufacturer, and which system accessories, including ventilation, the bid relies on. | “System install.” | The accessory list each bid’s warranty claim depends on. |
| Warranty-related language | Which document covers the membrane, which covers the roof system, and which covers workmanship, by name. | “Lifetime protection.” “Fully warrantied.” | The named warranty documents, attached or linked. |
| Installer-defined exclusions | What the contractor will not cover with membrane, and what is left to an owner decision. | Fine print such as “membrane at contractor’s discretion.” | Exclusions written out on both bids. |
A bid that fills every line is not necessarily the better bid. It is a bid you can now compare. Once both are read into the matrix, the compare roof quotes tool and the roof quote analyzer walk the rest of the roof the same way.
Ask before signing
Vague phrases are not necessarily bad faith. They are often shorthand a crew understands and a homeowner does not. Converting them into specific questions, in writing, to every contractor makes the answers comparable too.
Three scope patterns homeowners ask about
These examples are drawn from homeowner and roofer discussions we read while preparing this page. They are anecdotal illustrations of how membrane scope differs between bids. They are not benchmarks for what is typical, required or fair, and we have left out any prices mentioned.
“One bid says ice and water. The other says six feet at the eaves plus valleys.”
The second bid has stated a distance and a second location. The first has stated a material. Before comparing totals, ask the first contractor for the same two facts. At a 36-inch roll width with a 3-inch lap, six feet is roughly two courses, and the geometry table shows why a single course often does not reach 24 inches past the wall line.
“The back porch is about 3.5:12. One roofer wants membrane on all of it, the other didn’t mention it.”
A 3.5:12 section sits inside the 2:12 to 4:12 band where both the IRC and GAF’s shingle instructions call for a different underlayment method than the main roof. The bid that is silent has not answered the question yet, which does not make the other bid right either. Ask both how the section will be underlaid and which document they are following.
“We were offered full-deck ice and water as a warranty upgrade.”
Full-deck coverage and warranty eligibility are separate questions. Ask whether it is required here, how the attic is ventilated, and which warranty document names the assembly. Then compare it with a bid priced on the same coverage, not with a partial-coverage total.
Reading the warranty language around the membrane
Three different promises can sit next to a membrane line, and bids often blur them.
- The membrane’s own product warranty. GAF’s data sheet, for example, says StormGuard is eligible for a lifetime limited warranty when installed with GAF lifetime shingles and at least two additional qualifying GAF accessories, with shorter coverage in other combinations. That covers the product under that document’s terms, not the whole roof.
- A manufacturer roof system warranty. GAF’s Roofing System Limited Warranty counts a leak barrier as one of the qualifying accessories that can make up its required set. Whether your bid’s membrane counts toward a system tier depends on the exact products, the tier and the installer, so ask which tier the bid is built to.
- The contractor’s workmanship warranty. This is the contractor’s promise about installation, on the contractor’s own terms. It is the one most likely to matter if membrane was installed in the wrong place or not at all.
Two cautions keep this from being overstated. First, a membrane from a different manufacturer than the shingles does not by itself mean a warranty is void. It may mean it does not count toward a particular system tier, which is a narrower thing, and the document for that tier is what decides. Second, compatibility is a real issue: GAF’s StormGuard instructions warn that incompatible leak barriers can soften and drip, and say GAF is not responsible for damage caused by incompatibility with leak barriers it did not make. Ask the contractor to confirm the membrane, shingles and any sealants are approved to be used together.
If the old roof already has membrane bonded to the deck, the bid should also say whether it comes off. Where the 2021 IRC applies, an existing ice barrier membrane that is adhered to the deck can stay on a reroof if it is covered with an additional layer of ice barrier membrane, as described in the 2021 IRC reroofing provisions. A bid that leaves it in place and a bid that strips it are different scopes.
Route the decoded membrane scope into the roofing tools
- Compare roof quotes takes two or three normalized bids and flags where they say different things.
- Roof quote analyzer steps one bid through a series of passes and writes the follow-up questions out.
- Roof estimate scope checker is a quick pass for the lines a bid is most likely to leave blank, membrane included.
- Before you sign: roofing checklist collects the last questions to settle before a contract.
- Roof replacement cost explains the drivers behind a total once the bid defines the work, and the roof replacement cost calculator works through them for your roof without inventing a number for it.
- The roofing warranty guide explains manufacturer and workmanship coverage, and the Roofing hub has everything else.
What this page deliberately does not do
It does not publish a price per square, per roll or per foot for membrane, and it does not repeat prices homeowners have posted online as if they were market facts. Roof size and pitch, the number of eaves, valleys and walls, the product, the deck condition and local labor all move the cost of this line, and the number that matters is the one on a bid that states the coverage.
It does not map code requirements state by state or say any coverage is required everywhere. Code text is quoted from named editions as examples, and the requirement for your roof is set by the code your jurisdiction has adopted and amended. It does not rank membrane brands or contractors, and it does not cover insurance or storm claims, which follow different rules.
Common questions
Is ice and water shield required on every roof?
No single answer covers the country. In the 2021 IRC, an ice barrier is required in areas the jurisdiction designates as having a history of ice damming, and states and cities adopt and amend that differently. Manufacturer instructions can call for membrane in places code does not, as instructions for those products. Ask your contractor what your jurisdiction requires and where the bid puts the membrane.
Is more ice and water always better?
Not automatically. More membrane at eaves, valleys and walls is a real scope difference you can weigh. Full-deck coverage is a different assembly: GAF describes leak barriers as vapor retarders and ties full-deck coverage to ventilation and moisture-control design. Whether it suits your house is a question for the building’s design, not a rule of thumb.
My bid says “ice and water per code.” Is that enough?
It is enough to start a question, not to compare bids. Ask which code edition and section apply, what that means for your house, and for the resulting coverage to be written on the bid as locations and distances.
How far up from the gutter should it go?
Where the 2021 IRC ice-barrier provision applies, at least 24 inches inside the exterior wall line, with an extra 36-inch along-slope minimum on roofs at 8:12 or steeper. GAF’s instructions for its products say 24 inches past the inside wall line. Because the distance is measured past the wall and up the slope, the membrane run is usually longer than one 36-inch course.
Does the membrane have to be the same brand as the shingles?
For basic installation, not necessarily, though compatibility matters and manufacturers warn about it. For some manufacturer system warranty tiers, the leak barrier may need to be that manufacturer’s product to count toward the required accessories. Ask which tier the bid is built to and check that tier’s document. If both bids name GAF Timberline HDZ, the Timberline HDZ quote decoder lists which GAF accessories each GAF warranty document counts.
About the author
Chris Horton writes UpgradeWorth’s homeowner decision guides. He covers how replacement projects are scoped, quoted and warrantied, with a bias toward what a homeowner can verify in writing rather than what a salesperson says at the kitchen table. UpgradeWorth does not sell leads, rank contractors or accept placement fees.
Next: comparing two complete shingle bids? Use the architectural shingles quote decoder. Weighing shingles against metal? The asphalt vs metal roof quote decoder covers that. Only one bid so far? Start with the roof replacement quote checklist. Everything else is at the Roofing hub.