Roof Replacement in Kentucky: The One Layer That Can Stay

Central Roof Repair · Kentucky code

Kentucky’s code says a roof replacement comes off down to the deck. It writes exactly one exception, and both halves of that exception have to be true before anything stays on the sheathing.

Every October a few Central Kentucky homeowners get told that the ice shield at the eaves can stay on and the new roof goes over it. That is sometimes correct and sometimes a tear-off that was billed and not performed. The difference is one sentence of code, and it is short enough to read standing in the driveway.

Does a Kentucky roof replacement have to go down to the deck?

Yes. Section R908.3 of the Kentucky Residential Code states that roof replacement “shall include the removal of existing layers of roof coverings down to the roof deck.” One exception follows it.

That exception reads: “Where the existing roof assembly includes an ice barrier membrane that is adhered to the roof deck, the existing ice barrier membrane shall be permitted to remain in place and covered with an additional layer of ice barrier membrane in accordance with Section R905.” Kentucky’s residential code is the 2015 International Residential Code as adopted with state amendments, published by the Department of Housing, Buildings and Construction; which rulebook a particular job answers to is covered separately in which roof code applies in Lexington.

What are the two conditions inside that exception?

The membrane must be adhered to the deck, and a new layer of ice barrier must go over it. Fail either half and the exception does not apply — the old material comes off like every other layer.

The word doing the work is “adhered.” Section R905.1.2 permits an ice barrier to be built two different ways: “not fewer than two layers of underlayment cemented together, or a self-adhering polymer-modified bitumen sheet shall be used in place of normal underlayment.” Only one of those is bonded to the sheathing. A two-ply cemented underlayment assembly is cemented to itself, not adhered to the deck, so it falls outside the exception’s own wording. The self-adhering membrane — the peel-and-stick product most crews in Central Kentucky actually use at the eaves — is the one the exception describes.

The second half is just as literal. The existing membrane is permitted to remain “and covered with an additional layer of ice barrier membrane.” Not covered with underlayment. Not covered with shingles. An additional layer of ice barrier, installed in accordance with Section R905. A roof where the old peel-and-stick was left down and ordinary synthetic underlayment ran over the top of it has used half of a two-part permission.

How far up the roof does an ice barrier have to reach?

From the lowest edges of all roof surfaces to not less than 24 inches inside the exterior wall line. On roofs at 8:12 or steeper, it must also run not less than 36 inches measured along the slope from the eave edge.

Those are the dimensions in Section R905.1.2, and they matter to the replacement exception because the new layer has to be installed “in accordance with Section R905” — the same geometry, not a token strip. The section lists the coverings it applies to: asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, wood shingles and wood shakes. Its one exception is for “detached accessory structures not containing conditioned floor area,” which is why a detached garage and the house it sits behind can legitimately be detailed differently on the same property.

Whether an ice barrier is required on your roof at all is a separate question from how it is handled during a tear-off, and it turns on how the code’s climatic table treats Kentucky counties — we worked through that in is an ice barrier required on a Kentucky roof. This page assumes one is already on the deck and asks what the code lets a crew do with it.

What else cannot be reused on a replacement?

Rusted or deteriorated flashings and vents, and aggregate surfacing. Section R908.5 requires replacement of the first and flatly prohibits reinstalling the second.

The section’s words are specific: “Any existing flashings, edgings, outlets, vents or similar devices that are a part of the assembly shall be replaced where rusted, damaged or deteriorated,” and “Aggregate surfacing materials shall not be reinstalled.” Existing slate, clay or cement tile is permitted for reinstallation “except that damaged, cracked or broken slate or tile shall not be reinstalled.” Section R908.6 then requires flashings to be reconstructed in accordance with approved manufacturer’s installation instructions. The reinstallation rules get their own treatment in what Kentucky’s code lets a crew put back.

Worth separating from all of the above: none of this is the re-cover route. A new covering over an existing one is governed by R908.3.1, and R908.3.1.1 closes that route entirely where the existing roof is water soaked or deteriorated past serving as a base, where the existing covering is slate, clay, cement or asbestos-cement tile, or where the roof already carries two or more applications of any type — the detail is in when a roof re-cover is not allowed.

What can a homeowner actually check on tear-off day?

Three things, all visible from the ground or a phone photo: whether the retained layer is bonded, whether a new ice barrier is going over it, and whether the metal is being replaced or reused.

• Is the layer that stayed actually adhered? A self-adhered membrane does not lift at a corner and does not slide. If the retained material can be peeled back by hand or is clearly a cemented two-ply underlayment rather than a bonded sheet, the exception’s first condition is not met.
• Is the new layer over it an ice barrier, or underlayment? Ask which product is going down at the eaves and photograph the roll label before it is covered. The exception requires an additional layer of ice barrier membrane specifically.
• Is the old metal going back on? Drip edge, pipe boots, and vents that are rusted or deteriorated have to be replaced under R908.5, not reused because they are still in one piece.

A word on this as general craft rather than a story about any particular job: the eave detail is the one place on a residential roof where the code lets a legitimate shortcut and a disguised one look identical from the street. Both leave material on the deck. The difference is a bonded sheet with a new ice barrier over it versus whatever was easiest to leave down, and the only moment either can be verified is the few hours between tear-off and dry-in. That is why the photograph matters more than the conversation afterward.

Can a crew leave the old ice and water shield on during a full replacement?

Only under the single exception to Section R908.3, and only if both of its conditions are satisfied: the existing ice barrier membrane must be adhered to the roof deck, and it must be covered with an additional layer of ice barrier membrane in accordance with Section R905.

Does the exception let any other layer stay on the deck?

No. Section R908.3 requires removal of existing layers of roof coverings down to the roof deck, and the adhered ice barrier membrane is the only material its exception names. Reinstallation of specific existing materials is addressed separately in Section R908.5.

Which code edition is this?

The Kentucky Residential Code, which adopts the 2015 International Residential Code with Kentucky amendments and is published by the Kentucky Department of Housing, Buildings and Construction. Section numbers here were read from that publication on 23 October 2026. Your local building department administers it and can confirm the edition in force for a permit issued today.

This page quotes code text for general information and is not a code ruling, an inspection, or a substitute for your building department. No price, scope or outcome is implied.

By Central Roof Repair · Call or text (859) 310-1209.
Last updated 23 October 2026.