Metal Roof Over Wood Shake: Kentucky Code R908.4

Central Roof Repair · Kentucky Law & Your Roof

Putting a metal roof over wood shake under Kentucky code is allowed — but only on one condition, and it is a fire condition, not a structural one. If the new metal creates a combustible concealed space, the entire old surface has to be covered first.

Older houses across Madison, Estill, Powell and Clark counties still carry wood shingle or shake under something newer. When a homeowner asks whether metal can go straight over it, the honest answer comes from two sections of the residential code that have to be read together — and the second one is the one almost nobody quotes. This is the companion to the question of when a roof re-cover is not allowed at all under R908.

Does Kentucky code allow metal over wood shake?

Yes, with a condition. Section R908.3.1 permits metal panel, metal shingle, and concrete and clay tile roof coverings over existing wood shake roofs “where applied in accordance with Section R908.4.”

That cross-reference is the whole rule. R908.3.1 lists the situations where installing a new roof covering over an existing one is permitted, and the wood-shake entry does not stand alone — it is permission conditioned on another section. Kentucky gets there through regulation: 815 KAR 7:125, promulgated under KRS 198B.040(7) and 198B.050, provides that the 2015 International Residential Code for One and Two Family Dwellings “shall be the mandatory state residential building code for all single-family dwellings, two (2) family dwellings, and townhouses.” The adopted code document itself is published by the Kentucky Department of Housing, Buildings and Construction.

What does R908.4 actually require?

Where the new roof covering over wood shingle or shake creates a combustible concealed space, the entire existing surface must be covered with gypsum board, mineral fiber, glass fiber or other approved materials, securely fastened in place.

Three words in that sentence do the work. Entire — not the valleys, not the eaves, the whole surface. Securely fastened — it is an installed layer, not a loose-laid one. And combustible concealed space — which is what you create the moment metal panels sit on battens or a furring system above old shake, leaving an air gap between a combustible deck covering and the new metal.

That is why the rule reads as a reroofing requirement but behaves like a fire requirement. The gap is the hazard; the gypsum, mineral fiber or glass fiber layer is the separation. The approved-materials phrase also means the code official has the final say on a substitute, which is a conversation to have before the material is on the truck.

The three conditions that stop a re-cover regardless

Section R908.3.1.1 bars a roof re-cover outright in three situations, and satisfying R908.4 does not rescue any of them.

• Where the existing roof or roof covering is water soaked, or has deteriorated to the point that it is not adequate as a base for additional roofing.
• Where the existing roof covering is slate, clay, cement or asbestos-cement tile.
• Where the existing roof has two or more applications of any type of roof covering.

The third one catches a lot of Central Kentucky houses. Shake, then asphalt over the shake in the 1980s, now metal proposed on top: that is already two applications, and the answer is a tear-off to the deck under R908.3, which requires roof replacement to include removal of existing layers down to the roof deck. R908.3 carries one exception — where the existing assembly includes an ice barrier membrane adhered to the roof deck, that membrane is permitted to remain in place and be covered with an additional layer of ice barrier membrane. That is also when roof decking replacement stops being hypothetical, because the condition of the deck is finally visible.

What cannot be reinstalled on a Kentucky reroof

Section R908.5 allows existing slate, clay or cement tile to be reinstalled, except that damaged, cracked or broken pieces shall not be reinstalled. Two items are harder rules: any existing flashings, edgings, outlets, vents or similar devices that are part of the assembly shall be replaced where rusted, damaged or deteriorated — and aggregate surfacing materials shall not be reinstalled at all.

Section R908.6 adds that flashings shall be reconstructed in accordance with approved manufacturer’s installation instructions, and that metal flashing to which bituminous materials are to be adhered shall be primed prior to installation. Priming before adhesion is a one-line requirement that explains a large share of the flashing failures we are called out to look at on metal roof seam and flashing repair.

The one thing reroofing is excused from

Slope. Section R908.1 states that reroofing is not required to meet the minimum design slope of one-quarter unit vertical in 12 units horizontal (2-percent slope) required by Section R905, for roofs that provide positive roof drainage.

The same exception adds that on a roof with positive drainage, re-covering or replacing a roof covering does not require the secondary emergency-overflow drains or scuppers of Section R903.4.1 to be added to an existing roof. Both exceptions hinge on the phrase “positive roof drainage” — if the roof ponds, neither applies, and R908.2 still requires the structural roof components to be capable of supporting the roof covering system plus the material and equipment loads encountered during installation.

How this reads in the field

Metal over shake is usually proposed to avoid a tear-off, and the tear-off is usually the thing that should happen. Once you add the R908.4 separation layer across the entire surface and fasten it, you have bought material and labour that narrow the savings — and you still own whatever the old shake is hiding. The counting exercise comes first on any older roof: how many layers are actually up there, and does the deck read solid from the attic side. That count decides which section of R908 you are in before anybody prices anything. We quote from what the roof turns out to be, not from what the first look suggested.

Does a standing-seam metal system change the answer?

R908.3.1 treats complete and separate roofing systems, such as standing-seam metal roof systems, that are designed to transmit roof loads directly to the building’s structural system and do not rely on existing roofs and roof coverings for support, as not requiring removal of existing roof coverings. The combustible-concealed-space requirement of R908.4 is a separate question and is triggered by the concealed space, not by the attachment method.

Is gypsum board the only approved separation material?

No. R908.4 names gypsum board, mineral fiber, glass fiber “or other approved materials securely fastened in place.” “Approved” in code language means acceptable to the code official for the jurisdiction, so a substitute is a question to settle with that office in advance.

Which code edition applies to my Kentucky house?

815 KAR 7:125 Section 2 makes the 2015 International Residential Code the mandatory state residential code for single-family and two-family dwellings and townhouses, except as provided in that section’s own subsection (2). Kentucky publishes the adopted code with state amendments; your local code official applies the edition in force for your permit.

Last updated October 20, 2026.

By Central Roof Repair · Call or text (859) 310-1209.