Wood Shake and Shingle Code in Georgia

Shakes vs. Shingles: Two Products, Two Code Sections, Different Requirements

Georgia code treats wood shakes and wood shingles as distinct roofing materials, each governed by its own IRC section. Understanding which product you are installing determines the slope minimum, interlayment requirements, and exposure limits your contractor must follow.

IRC R905.7 governs wood shingles. A wood shingle is sawn on both faces, producing a smooth, uniform, tapered piece. Cedar shingles grade under ASTM standards as No. 1 (Blue Label), No. 2 (Red Label), or No. 3 (Black Label). No. 1 shingles consist of 100% edge grain heartwood with no defects. No. 2 permits limited flat grain and minor defects. No. 3 allows additional sapwood and defects and is suitable for starter courses and undercourse applications. For exposed roofing, specify No. 1 or No. 2 exclusively.

IRC R905.8 governs wood shakes. A wood shake is split on at least one face, creating a rough, textured surface with natural grain variation. Shakes are thicker than shingles (typically 1/2 to 3/4 inch at the butt end versus 3/8 to 1/2 inch for shingles) and carry a more rustic appearance. The Cedar Shake and Shingle Bureau grades shakes as No. 1 (Premium), No. 2 (Standard), and No. 3 (Utility). For residential roofing, No. 1 Premium is the standard specification.

Both products come from western red cedar, Alaskan yellow cedar, or pressure-treated southern pine. Western red cedar dominates the market due to its natural resistance to decay and insect damage. The natural oils in cedar heartwood act as a preservative, giving untreated cedar a 20 to 30 year lifespan in Georgia's climate. Factory-applied preservative treatments extend that lifespan to 30 to 40 years.

For homeowners in Buckhead and Sandy Springs considering wood roofing, the choice between shakes and shingles is primarily aesthetic. Shingles deliver a smooth, tailored appearance. Shakes create a more textured, natural look. Both carry significant code requirements that your contractor must follow.

Minimum Slopes: 3:12 for Shingles, 4:12 for Shakes

Georgia code sets different minimum slopes for the two wood roofing products. Wood shingles under IRC R905.7 require a minimum slope of 3:12 (three inches of rise per twelve inches of run). Wood shakes under IRC R905.8 require a steeper 4:12 minimum. The difference reflects the products' water-shedding characteristics.

Wood shingles, with their smooth sawn surfaces, lay tight against each other and shed water at lower slopes. Shakes, with their rough split surfaces and wider gaps between pieces, need steeper pitch to move water off the roof before it penetrates between courses. The thicker butt end of a shake also creates more shadow line and greater gap potential at lower slopes.

Weather exposure (the visible portion of each shingle or shake) varies with slope and product size. The IRC specifies maximum exposure for each combination. For a 16-inch No. 1 shingle on a roof steeper than 4:12, the maximum exposure is 5 inches. For a 24-inch No. 1 shake on a roof steeper than 4:12, the maximum exposure is 7.5 inches. Exceeding these exposure limits leaves insufficient overlap between courses to prevent water infiltration.

On slopes between 3:12 and 4:12 (shingles) or between 4:12 and the maximum, the IRC reduces maximum exposure to compensate for the slower water drainage. Your contractor must calculate the correct exposure for each roof plane based on its specific slope and the product being installed. Using a single exposure across a multi-pitch roof violates code unless every plane exceeds the steeper slope threshold.

Fire Ratings: The Code Requirement That Determines Where Wood Roofing Can Go

Fire code is the single biggest factor limiting wood shake and shingle installations in metro Atlanta. IRC Section R902.1 requires all roofing materials in Georgia to achieve a minimum Class C fire rating. Many local jurisdictions and fire districts within the metro area impose stricter requirements: Class B or Class A ratings in designated residential zones.

Untreated cedar shakes and shingles carry no fire rating. Raw cedar burns. The wood industry addressed this through factory-applied fire retardant treatments that penetrate the wood fibers and provide rated fire resistance. These treatments use chemicals (most commonly phosphate-based compounds) that inhibit flame spread and reduce combustibility. Treated cedar can achieve Class A, Class B, or Class C ratings depending on the treatment formula and application method.

Class A represents the highest fire resistance: effective against severe fire test exposure. Class B represents moderate fire resistance: effective against moderate fire test exposure. Class C represents light fire resistance: effective against light fire test exposure. Testing follows ASTM E108, which subjects the roofing material to a burning brand, intermittent flame, and spread of flame tests at the roof's installed slope.

The fire rating applies to the assembled roofing system, not the shake or shingle alone. The underlayment, the deck material, and the shake or shingle must work together as a tested assembly to achieve the rated classification. Installing fire-rated shakes over a non-conforming underlayment can void the system's fire rating.

Fire retardant treatment also affects the wood's warranty period. Untreated cedar lasts 20 to 30 years in Georgia. Fire-retardant-treated cedar carries manufacturer warranties of 25 to 40 years. Some premium treatments include both fire retardant and UV protection that slows the weathering process and maintains the wood's appearance longer.

Your contractor must provide documentation of the fire rating for the specific shake or shingle product being installed. This documentation includes the test report number, the classification (A, B, or C), the listing agency, and the specific assembly configuration tested. The building inspector verifies this documentation during the permit review and may ask to see it at the jobsite during inspection.

The Interlayment Requirement: Why Shakes Need Felt Between Every Course

IRC R905.8 contains a requirement that separates shake installation from every other roofing material: mandatory interlayment between each course of shakes. This interlayment consists of a strip of No. 30 ASTM D226 roofing felt placed over the top portion of each shake course before the next course is applied.

The interlayment strip must be at least 18 inches wide, and the bottom edge of the felt must be positioned above the butt line of the shake in the course below at a distance equal to twice the weather exposure. For a 24-inch shake with a 10-inch exposure, the felt strip sits 20 inches above the butt line of the course below, meaning it starts at the point where the shake from two courses below ends.

Why does this requirement exist? Shakes split along the grain, creating a rough surface with channels, ridges, and gaps between individual pieces. Water driven by wind can penetrate through these channels and reach the underlayment below. The interlayment felt creates a secondary barrier at each course that redirects this water back onto the shake surface below it. Without interlayment, wind-driven rain during Georgia's summer thunderstorms would reach the underlayment and eventually the deck.

Wood shingles under IRC R905.7 do not require interlayment because their sawn surfaces sit flush against each other with minimal gaps. The tighter fit of shingles provides adequate water resistance at the course level without a secondary felt barrier.

The interlayment requirement adds material cost and labor time to every shake installation. Each course requires a separate felt application. A typical 3,000 square foot roof with 10-inch exposure has approximately 360 linear courses (assuming an average rafter length of 20 feet), and each course needs an 18-inch strip of No. 30 felt. That adds approximately 500 square feet of felt material and 8 to 12 hours of additional labor to the project.

Preservative Treatment: Protecting Wood Roofing in Georgia's Climate

Georgia's climate presents specific challenges for wood roofing. Summer temperatures above 90 degrees with 80% humidity create ideal conditions for mold, mildew, and fungal decay. Annual rainfall of 50 inches keeps wood surfaces wet for extended periods. And the state's mild winters provide minimal freeze protection against insect activity, meaning carpenter ants, termites, and wood-boring beetles remain active 10 months per year.

The IRC does not mandate preservative treatment for wood shakes and shingles when the species is cedar (which contains natural preservative oils). However, the code references AWPA (American Wood Protection Association) standards for treated wood products. AWPA U1 Use Category UC3B covers wood components exposed to weather above ground, which includes roof shakes and shingles.

Factory-applied preservative treatments fall into two categories: oil-borne treatments and water-borne treatments. Oil-borne treatments (using copper naphthenate or other organic biocides) penetrate the wood grain and create a barrier against fungal decay, mold, and insect damage. Water-borne treatments (using copper-based compounds like ACQ or CA-C) provide similar protection but can change the wood's color during the initial weathering period.

For maximum longevity in Georgia, specify factory-treated cedar shakes or shingles with both fire retardant and preservative treatment. Dual-treated products receive fire retardant chemicals first, followed by a compatible preservative treatment. The two treatments work together to resist both fire and biological decay. Single-treated products address one threat and leave the wood vulnerable to the other.

ASTM D3462 covers fire-retardant-treated wood shingles. ASTM D227 covers asphalt-saturated organic felt used as interlayment. These standards work together: a fire-rated wood shake system uses D3462-compliant shakes with D227-compliant interlayment to achieve the rated assembly classification.

HOA Restrictions on Wood Roofing in Metro Atlanta

Building code compliance is necessary but insufficient for wood shake and shingle installations in metro Atlanta. Most planned communities, subdivisions, and condominium associations in Alpharetta, Johns Creek, Roswell, and Marietta maintain covenants, conditions, and restrictions (CC&Rs) that regulate exterior materials. Many of these CC&Rs prohibit wood roofing entirely, regardless of fire rating or treatment.

The fire liability concern drives most HOA wood roofing bans. A burning ember from a neighbor's chimney, grill, or wildfire event can land on a wood roof and ignite it. Even Class A fire-rated wood resists sustained flame exposure, but the liability and insurance implications worry HOA boards and property management companies. The insurance cost for a community with wood roofs runs higher than for communities with non-combustible roofing.

Maintenance concerns add a second layer of HOA resistance. Wood roofing requires periodic treatment (every 3 to 5 years), gutter cleaning to prevent moisture retention at eaves, and moss or mold removal in shaded areas. Homeowners who neglect this maintenance create aesthetic problems for the entire neighborhood, and HOA enforcement of maintenance standards adds administrative burden.

If your HOA permits wood roofing (or if your property sits outside an HOA), verify the local fire district requirements as well. Some fire districts within metro Atlanta counties have adopted local fire prevention codes that restrict wood roofing in areas with wildland-urban interface designations. These restrictions override the IRC's general permission for fire-rated wood products.

For homeowners who want the wood aesthetic without the fire code and HOA complications, composite shake and shingle products offer an alternative. These engineered products use recycled materials, polymer composites, or fiber cement to replicate wood's appearance. They carry Class A fire ratings, require no preservative treatment, and satisfy most HOA material restrictions. Your contractor can present options that deliver the visual character of wood without the code and HOA complications.

Georgia Permit Process for Wood Shake and Shingle Roofing

Every wood shake or shingle installation in Georgia requires a building permit. The permit application for wood roofing requires additional documentation beyond standard roofing permits: the fire test report and classification certificate, the preservative treatment documentation (if applicable), and the specific product's listing with an approved testing laboratory.

Building inspectors in metro Atlanta counties pay close attention to wood roofing installations because the interlayment requirement (for shakes) and fire rating compliance create additional inspection points. The inspector verifies: deck condition and fastener patterns, underlayment type and installation, interlayment placement between shake courses, fastener material (corrosion-resistant nails per code), weather exposure measurements, drip edge installation, and flashing at all penetrations and transitions.

For reroofing projects, Georgia code typically requires complete tear-off of existing wood roofing before installing new wood shakes or shingles. The code prohibits layering new wood roofing over old wood roofing. This requirement exists because the added weight, trapped moisture, and fire risk of doubled wood roofing exceed code limits.

1 Source Roofing and Restoration handles the complete permit and inspection process for wood roofing projects. We verify HOA compliance, confirm local fire district requirements, prepare all permit documentation including fire rating certificates, and coordinate inspections through project completion. Whether you choose asphalt shingles, metal roofing, or wood, we deliver code-compliant installations across metro Atlanta.

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