Fire-Rated Plywood: Treatment, Standards & Performance Ratings

Fire-rated plywood shows up on plans because codes want controlled flame spread, not because wood can ever be fireproof. Fire-rated plywood is wood treated to slow flames and smoke, tested under standards like ASTM E84 to meet building code limits. That rating tells inspectors how the panel acts in a real fire.

Chemical treatment changes how plywood chars under heat. The FR and FRT labels matter, and test results connect directly to code use.

You’ll see where fire-rated plywood fits, how to spot it, and when another material might make more sense.

What Is Fire-Rated Plywood (FR / FRT Plywood)?

Fire-rated plywood, sometimes called FR or FRT plywood, is plywood treated to reduce flame spread and smoke development during a fire. Manufacturers apply fire-retardant chemicals to the wood, usually through pressure treatment.

These chemicals soak deep into the wood fibers, so the surface and core react differently to heat than untreated plywood. Fire-rated plywood is not fireproof.

It doesn’t stop a fire or prevent damage. Instead, it slows how fast flames move across the surface, giving people more time for evacuation and emergency response.

The treatment changes how the plywood behaves under high heat. When exposed to fire, FR plywood forms a char layer on the surface, which limits oxygen and slows the flame.

This layer also reduces smoke. In practice, this helps meet fire safety goals without adding things like sprinklers.

Fire-rated plywood gets tested under ASTM E84, which measures flame spread and smoke index. Many building codes require a Class A flame spread rating—that means low surface flame spread compared to regular plywood.

Fire-rated plywood can be structural or non-structural, depending on its label and treatment. Always check labels and certifications to confirm where you can use it.

Building codes, not appearance, decide when FR or FRT plywood is allowed.

What Does FR / FRT Mean in Plywood?

FR stands for fire-rated, and FRT means fire-retardant-treated. These terms often show up together, but they aren’t identical.

Fire-rated (FR) plywood refers to how a wall, roof, or floor assembly performs in a fire test. The rating comes from a full system test, not just the plywood alone.

In practice, this means the assembly can resist fire for a set time—like 30 or 60 minutes—when built exactly as tested. Fire-retardant-treated (FRT) plywood is plywood that gets fire-retardant chemicals forced in under pressure.

This treatment makes the plywood burn more slowly and produce less flame spread. The material adds less fuel to a fire during early stages.

FRT plywood helps meet code rules, but it doesn’t replace gypsum board in rated assemblies.

Fire-Rated vs. Fire-Retardant vs. Fire-Resistant vs. Fireproof

People use these terms like they’re interchangeable, but they’re not. Each describes a different way materials behave in a fire, based on testing and standards.

Fire-rated is about an assembly, not just a material. A fire-rated plywood wall might carry a 1-hour or 2-hour rating under ASTM E84 or UL tests because the full system resists fire for a set time.

Inspectors look at how the plywood works with studs, fasteners, and finishes—not just the panel. Fire-retardant plywood uses chemical treatment defined by ASTM E84 to reduce flame spread and smoke growth.

The treatment slows surface ignition, so flames spread more slowly. This gives more time before fire grows, but the wood still chars and loses strength if it gets hot enough.

Fire-resistant describes materials that naturally resist fire due to density, mineral content, or structure—think gypsum or concrete. With plywood, fire resistance only applies when testing proves limited heat transfer or structural loss.

Fireproof isn’t a technical term in building codes. No plywood is fireproof. All wood products break down under enough heat.

How Fire-Retardant Treated (FRT) Plywood Is Made

Fire-retardant-treated wood uses a controlled process to change how plywood reacts to heat. The treatment focuses on flame spread, smoke growth, and surface behavior during a fire.

Manufacturers start with standard plywood or treated lumber and place it in a sealed pressure vessel. They inject a water-based fire-retardant treatment under pressure, forcing chemicals deep into the wood fibers.

Because the chemicals bond inside the panel, the plywood meets code rules for fire-retardant-treated wood (FRTW). After impregnation, the panels go through kiln drying—often KDAT (kiln-dried after treatment)—to bring moisture back to a stable level.

The treated plywood installs closer to normal framing moisture and reduces movement on site. When exposed to heat, the chemicals trigger a char layer on the surface, which limits oxygen and slows flame spread.

This delay helps fire-rated assemblies meet ASTM E84 flame-spread limits and smoke ratings required by code.

Does Fire-Retardant Treatment Affect Strength or Durability?

Fire-retardant treatment can change mechanical properties, depending on the chemistry and exposure conditions. Some FRT plywood loses bending strength after long-term heat and moisture exposure.

Roof sheathing and structural uses must follow listed limits. Fastener holding can change too—treated plywood may get more brittle, so builders often adjust nail spacing or use approved fasteners.

Durability depends on location. Most FRTW is rated for dry interior use, not for repeated wetting.

Always check the label and evaluation report. These documents state approved spans, load limits, and whether the treated plywood suits structural or non-structural use.

Fire Ratings and Standards for Plywood

Fire ratings for plywood come from controlled lab tests. These tests measure flame spread 그리고 smoke development under set conditions, so you can compare products using the same scale.

What Is a Class A Fire Rating?

A Class A rating comes from ASTM E84, also known as UL 723. This test measures how fast flame moves across a panel and how much smoke it creates.

Results use two numbers:

• Flame Spread Index (FSI): 0–25 for Class A
• Smoke Developed Index (SDI): 0–450

Untreated red oak sets the baseline at 100 for flame spread. Treated plywood gets a lower number because fire-retardant chemicals change how the wood reacts to heat.

These chemicals promote char instead of open flame. In practice, fire travels more slowly across the surface, and smoke builds at a limited rate.

Class A does not mean non-combustible. It just means the plywood meets the strictest surface-burning limits allowed for wood products in most codes.

What Does “1-Hour / 2-Hour Fire-Rated” Really Mean?

A 1-hour or 2-hour fire rating doesn’t apply to plywood by itself. It applies to a tested assembly, like a wall or ceiling system.

That assembly might include fire-retardant plywood, gypsum board layers, and specific stud spacing, fasteners, and joint details. The rating comes from full-scale fire tests that measure how long the system resists flame, heat, and structural failure.

You can’t swap materials without risk. Changing plywood type, thickness, or fasteners can void the fire rating.

Fire-rated plywood can support a rated assembly, but it never creates the rating on its own.

When Is Fire-Rated Plywood Required by Building Codes?

Building codes require fire-rated plywood when wood surfaces must slow flame spread to protect life and property. You usually see this in the International Building Code (IBC) 그리고 International Residential Code (IRC), both published by the International Code Council (ICC).

Local building codes often adopt these rules with changes, so check local amendments for building code compliance. Fire-rated plywood is required in exterior walls that sit close to a property line.

The IBC and IRC often require a one-hour fire-resistance rating when the wall is less than 5 feet from the lot line. Fire-retardant-treated plywood fits this need because its chemical treatment limits flame spread and smoke.

Roof assemblies can also trigger code requirements. When a fire wall stops at the roof deck, codes often require fire-rated plywood for 4 feet on each side of the wall.

This reduces the chance of fire crossing the wall through the attic. Multi-family buildings add more cases—fire-rated plywood may be needed in walls or floors between units to meet a one-hour separation rating.

What Plywood Can Be Fire-Rated? (CDX, Sheathing, and More)

Fire-rated plywood isn’t a separate wood species. It’s standard plywood that gains an added performance trait through fire-retardant treatment.

This treatment applies to many common plywood products if they meet code and testing rules. CDX plywood often causes confusion—CDX refers to face grades and an exterior glue bond, not fire resistance.

When manufacturers pressure-treat CDX with fire-retardant chemicals, it can meet ASTM E84 flame spread limits. CDX can serve in rated assemblies where codes allow treated wood.

Structural sheathing panels also qualify for fire rating. These panels use multiple plies bonded with heat-resistant adhesives. The treatment penetrates through the plies, so the chemicals help form a char layer when exposed to heat.

This means the panel keeps its shape longer during a fire. Common plywood types that can be fire-rated include:

• CDX and rated sheathing
• Sandeply and underlayment
• Structural panels used in walls, floors, and roofs

Not every plywood panel can be treated for every use. Some fire-retardant treatments limit exposure to moisture or exterior weather.

Match the plywood grade, plies, and treatment listing to the exact wall or floor assembly you plan to build. Always check the panel stamp and treatment label—these markings show the tested standard and approved use, so you know where the plywood can legally and safely go.

Is CDX Plywood Fire-Rated?

No. Standard CDX plywood is not fire-rated. It’s a combustible wood panel, so it’ll catch fire and burn when exposed to flames. The “X” in CDX just means the panel uses exterior-grade glue—it doesn’t mean fire resistance at all.

CDX stands for C-D veneer grades with exterior adhesive. The veneer grades describe the surface quality, and the adhesive resists moisture. But since the panel still uses untreated wood veneers, it burns like any other plywood. CDX alone doesn’t meet fire-rating rules in building codes.

Fire ratings come from ASTM E84 testing, which measures flame spread and smoke. Untreated CDX doesn’t qualify for Class A, B, or C fire ratings under this test. You really can’t count on CDX to slow a fire down.

If you need a fire rating, use Fire-Retardant-Treated (FRT) CDX plywood. Manufacturers pressure-treat these panels with chemical salts that change how wood reacts to heat. The chemicals get forced deep into the fibers, so instead of igniting quickly, the panel chars. FRT CDX can meet Class A flame spread limits when it’s labeled and certified.

Common Uses of Fire-Rated Plywood

Fire-rated plywood goes where codes require slower flame spread and less smoke. Builders use it in walls, ceilings, and other structural components that make up fire-rated assemblies.

These uses support passive fire protection by limiting fire growth without any power or moving parts.

Common placements include:

• Wall and ceiling sheathing in corridors and exits to meet flame-spread limits.
• Public buildings like schools and offices where occupancy loads raise code demands.
• Mechanical rooms where heat sources increase ignition risk.
• Partitions that need to keep ratings when combined with gypsum or insulation.

Treatments change how wood reacts to heat. The panels char at the surface instead of igniting fast. This slows flame spread measured by ASTM E84 ratings like Class A.

Fire-Rated Plywood for Electrical Panels and Backboards

Fire-rated plywood is often required behind electrical panels and control boards. Codes allow wood backboards if they meet a tested flame-spread class, usually Class A under ASTM E84.

The treatment penetrates the panel fibers, so the surface chars and limits flame travel if a fault sparks. Inspectors look for labels that show the rating and the treatment type, not just a surface coating.

Fire-rated plywood holds fasteners well. You can mount breakers, conduits, and data gear without having to add steel backing.

Use it inside fire-rated assemblies when plans call for wood backers. Keep clearances as specified, and avoid field cutting that might remove labels. This keeps the assembly compliant and supports passive fire protection where electrical loads concentrate heat.

Fire-Rated Plywood vs. Regular Plywood

Fire-rated plywood and regular plywood differ in treatment, code use, and fire behavior. The choice depends on safety needs, not just appearance or strength.

Fire-rated plywood gets a chemical treatment under pressure. The chemicals bond with the wood fibers and slow surface flame spread when exposed to heat.

This gives you more time during a fire for evacuation and response. Regular plywood doesn’t get this treatment. Untreated wood ignites and burns at its natural rate, so it doesn’t meet fire code limits for flame spread.

Building codes drive a lot of these decisions. Fire-rated plywood often meets Class A, B, or C flame spread ratings under ASTM E84 or similar tests. Inspectors may require it in corridors, ceilings, or public spaces.

Regular plywood usually fails those requirements. Fire-rated plywood costs more because of the treatment process and testing. The extra cost supports code approval and safer use in regulated areas.

Fire-Rated Plywood vs. Type X Drywall

Fire-rated plywood and Type X drywall serve different roles. They’re not direct substitutes for each other.

Type X drywall contributes to a fire-resistance rating at the wall system level. Fire-rated plywood improves surface flame spread performance of the material itself.

Type X drywall uses a gypsum core with chemically bound water and glass fibers. When exposed to heat, the water releases as steam and slows temperature rise.

This allows tested wall assemblies to reach ratings like 1 hour when installed as listed. Inspectors look at the full assembly, not just the panel.

Fire-rated plywood, also called fire-retardant-treated (FRT) plywood, gets pressure treatment with fire-retardant chemicals. This reduces flame spread and smoke development, often tested under ASTM E84.

The surface burns more slowly, but the panel will still char through its thickness under sustained heat. Building codes and UL listings don’t allow FRT plywood to replace gypsum in rated assemblies. You can add plywood to some listed walls for strength, but only when the listing allows it.

Is Fire-Rated Plywood Waterproof or Suitable for Exterior Use?

Fire-rated plywood is not automatically waterproof or exterior‑ready. Fire resistance, moisture resistance, and weather exposure all need different treatments. Always check the product label to see which ratings it has.

Most fire-rated plywood uses fire‑retardant treatment (FRT) that adds chemicals into the wood fibers. These chemicals slow flame spread by promoting surface charring instead of active burning.

This helps limit fire growth but doesn’t block water. Standard interior FRT plywood can absorb moisture. If exposed to rain or high humidity, the chemicals can leach out, and the panel can lose its fire rating and get weaker if used outdoors.

Exterior fire-rated plywood solves this by meeting ASTM D2898 rain test requirements. This test checks that the treatment stays effective after repeated wetting and drying.

Always verify the FSI/SDI stamp and exterior rating before installing fire-rated panels outside.

How to Identify Fire-Rated Plywood (Stamps & Documentation)

Check the stamp on the panel and match it to formal documents to confirm fire-rated plywood. Codes demand clear labels because surface coatings alone don’t count as fire-rated treatment.

What to Look for on a Fire-Rated Plywood Stamp

Look for a permanent stamp on the edge or back of the panel. If the stamp’s missing, there’s no way to verify the rating.

Key things to check:

• Certification agency like UL (Underwriters Laboratories).
  A UL mark means a third-party inspection tested the plywood to a specific fire standard. That gives you confidence the rating isn’t just a manufacturer’s claim.
• Fire-retardant treatment name, often listed as UL FR-S or similar.
  This tells you which chemical system was used. It’s important because it means the treatment gets into the wood, not just on the surface.
• Flame Spread Index (FSI) with a class rating.
  Class A shows an FSI of 0–25. Lower numbers mean flames spread more slowly, which is what codes want.
• Smoke Developed Index.
  Lower values mean less smoke during a fire, so it’s safer for evacuation.
• Treatment method and drying type, like pressure-treated and kiln-dried after treatment (KDAT).
  Proper drying helps the panel keep its rating over time.

Request supporting documentation too, like UL listings or inspection reports, to confirm the stamp matches approved records.

Fire-Rated Plywood Thicknesses and Common Sizes

Fire-rated plywood comes in the same core sizes as standard panels. Codes focus on fire performance, not special dimensions. This makes it easy to swap in fire-rated panels without changing framing or cabinet layouts.

Common thicknesses are 1/2 inch, 5/8 inch, and 3/4 inch. These sizes balance stiffness and weight while meeting flame spread and smoke development limits.

Thinner panels, like 1/2 inch, work well for wall and ceiling applications where loads are low. Thicker options, like 3/4 inch, support cabinetry, platforms, and assemblies that need extra rigidity. The added thickness increases section depth, which helps with stiffness under load and reduces deflection.

Fire-rated plywood usually comes in 4×8 sheets, matching standard handling and installation practices. Crews can cut, lift, and install panels using the same tools and methods, even when fire ratings are required.

Some products limit certain thicknesses to specific ply counts—like 4-ply, 5-ply, or 7-ply constructions—because ply count affects charring behavior and structural stability during fire exposure.

Cost and Availability of Fire-Rated Plywood

Fire-rated plywood costs more than standard plywood. Manufacturers pressure-treat it with fire-retardant chemicals and test it to meet standards like ASTM E84.

This extra processing bumps up both material and handling costs, which shows up in the final price.

Several factors affect what you’ll pay. Thickness, wood species, and fire rating class (A, B, or C) all matter since each changes how deep the treatment goes and what testing is needed.

A thicker Class A panel usually costs more than a thin Class C panel meant for interior walls.

Availability stays pretty broad in most regions. You can find fire-rated plywood at home improvement stores, building supply yards, and specialty lumber distributors.

Most suppliers keep common sizes like 4 ft × 8 ft sheets in stock. Larger or less common sizes often need a special order.

Common sources include:

• Retail chains for small quantities and quick pickup
• Local lumber yards for contractor-grade options
• Wholesale distributors for bulk orders and consistent supply

Lead times can stretch out for structural or non-standard panels. If your project needs certified structural fire-rated plywood, plan ahead.

Can Fire-Rated Plywood Be Painted or Coated?

You can paint or coat fire-rated plywood, but you need to follow the product listing to keep its fire rating valid. Manufacturers treat these panels with fire-retardant chemicals to meet standards like ASTM E84 or UL 723.

If you use the wrong finish, you might block or mess with that treatment. Always check the manufacturer’s approval list before painting.

Stick with latex-based paints and approved primers made for fire-treated wood. These let the treated surface do what it’s supposed to during a fire, which helps slow flame spread.

Avoid lacquer finishes, thick film coatings, and unapproved oil-based systems. These can seal the surface and mess up the chemical treatment.

If you sand or cut the panel, reseal any exposed edges with a listed fire-retardant coating.

For exterior use, make sure the panel passed a rain test like ASTM D2897. That rating means the treatment won’t wash away after some water exposure.

So, light weather exposure won’t strip away the fire-retardant properties when you use approved coatings.

Pros and Cons of Fire-Rated (FRT) Plywood

Fire-rated plywood slows flame spread because manufacturers treat it with fire-retardant chemicals that react under heat to form a char layer. This gives a bit more time for evacuation and fire response compared to untreated plywood.

Many products meet ASTM E84 Class A or B flame spread ratings, which helps with building code requirements in schools, offices, and multi-family buildings.

FRT plywood keeps its wood-based structure, so you can cut, fasten, and install it with regular tools. It looks and handles like standard plywood, so you can use it in walls, ceilings, and partitions without changing your usual construction methods.

The treatment adds cost because it requires pressure impregnation and testing. Some FRT panels also have limits in high-moisture or exterior settings unless they carry an exterior-rated label.

Fire-rated plywood doesn’t create a full fire barrier. It slows surface flame spread, but it can’t replace gypsum board or tested fire-rated assemblies.

Frequently Asked Questions

Is fire-rated plywood fireproof?

No, fire-rated plywood isn’t fireproof.

Manufacturers treat it with fire-retardant chemicals that react to heat. These chemicals reduce flame spread and slow smoke, so you get a little more time during a fire—but it won’t stop burning forever.

Is fire-rated plywood non-combustible?

No, building codes still call fire-rated plywood combustible.

It’s still wood, so it can burn. The treatment lowers flame spread and heat release, but it doesn’t meet the code definition of non-combustible materials like steel or concrete.

Is all plywood fire-rated?

No, standard plywood doesn’t have any fire-resistance treatment.

Only plywood that’s been treated and tested for fire resistance qualifies as fire-rated. Codes require proof—like ASTM E84 flame spread results. Without that, you have to treat the plywood as plain, untreated wood.

How can I tell if plywood is fire-rated?

Check the product stamp, label, or paperwork.

Fire-rated plywood usually lists a fire-retardant treatment and a test standard, like ASTM E84. You’ll also see a flame spread rating, such as Class A.

Look for third-party certification, maybe an ICC-ES evaluation report or a UL listing. This documentation helps confirm the plywood actually meets code requirements—not just marketing talk.