Fire Rated Plywood: What It Is, When It's Required, and How to Order It Pre-Cut

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Fire rated plywood is plywood that has been pressure-treated with a fire retardant so it slows the spread of flame and smoke. On commercial drywall jobs it shows up as backing: the strips and dado-cut blocks behind the board that hold cabinets, grab rails and handrails. This guide is for general contractors and drywall foremen in Canada who keep seeing “fire rated” on the spec and want to know what it means for the backing in their walls. It isn’t a guide to choosing sheathing, roof decks or exterior panels.

I’m Lewis Murton. I handle EZI BACKR™ at High Crest, which means I spend my days talking to GCs and drywall crews about plywood backing and cutting it to their spec in Surrey, BC. Most of what we cut now is fire rated, so here is what I’ve learned about it from the backing side.

In this guide:

  • What is fire rated plywood?

  • Fire rated plywood rating: what the label actually says

  • When is fire rated plywood required?

  • Where fire-rated backing goes in a commercial building

  • Fire rated plywood thickness for backing

  • Is pressure treated plywood fire rated?

  • Can you cut fire rated plywood on site?

  • What happens when standard plywood goes into a rated wall

  • How to order fire-rated backing pre-cut

  • FAQ

What is fire rated plywood?

Fire rated plywood (you’ll also hear fire retardant plywood, fire treated plywood or FRT plywood) starts as regular plywood. After the mill makes the panels, they go to a treating plant where a fire-retardant chemical is forced into the wood under pressure. The panels are then dried again and stamped.

The treatment changes how the surface burns, so flame spreads more slowly and less smoke is produced. The wood can still burn. That buys time, which is the whole point in a building full of people.

Around here, nearly all of it goes through the same route. The wood is harvested and milled in Washington, Oregon and BC, and the panels go down to a treating plant in Washington. As far as I know, that’s where everyone in our area sends theirs. It’s one of the things that surprised me when I started: there isn’t a local plant doing it.

Fire rated plywood rating: what the label actually says

When a GC calls me for fire-rated backing, they almost never ask about ratings. They say “we need fire rated,” and what they mean is D-Blaze, because that’s the spec everyone here understands and uses. It’s what we cut from.

If you do need to check the numbers, they’re in the manufacturer’s technical specifications sheet. For D-Blaze plywood it lists:

  • Underwriters Laboratories FR-S classification

  • Canadian listings to CAN/ULC S102 and CAN/ULC S102.2 (the Canadian surface-burning tests)

  • A flame spread and smoke developed index of 25 or less

  • AWPA Interior Type A (HT), meaning it’s an interior product

Every piece is ink-stamped by the inspection agency with that classification and the treating plant. That stamp is how an inspector, or you, can tell treated plywood from standard plywood once it’s on site. If you need the full D-Blaze spec sheet, ask us and we’ll send it over.

What I won’t do is tell you which rating your wall assembly needs. That comes from the drawings and the specs.

When is fire rated plywood required?

From where I sit, the honest answer is: when the spec says so. Fire-rated backing is specified by the architects and developers, not chosen by the GC or the drywall sub. They spec it to meet the building code for the province, and the drawings and specs are where your crew finds out.

What has changed is how often it’s specified. About 75% of the plywood we sell for EZI BACKR is now fire rated. It’s easily more than half, and it keeps climbing. Some of the guys who have been around longer than me found it peculiar at first. Why is everything fire rated? On one recent job, every piece of wood they ordered from us was fire rated. We thought that was unusual at the time. Now it looks like the norm for commercial and public buildings.

If you’re bidding a commercial job and the spec book is vague, ask the architect before you price the backing. It’s a lot cheaper to ask than to guess.

Where fire-rated backing goes in a commercial building

Fire rated plywood backing installed between steel studs at grab-rail height in a hospital corridor wall before drywall

The jobs where we see fire-rated backing are offices, hospitals, clinics, retirement homes and pretty much any commercial or public space.

On those jobs, if the spec calls for fire rated, it goes in for every backing application:

  • Cabinetry and millwork

  • Grab bars and handrails in washrooms and corridors

  • The rails along the floor in hospitals and retirement homes

  • Anything else being drilled into or hung on a steel stud wall

So when you’re doing the takeoff, don’t split the job into “rated walls” and “everything else” unless the spec tells you to. On most of the jobs we supply, it’s all fire rated.

Fire rated plywood thickness for backing

For backing, the thickness comes from the spec and what’s being hung, not from the fire rating. EZI BACKR’s fire-resistant plywood comes in the same three thicknesses as our standard plywood: 1/2”, 5/8” and 3/4”. The jobs on our project page, like Brentwood Towers and Scotia Place, used 3/4”.

Is pressure treated plywood fire rated?

No. They are two different treatments that happen to use the same pressure process.

  • Pressure treated plywood is treated against moisture, rot and insects. It’s for wet or moisture-prone areas.

  • Fire rated plywood is treated with a fire retardant. It’s for walls where the spec calls for fire-retardant materials, and it’s an interior product. The manufacturer says to keep it dry in transit and storage and not to install it where it’ll get wet or touch the ground.

We cut both, plus standard plywood. Make sure the order matches the spec, because one doesn’t stand in for the other.

Can you cut fire rated plywood on site?

Yes. Cutting fire-rated plywood on site doesn’t affect its rating. The D-Blaze spec sheet says plywood can be cut in any direction without restriction, and no field coating or end coating is needed on cut edges. It cuts like any other plywood.

So the case for buying it pre-cut is the same as for standard backing: your crew is too expensive to spend their day ripping sheets. Cutting backing on site takes about 20 to 30 minutes per sheet, before anyone vacuums up the sawdust or moves the material around. That adds up quickly across a whole tower.

What happens when standard plywood goes into a rated wall

It doesn’t happen often, but it happens. One crew told me about pulling plywood backing out of a wall and reinstalling fire-rated in its place. That usually comes down to the wrong sheets getting grabbed from a pile on site.

I can’t put a number on what that cost them, and I won’t guess. But think about what it involves: opening up the work, removing the backing, getting the right material, cutting it again and reinstalling it. Then there’s how it looks to the GC and the inspector. Nobody wants to be the sub who has to explain that.

Two habits help prevent it:

  • Check the stamp. Treated plywood is stamped; standard plywood isn’t.

  • Keep fire-rated and standard backing apart on site, or better, order it pre-cut and labelled so the right pieces land at the right floor.

How to order fire-rated backing pre-cut

Stack of pre-cut fire rated plywood backing strips on a pallet, ready to install

EZI BACKR is plywood backing cut to your spec before it ships, and fire-resistant plywood is one of our three wood types. You can order it as:

  • Pre-cut strips: 96” long, widths from 3” to 10”. Used mostly for window and door liners.

  • Dado cut: 15 13/16” wide, sized for 16” on-centre steel studs, heights from 6” to 96”. The dado groove lets the piece hook onto the stud. If your studs are at a different spacing, we can cut to any width.

To quote, we need the size, configuration, thickness and quantity. A takeoff, a drawing or a phone call all work. We cut in Surrey and can turn rush orders around in as little as two business days.

If you want the full step-by-step on installing dado-cut pieces, see my guide to wood blocking in metal studs.

FAQ

What is fire rated plywood used for?

In commercial interiors it’s mostly used as backing in steel stud walls, behind cabinets, grab bars, handrails and other fixtures, on jobs where the architect has specified fire-retardant materials.

When is fire rated plywood required?

When your project’s drawings and specs call for it. Architects and developers specify it to meet the building code, and it’s now common across offices, hospitals, clinics and other public buildings.

How can you tell if plywood is fire rated?

Look for the stamp. Each piece of fire-retardant-treated plywood carries an ink stamp from the inspection agency showing its classification and the treating plant.

Is fire rated plywood the same as fire retardant plywood?

On site, people use the terms interchangeably. Both mean plywood pressure-treated with a fire retardant.

Does cutting fire rated plywood affect the rating?

No. For D-Blaze plywood, the manufacturer allows cutting in any direction without restriction, and cut edges don’t need to be coated.

What thickness of fire rated plywood is used for backing?

EZI BACKR cuts fire-resistant backing in 1/2”, 5/8” and 3/4”. Use whatever thickness your spec calls for.

Get fire-rated backing cut to your spec

You’re buying fire-rated plywood for the job anyway. The question is whether your crew spends hours turning full sheets into backing, or it shows up ready to install. Tell us the size, configuration and quantity and see your price in the quote calculator. It also shows what cutting it on site would cost you.