The Importance of a 2 Hour Fire Rated Wall in Building Design

A fire rating doesn’t come printed on a sheet of drywall. It belongs to a tested assembly: a specific stud, a specific board, a specific number of layers, fastened and sealed a specific way. Change any one of those on site and the wall is no longer the wall that passed the fire test.

For instance, outlets are generally left unsealed because the building code allows for 0.7% (maximum of 100 square inches for every 100 square feet of wall area) of the total area to be left unsealed, one of the areas where sound leaks the most, per OBC Article 3.1.9.3.

If you exceed this threshold, every single box must be physically wrapped with a putty pad.

Today’s strict fire separation rules aren’t meant to make buildings fireproof. They’re meant to slow the spread of a fire, so people have time to get out and firefighters have a chance to put it out before it gets out of control. Think of the old all-wood plaza buildings you still see along Lawrence Avenue in Toronto, built a century ago. Once a fire started, they could go up in flames in 15 minutes. Or think of a basement rental where a kitchen fire spreads through the rest of the house and kills everyone inside within 20 minutes. Fire separation exists to buy that time.

That is why fire rated drywall installation is where most ratings are won or lost. On commercial projects, a substituted board, a missed fastener pattern or an unsealed gap at the deck can turn a passing wall into a failed inspection, a stop-work order or a costly tear-out.

This guide is for general contractors, architects and building officials who need to get fire separations right the first time. We walk through how rated assemblies actually work, what separates a 1-hour wall from a 2-hour one, when the code calls for Type X versus Type C board, and what an inspector will check before signing off. As a commercial drywall and fire separation contractor in the Greater Toronto Area, we build these assemblies on commercial projects across the region, and we’ll flag where they most often go wrong.

A fire-rated wall isn’t a guess, it’s a system that has actually been set on fire in a laboratory and timed to see how long it holds. In Canada, that testing follows CAN/ULC-S101 and gets published as ULC listings. South of the border, the equivalent is ASTM E119 and UL listings, and the Ontario Building Code (OBC) also lists its own generic rated assemblies in the supplementary standards.

Each listing spells out everything down to the last detail: stud size, gauge and spacing, board type and thickness, number of layers, fastener type and spacing, joint treatment, insulation if there is any. Miss one of those and the wall simply isn’t the assembly that earned the rating.

The OBC calls this a fire separation: a wall or floor built to keep fire from spreading from one space into another for a set amount of time. That time comes from the architect’s code analysis, usually 45 minutes, 1 hour, 1.5 hours or 2 hours, depending on occupancy, building area, height and whether the building is sprinklered. From there, it’s on the drywall contractor to build the listed fire separation assembly that actually delivers that protection.

Rated walls usually appear on the drawings as wall-type tags tied to a listing number. Before pricing or framing, confirm three things:

The most common catch at this stage is a rated wall shown stopping at the ceiling line, or a listing that doesn’t actually match the specified board. Flagging either before framing starts saves a costly correction later.

Inspectors don’t take a rating on trust. On a typical commercial job they look for:

Missing any one of these is enough to fail the inspection. A failed inspection on a rated wall usually means opening finished work.

Building Fire-Rated Assemblies on Your Next Commercial Project?

Inaudible Inc. designs and installs 1-hour and 2-hour fire separations across the Greater Toronto Area, backed by listed assemblies and firestop systems done right the first time. Reach out at info@inaudible.ca or  (416) 466-1476 to discuss your project.

The simplest way to see the difference is layers. Most 1-hour steel stud walls use one layer of 5/8″ fire-rated board on each side. Most 2-hour walls use two. The exact build-up always comes from the listing.

The 1-hour wall is the workhorse of commercial interiors. It is quick to build and familiar to every crew, which is also why it gets careless installation. The common failures are wrong fastener spacing, regular board slipped in where Type X was required, and walls that stop at the ceiling instead of running to the deck.

A 2-hour fire rated wall doubles the board, and each layer has its own rules. Base-layer and face-layer fastening differ, and joints must be offset between layers so there’s no straight path through the wall. Adding a layer “to be safe” without following a listing doesn’t create a 2-hour rating. Only a tested 2-hour design does.

Required ratings come from the code analysis, but on commercial projects the pattern is familiar:

OBC Rule (Continuity): Under OBC 3.1.8.3 / 9.10.9.2, the fire-rated ceiling must be entirely continuous and the wall framing must be done afterward. Just like walls, it requires Type X drywall (typically 5/8″) and strict screw spacing.

On a project with a mix of 1-hour and 2-hour fire separations, the foreman and project manager need to keep a sharp eye on the blueprint and stay on top of quality control throughout. A 1-hour fire separation is straightforward to achieve with a single layer of drywall and mineral insulation; a 2-hour separation is not, and the two should never be assumed interchangeable on site.

Both boards are fire-resistant gypsum, but they behave differently under heat. That difference decides which one a listing calls for.

Type X has glass fibres mixed into its gypsum core. When fire drives the water out of the gypsum, the fibres help the board hold together instead of crumbling. Type X drywall is the standard choice for most commercial fire-rated walls and ceilings, almost always in 5/8″ thickness.

Type C goes further. It has more glass fibre plus additives such as vermiculite, which expands under heat and offsets the shrinkage of the gypsum. The result stays intact longer at high temperatures. That lets some listings reach a rating with fewer layers or thinner assemblies.

The last row matters most. Type C is not automatically an “upgrade” over Type X, and Type X is not a safe substitute for Type C. Board names also vary by manufacturer, and each listing names the boards it was tested with. When a product swap comes up for cost or supply reasons, it needs a listing that covers the new board, confirmed by the architect in writing before it goes on the wall.

On one project, Type X was swapped for Type C abuse-resistant board because of a supply shortage, a reminder that even an upgrade needs a listing that covers the substitution before it goes on the wall. See USG’s comparison of Type X vs Type C wallboard for more on how the two boards differ.

Some rated walls can only be built from one side. Elevator hoistways, stair shafts and mechanical chases have no floor on the shaft side to stand on, so a standard stud wall with board on both faces isn’t practical.

Shaftwall systems solve this. Instead of regular studs, they use special profiles, commonly called CH or CT studs, that hold 1″ gypsum shaftliner panels from the accessible side. The liner panels slot into the studs one after another to form the shaft face. The room side is then finished with layers of Type X or Type C board, as the listing specifies, to reach the 1-hour or 2-hour rating.

Shaftwall brings challenges a standard partition doesn’t:

A perfectly built wall still fails if fire and smoke can get around it. The gaps at the top of the wall, at the floor, and around every pipe, duct and cable are where rated assemblies most often break down.

In Canada, firestop systems for penetrations and joints are tested to CAN/ULC-S115 and published as listed systems, just like the wall itself. A tested system specifies the sealant, the backing material, the gap size and the depth. Generic caulk pushed into a gap is not a firestop system.

Three areas need the most attention:

Many rated walls are also acoustic walls, and that is where trades clash. Standard acoustic sealant stays flexible to block sound but is not fire-rated, while some firestop sealants carry an acoustic rating too. On walls that need both, specify a sealant that is listed for fire and tested for sound, so one product covers both requirements.

Where gaps are packed with mineral wool before sealing, the insulation is part of the tested system. We cover that in detail in our guide to firestop insulation at rated joints.

Inaudible Inc favours dense-packed cellulose insulation for soundproofing, which carries a 2-hour fire rating at 10 inches under CAN/ULC-S703 and performs as an airtight barrier. Because fewer inspectors are familiar with the product, we document its listing up front to avoid delays at inspection.

Avoid a Failed Inspection

Unassigned firestopping and missed listings are the most common reasons rated walls fail inspection. Inaudible Inc. can review your fire separation scope before close-in. Call +1 (416) 466-1476 to talk through your project.

Use this list before rated walls are closed in. Each item is a common reason for a failed inspection.

Before framing

During framing and board

Before close-in

Is Type X drywall a 1-hour wall?

Not by itself. Type X is a fire-resistant board with roughly a half-hour fire rating per sheet, but a rating belongs to the whole assembly. One layer of 5/8″ Type X on each side of correctly spaced studs, fastened to a listed design, typically makes a 1-hour wall. The same board on the wrong framing or fastening pattern may not.

How many layers of drywall make a 2-hour wall?

Most 2-hour steel stud walls use two layers of 5/8″ Type X on each side, with joints offset between layers. Some listings reach 2 hours with Type C board or other build-ups. Always follow the listed design.

Do fire-rated walls have to go to the deck?

In most cases, yes. A fire separation generally has to be continuous to the underside of the floor or roof above. A rated wall that stops at the ceiling grid leaves an open path over the top.

How can I tell if drywall is Type X?

The type is printed on the back of each sheet or on the end tape, with the manufacturer’s product name. Inspectors check these stamps, so keep labelled sheets visible until the wall is inspected.

Who is responsible for firestopping?

It depends on the contract. On some projects the drywall contractor handles firestopping; on others each trade seals its own penetrations, or a dedicated firestop subcontractor does it all. Settle this in the scope before work starts. Unassigned firestopping is one of the most common reasons rated walls fail inspection.

Does fire-rated drywall also soundproof a wall?

It helps, because 5/8″ Type X is heavier than standard board, and mass reduces sound transmission. But a rated wall is not automatically an acoustic wall. Sound control also depends on decoupling, cavity insulation and sealing.

Send Inaudible Inc. your architectural drawings and we’ll verify every rated wall type against its listing, catch mismatches before they reach site, and return an itemized takeoff within 24 to 48 business hours.

Or call us at +1 (416) 466-1476, or email info@inaudible.ca to get started.