Frequently Asked Questions

Firestopping is the process of sealing penetrations and gaps in fire-rated walls or floors to maintain their fire resistance ratings. When pipes, conduits, cables, or ductwork pass through these fire-rated assemblies, they create openings that could allow the rapid spread of fire, smoke, and toxic gases.

Firestopping is critical for several reasons:

• Life Safety: It compartmentalizes a building, slowing the spread of fire and smoke. This provides occupants more time to safely evacuate and allows emergency responders more time to act.
• Property Protection: By limiting fire spread, it minimizes damage to property and reduces potential financial losses.
• Code Compliance: It’s a non-negotiable requirement of building codes (e.g. NBCC, OBC, IBC or NFPA). Non-compliant firestopping can lead to project delays, failed inspections, costly rework, and significant legal liabilities.
• System Integrity: It restores the fire rating of the breached assembly, with a 3rd party tested firestop assembly, ensuring the entire passive fire protection system functions as designed.

Firestop products come in various forms, utilizing different mechanisms to achieve their fire-resistive properties, and each is designed for specific applications and conditions:

• • Sealants/Caulks: These are compounds applied into annular spaces around penetrating items or into linear gaps. They form a robust seal and can operate through several mechanisms:
    • Intumescent: These sealants contain chemicals that expand and char when exposed to heat, creating an insulating barrier that seals the opening. They are often crucial for combustible penetrants (e.g., plastic pipes) as they can expand to fill the void left by melting materials.
    • Elastomeric/Non-Intumescent: These sealants form a flexible, durable seal that resists the passage of fire, smoke, and hot gases primarily through their inherent fire resistance and integrity, without significant expansion. They are often used for non-combustible penetrants (e.g., metal pipes) or in dynamic joints where movement is expected.
    • Endothermic: These sealants absorb heat and release chemically bound water vapor, which helps cool the fire-exposed surface and prevent heat transfer.
    • They come in sausages or cartridges for caulk guns or in pails for larger applications.
  • Mortars: Heavier, cementitious compounds mixed with water and poured or troweled into larger openings or for structural applications. They cure to a hard, rigid seal, primarily acting as a physical barrier that resists heat and flame passage. They provide both fire and smoke resistance.
  • Wraps/Collars/Bags:
    • Wraps/Strips: Flexible, intumescent materials wrapped around combustible pipes (e.g., PVC, CPVC, ABS) where they pass through fire-rated assemblies. When heated, they char and expand inward to crush and seal the melting pipe.
    • Collars: Pre-formed intumescent devices that clamp around combustible pipes on one or both sides of the assembly. They function similarly to wraps but offer a quicker, pre-engineered solution.
    • Bags/Pillows: Intumescent bags filled with granular material or mineral wool coated with intumescent material, typically used for temporary seals or in large openings with frequent changes (e.g., cable trays). They expand to fill the void when exposed to heat.

• Blocks/Bricks: Intumescent pre-formed blocks or bricks of intumescent material that are built up like a wall around penetrants in a large opening, similar functionality to bags/pillows but with a different form factor. 

• Putties: Non-curing, pliable compounds that are easy to mold and apply around electrical boxes, cables, or small openings. They often intumesce to seal gaps.
• Boards/Devices (Ablative or Intumescent): Pre-fabricated panels or rigid devices designed for specific applications like large opening seals or for through-penetrations in electrical and data rooms.
  • Ablative: These materials absorb heat at a controlled rate and erode (ablate) in a predictable way, forming a char that protects the substrate beneath and restricts fire spread.
  • Some boards may also incorporate intumescent properties.

A “listed” or “UL/ULC Classified” firestop system means that it has been rigorously tested by a recognized independent third-party testing agency (like Underwriters Laboratories – UL, ULC (Underwriters Laboratory of Canada), Intertek/ETL, or FM Approvals) to meet specific fire resistance standards (e.g., CAN/ULC S115, ASTM E2307, ASTM E814/UL 1479 for through-penetrations, ASTM E1966/UL 2079 for linear joints).

This classification is absolutely non-negotiable because:

• Code Compliance: Building codes mandate the use of listed systems. Using unlisted products or unapproved assemblies is a direct code violation.
• Predictable Performance: Listing ensures the system will perform as expected in a fire scenario, providing the specified F-rating (fire resistance) and T-rating (temperature transmission through the penetration).
• Legal Liability: Contractors are legally responsible for installing firestop systems according to their listings. Deviations can result in severe liability in the event of a fire.
• Insurance Requirements: Code-compliant listed firestop installations are required by most insurance companies.
• Quality Assurance: It provides confidence that the product and assembly meet stringent quality and safety standards.

A listed system specifies all components, including the firestop material, the penetrating item, the construction of the fire-rated barrier, and the exact dimensions (annular space, joint width, material thickness). No deviations are allowed.

F-ratings and T-ratings are crucial metrics assigned to listed firestop systems:

• F-Rating (Fire Rating): This measures the duration for which the firestop system prevents the passage of flame and hot gases through a penetration or joint. It indicates the integrity of the seal and its ability to resist direct fire exposure. An F-rating of 2 hours means the system prevented flame passage for at least 2 hours.
• T-Rating (Temperature Rating): This measures the duration for which the firestop system prevents the passage of heat through a penetration or joint. Specifically, it limits the temperature rise on the non-fire side of the assembly to no more than 325°F (180°C) above ambient. A low T-rating is critical to prevent spontaneous combustion of combustible materials on the non-fire side (e.g., wood studs, insulation, cable insulation). The most prominent requirement for a combined F and T Rating (FT Rating) is found in head-of-wall joints. These joints, which occur at the interface between a fire-rated wall and a fire-rated floor or roof assembly, are required by both the NBCC and OBC to be protected by a firestop system that has been tested and listed with both F and T ratings, ensuring not only flame containment but also the limitation of heat transfer.
• In addition to head-of-wall joints, the two other most common scenarios where FT Ratings are explicitly required include:
• Penetrations through firewalls, as defined under Article 3.1.10.1. of the NBCC and OBC — freestanding, structurally independent fire separations used to divide a building into two or more fire compartments. These walls must maintain their fire-resistance rating independently, and any service penetrations must be protected by a system tested to resist both flame and heat transmission.
• Penetrations through the main structural floor slab separating underground parking from the occupied portion of the building above. These penetrations are subject to strict provisions under Part 3 of the Code, particularly where they involve mixed-use occupancies or a change in major occupancy classification between storeys. Firestop systems in these scenarios must provide both F and T Ratings to maintain compartmentation and prevent the rapid transmission of heat into occupied levels.

Why both are important:

• An F-rating prevents the fire from directly spreading.
• A T-rating prevents the fire from igniting materials on the other side due to heat transfer.
• Codes often require both F and T ratings to match the fire-resistance rating of the assembly being penetrated. For example, a 2-hour fire-rated wall often requires a firestop system with both a 2-hour F-rating and a 2-hour T-rating. T-ratings are critical for penetrations involving combustible items (plastic pipes, electrical cables) or when a fire-sensitive area is on the non-fire side. Non-combustible pipes are equally critical as they are often metal, which is an excellent conductor, and can transfer heat from one room to another quite easily, which can cause combustible material on the other side of the partition to ignite spontaneously.

Even experienced contractors can make costly firestop mistakes. Common pitfalls include:

• Deviating from Listed Systems: This is the most critical mistake. Using a different product, a different penetrating item, an incorrect annular space, or an unapproved wall/floor construction voids the listing. There’s no “close enough” in firestopping.
• Improper Surface Preparation: Failure to clean, prime, or prepare the substrate as per the listing can lead to adhesive failure.
• Incorrect Material Quantity: Using too little material (e.g., insufficient depth of sealant, too few wraps) will compromise the fire rating.
• Damaged or Improper Backer Materials: Using an incorrect type of backer material (e.g., wrong density mineral wool), or damaging it during installation, can affect the system’s performance.
• Inadequate Support for Penetrations: Heavy pipes or conduits not properly supported can stress the firestop seal and lead to cracks or gaps.
• Applying Firestop to Unrated Assemblies: Firestop systems are designed for rated assemblies. Applying them to non-rated walls doesn’t magically make the wall fire-rated.
• Lack of Documentation: Failing to properly document installations (photos, signed inspection tags, completion certificates) can lead to problems during inspections or in post-construction audits.
• Ignoring Dynamic Movement: For expansion joints or areas with significant movement, using a rigid firestop material instead of a flexible one designed for movement will lead to premature failure.

Rigorous documentation and quality control are paramount for firestopping:

• Pre-Installation Planning:
  • Review Drawings & Specifications: Identify all fire-rated assemblies and required firestop locations.
  • Access Manufacturer Data: Obtain and review the specific UL/ULC/ETL/FM listing numbers, installation instructions, and Material Safety Data Sheets (MSDS/SDS) for all specified firestop products.
  • Verify Approved Methods: Ensure the penetrations match the exact conditions of a listed system (e.g., pipe material, size, annular space, assembly type).
• During Installation:
  • Dedicated, Trained Installers: Use personnel specifically trained and, ideally, certified in firestop installation.
  • Strict Adherence to Listings: Install every firestop system precisely as per its UL/ULC/ETL/FM design details.
  • Photo Documentation: Take clear, timestamped photos of installations before they’re covered up, showing the product, penetration, and surrounding assembly.
  • Firestop Tags: Apply permanent, legible firestop tags to each firestopped penetration, indicating the design number, date, and installer.
• Post-Installation & Inspection:
  • Third-Party Inspections: Engage third-party special inspectors (mandated in many jurisdictions) to verify compliance. While firestop manufacturers rigorously test and publish detailed solutions, it is important to recognize that they are also product suppliers with a commercial interest in the outcome of a project. As such, they do not qualify as independent third parties under building code requirements or industry best practices. To ensure objectivity, protect against liability, and maintain code compliance, inspections should always be conducted by a qualified and certified third-party agency that has no financial stake in the materials used or the outcome of the installation.
  • Completion Certificates: Provide detailed documentation for the building owner and authorities having jurisdiction (AHJ), including product data sheets, listed design numbers, and installation logs.
  • Punch List & Remediation: Promptly address any deficiencies identified during inspections.

Proper documentation proves that work was done correctly, protecting the contractor and the building owner, and is essential for gaining occupancy permits.

Backer rod serves several essential functions, making it indispensable for proper sealant installation and long-term joint performance:

• Controls Sealant Depth: It ensures the sealant is applied at the optimal width-to-depth ratio (typically 2:1 for most high-performance sealants like silicones and polyurethanes). This allows the sealant to stretch and compress effectively across the joint, preventing it from being too thick (which limits movement) or too thin (which leads to premature failure).
• Prevents Three-Sided Adhesion: By preventing the sealant from bonding to the back of the joint, the backer rod allows the sealant to flex freely as the joint expands and contracts. Adhesion on three sides severely restricts movement capability and leads to cohesive failure (splitting) or adhesive failure (detachment) of the sealant.
• Provides a Firm Tooling Surface: It offers a uniform, non-adhering surface against which the sealant can be tooled, ensuring a consistent and aesthetically pleasing bead profile.
• Conserves Sealant Material: By filling the void behind the sealant, it reduces the amount of expensive sealant required, leading to cost savings on large projects.
• Aids in Proper Curing: For moisture-curing sealants (like most silicones and polyurethanes), certain backer rod types can allow moisture vapour to reach the back of the sealant, facilitating a complete and uniform cure.

The primary types of backer rods are distinguished by their cell structure and composition, and understanding these differences is crucial for optimal sealant performance and avoiding common failures:

• 1. Closed-Cell Backer Rod:
  • Composition: Made of non-absorbent foam (e.g., polyethylene or polyolefin) with discrete, sealed cells of gas (typically air or nitrogen).
  • Properties: Inherently non-absorbent to water and moisture, provides a firm support, and in its intact state, is considered non-gassing. This means it won’t continuously release internal gases into the curing sealant.
  • Critical Nuance for Outgassing: It’s vital to understand that if a closed-cell backer rod is punctured, torn, or severely over-compressed during installation, these sealed gas cells can rupture. When this happens, the trapped gas can escape into the wet sealant, potentially causing bubbling or blistering as the sealant cures. This is why careful installation with blunt tools is paramount.
  • Ideal Applications:
    • Exterior joints or wet areas: Where preventing moisture intrusion from the back of the joint is crucial (e.g., window perimeters, shower stalls).
    • Vertical or overhead joints: Its firmer consistency provides excellent support for the sealant bead and prevents sag.
    • When minimizing outgassing from the backer rod itself is critical: Especially important for sealants like silicones and some polyurethanes that are sensitive to gas release, provided the backer rod remains uncompromised.
• 2. Hybrid Backer Rod (Open-Cell Core with Closed-Cell Skin):
  • Composition: Features a soft, open-cell foam core encased in a durable, closed-cell polyethylene skin.
  • Properties: Offers a unique combination of benefits. The closed-cell skin provides a non-absorbent, non-gassing surface directly to the sealant, preventing water absorption into the rod’s core and eliminating the risk of bubbling from gas release from the rod’s core itself. The open-cell core maintains the rod’s flexibility and compressibility, making it easy to install and conform to irregular joints.
  • Clarifications:
    • Vapour Transmission: While the closed-cell skin directly facing the sealant acts as a vapour barrier at that interface, the open-cell core remains permeable. This means the hybrid rod does not create a complete vapour block behind the skin, allowing some moisture vapour from the underlying substrate to move within the joint assembly, which can be beneficial for the cure of moisture-sensitive sealants by creating a more balanced moisture environment. However, direct vapour transmission through the skin to the sealant is limited.
    • Cost: Hybrid backer rods are generally considered a premium product due to their dual material composition and manufacturing complexity. Their cost typically falls above standard closed-cell polyethylene rods, reflecting their advanced properties. 
  • Ideal Applications:
    • Versatile use: Suitable for a wide range of applications where a balance of excellent weather resistance (from the skin) and good workability (from the soft, compressible core) is desired.
    • Demanding building envelope joints: Where the sealant needs a clean, stable, non-gassing surface to bond to, but the backer rod also needs to accommodate significant joint movement without putting undue stress on the sealant.
• 3. Open-Cell Backer Rod:
  • Composition: Made of absorbent foam (e.g., polyurethane) with an interconnected cell structure.
  • Properties: Absorbent to water, softer, and allows moisture vapour and air to pass through its structure. This “breathability” means it will allow outgassing from the substrate to pass through it, potentially causing bubbles in the sealant if the substrate itself is outgassing.
  • Ideal Applications:
    • Moisture-curing sealants (e.g., some silicones, polyurethanes) in deep or inaccessible joints: Where ambient moisture from the back of the joint is needed to facilitate a complete and uniform cure, as it allows moisture vapour to reach the sealant.
    • Interior joints: Where water absorption is less of a concern and its softer nature can conform well to irregular joint shapes.
    • When a softer, more compressible material is needed: Ideal for irregularly shaped joints or when minimal stress on joint edges during installation is desired.
    • Firestop applications: Some open-cell backer rods are specifically designed as part of fire-rated systems.

Correct sizing is crucial for optimal performance:

• General Rule: The backer rod should be approximately 25% larger than the joint width. For example, for a 1-inch wide joint, use a 1-1/4 inch backer rod.
• Installation Method: It should be installed by compressing it into the joint, creating a tight friction fit without overstretching or puncturing it.
• Consequences of Incorrect Sizing:
  • Too Small: If the backer rod is too small, it won’t create the necessary bond breaker or provide adequate support, leading to improper sealant depth, or sealant sag.
  • Too Large: If it’s too large, it can be difficult to install without tearing or puncturing. Over-compression can create excessive outward pressure, leading to “hourglassing” of the sealant (a narrow waist), which concentrates stress and can cause premature failure. It can also cause the backer rod to “mushroom” out, affecting the sealant’s bond area.

Yes, backer rods can be compromised during installation, which can directly lead to sealant failure and compromise the integrity of the joint system:

• Punctures or Tears (Especially for Closed-Cell): Using sharp tools (like utility knives or screwdrivers) or forcing an oversized backer rod can puncture or tear the skin of a closed-cell backer rod. When the sealed cells are ruptured, the trapped gases (typically air or nitrogen) can escape into the wet, curing sealant. This release of gas is the primary cause of bubbling or blistering in the sealant bead, particularly for sensitive chemistries like silicones. Additionally, a damaged skin can interfere with its non-adhering properties, potentially leading to three-sided adhesion if the sealant bonds to the compromised core.
• Overstretching: Stretching the backer rod excessively during installation can reduce its effective diameter and density. This prevents it from creating the necessary friction fit, providing proper support, or acting as an effective bond breaker, ultimately compromising the sealant’s movement capability.
• Contamination: Getting dirt, dust, grease, oils, or incompatible materials on the backer rod can negatively affect the sealant’s adhesion to the joint substrate, or even interfere with the sealant’s cure.

Prevention is key to avoiding these issues:

• Use Proper Tools: Always use blunt-edged, rounded, or specially designed backer rod insertion tools. Your thumb or a blunt putty knife are often effective.
• Avoid Sharp Objects: Never use utility knives, screwdrivers, or other sharp tools to push or prod the backer rod into place.
• Select Correct Size: Ensure the backer rod is sized appropriately (approximately 25% larger than the joint width) to achieve a snug friction fit without excessive force.
• Handle Carefully: Handle backer rods with clean hands or gloves to prevent contamination.
• Proper Storage: Store backer rods in a clean, dry environment, protected from physical damage and extreme temperatures, to maintain their integrity.
• Smooth Installation: Uncoil and cut backer rod neatly, avoiding kinks or twists, to ensure uniform placement within the joint.

Omitting or substituting the backer rod with unsuitable materials significantly compromises the sealant joint:

• Three-Sided Adhesion: This is the most common and detrimental consequence. The sealant bonds to the back of the joint, inhibiting its ability to move freely and leading to premature splitting or detachment.
• Improper Sealant Depth: Without a backer rod, it’s impossible to consistently control the sealant depth, resulting in either too much material (reduced movement, higher cost) or too little (insufficient strength).
• Increased Sealant Consumption: More sealant is used than necessary, leading to increased material costs and potentially longer cure times.
• Poor Aesthetics: An uneven or inconsistent bead profile due to lack of a firm tooling surface.
• Reduced Durability & Lifespan: The joint will fail prematurely, leading to water intrusion, air leakage, and costly callbacks.
• Warranty Voidance: Most sealant manufacturers’ warranties are voided if the sealant is not installed over a compatible backer rod.
• Inappropriate Substitutes: Using materials like sand, gravel, wood, or inconsistent packaging materials as substitutes will not provide the necessary bond-breaking, compressibility, or support, leading to guaranteed failure.

Backer rod is available in diameters typically ranging from 1/4″ to 6″ (6 mm to 150 mm). The rod should be 25% larger than the joint width to ensure it stays in place without adhesive.

Yes. It’s commonly used in both:

• Horizontal: Expansion joints in sidewalks, parking decks, floors. Commonly closed-cell backer rod would be installed in exterior horizontal joints to prevent the possibility of water absorption and subsequent potential freezing, which would compromise the sealant on top.
• Vertical: Curtain walls, precast panels, tilt-up walls, window perimeters.
  Make sure it’s properly seated without stretching or over-compressing.