Fire Rating Requirements for Commercial Buildings in Colorado
Understanding IBC fire-resistance ratings, occupancy classifications, and what they mean for your project's fireproofing specifications.
Every commercial building in Colorado must meet fire-resistance rating requirements established by the International Building Code (IBC). These ratings determine how long structural elements—columns, beams, floor assemblies, and load-bearing walls—must maintain their integrity during a fire. For general contractors, architects, and project managers, understanding these requirements is essential for planning fireproofing scope, writing accurate specifications, and avoiding costly mid-project changes.
This guide breaks down the IBC fire-resistance rating system, explains how construction types and occupancy classifications drive fireproofing requirements, and covers what Colorado-specific amendments you should be aware of. Whether you are bidding a new high-rise in downtown Denver or a school renovation in Colorado Springs, this resource will help you scope the fireproofing work accurately from day one.
What Is a Fire Rating?
A fire rating (or fire-resistance rating) is the measured time, expressed in hours, that a building element can withstand exposure to a standard fire test without structural failure. These ratings are determined through standardized laboratory testing per ASTM E119, the most widely referenced fire test standard in the United States.
During an ASTM E119 test, a full-scale assembly (such as a steel column wrapped in fireproofing material) is exposed to a furnace that follows a prescribed time-temperature curve, reaching over 1,700°F within the first hour. The assembly must maintain structural stability and prevent flame passage for the full rated duration.
Standard Ratings
1-hour, 1.5-hour, 2-hour, 3-hour, and 4-hour. The required rating depends on construction type and building element.
Applies To
Structural frame (columns and beams), bearing walls (exterior and interior), floor assemblies, and roof assemblies.
The fire rating is not a prediction of real-world fire performance—it is a standardized benchmark. A 2-hour rating means the assembly survived a 2-hour ASTM E119 test. In practice, building fires vary enormously in temperature, fuel load, and ventilation. The rating system provides a consistent, code-compliant method for specifying fire protection across different building types.
IBC Table 601 — Fire-Resistance Rating Requirements by Construction Type
Table 601 of the International Building Code is the primary reference for determining fire-resistance ratings. It maps each building element to the required rating (in hours) based on the building's construction type. Here is a simplified version of the table:
| Building Element | Type I-A | Type I-B | Type II-A | Type II-B | Type III-A | Type III-B |
|---|---|---|---|---|---|---|
| Structural frame | 3 hr | 2 hr | 1 hr | 0 hr | 1 hr | 0 hr |
| Bearing walls (exterior) | 3 hr | 3 hr | 2 hr | 2 hr | 2 hr | 2 hr |
| Bearing walls (interior) | 3 hr | 2 hr | 1 hr | 0 hr | 1 hr | 0 hr |
| Floor construction | 2 hr | 2 hr | 1 hr | 0 hr | 1 hr | 0 hr |
| Roof construction | 1.5 hr | 1 hr | 1 hr | 0 hr | 1 hr | 0 hr |
Note: This is a simplified reference. The full IBC Table 601 includes additional construction types (Type IV, Type V) and footnotes that may affect requirements. Always refer to the current edition of the IBC and any local amendments for your jurisdiction.
Common Building Types and Their Typical Ratings
While the specific fire rating is always determined by the project's construction type and occupancy classification, certain building types consistently fall into predictable categories. Knowing these patterns helps GCs estimate fireproofing scope early, even before specifications are finalized.
Hospitals and Healthcare Facilities
Type I-A — 3-hour structural frameThe highest fire-resistance requirements in the IBC. Patients cannot self-evacuate, so the code demands maximum structural protection. Expect the thickest SFRM applications and the most rigorous inspection requirements on these projects.
High-Rise Office Buildings
Type I-B — 2-hour structural frameAny building with an occupied floor more than 75 feet above the lowest level of fire department vehicle access is classified as a high-rise. These projects typically require 2-hour fireproofing on columns and beams, with 2-hour floor assemblies for compartmentation.
Schools and Educational Facilities
Type II-A — 1-hour structural frameSchools are typically constructed as Type II-A, requiring 1-hour fire-resistance ratings on the structural frame. The lower rating reduces fireproofing material thickness but the work still requires UL-listed assemblies and third-party inspection.
Warehouses and Industrial Buildings
Type II-B — Often 0-hour (unrated)Many warehouse and light industrial buildings use Type II-B construction with no fire-resistance requirement on structural elements. However, insurance carriers, tenant requirements, or high-piled storage conditions may still require SFRM or intumescent coatings even when the code does not.
Parking Garages
Varies — Typically 2-hourOpen parking garages often qualify for reduced fire ratings, but enclosed or below-grade garages typically require 2-hour structural frame protection. The specific classification depends on ventilation, the number of tiers, and whether the garage supports occupied floors above.
How Fireproofing Meets These Ratings
Fire-resistance ratings are achieved through tested assemblies—specific combinations of structural members and fire-resistive materials that have passed ASTM E119 testing. Each tested assembly is assigned a UL (Underwriters Laboratories) design number that specifies the exact materials, thicknesses, and application methods required.
For structural steel, the two primary fireproofing methods are spray-applied fire-resistive materials (SFRM) and intumescent coatings. Each method has different thickness requirements for the same fire rating, and the specific UL assembly dictates which method and thickness applies.
Spray-Applied Fireproofing (SFRM)
SFRM thickness directly correlates to the fire rating—thicker application equals a higher rating. A typical SFRM product like BlazeShield II might require 9/16″ for a 1-hour rating on a W10x49 column but 13/16″ for a 2-hour rating on the same member. The exact thickness varies by the steel member's weight-to-heated perimeter ratio (W/D), which is why the UL design number and the specific structural shape both matter. SFRM is the most cost-effective method for concealed structural steel and is used on the vast majority of commercial projects in Colorado.
Intumescent Coatings (IFRM)
Intumescent coatings are thin-film materials that expand when exposed to heat, forming a protective insulating char. The dry film thickness (DFT) required varies by the fire rating and the steel member's section factor. Intumescent coatings are typically specified when the structural steel will be exposed to view—lobbies, atriums, open-plan offices—because they provide a clean, paintable finish. They cost significantly more than SFRM per square foot but eliminate the need for cladding or enclosure to hide the fireproofing.
UL Assembly Numbers
The specified UL assembly number on the project drawings tells the fireproofing contractor exactly what to apply, how thick, and to which members. Common UL assembly designations include X-numbers for columns (e.g., X772) and D-numbers and N-numbers for floor and roof assemblies. If the UL assembly is not clearly specified in the project documents, the fireproofing contractor should request clarification from the architect of record before bidding.
Colorado-Specific Requirements
Colorado adopts the International Building Code as the basis for its statewide building code, but local jurisdictions have the authority to adopt additional amendments. This means fire-resistance requirements can vary depending on where your project is located within the state.
State-Level Adoption
Colorado adopts the IBC through the Colorado Division of Fire Prevention and Control. The current statewide adoption is based on the 2021 IBC. However, Colorado is a home-rule state, meaning municipalities can adopt their own code editions and amendments, provided they meet or exceed the state minimum. Always verify which code edition your jurisdiction has adopted before starting design.
Denver Amendments
The City and County of Denver maintains its own fire code amendments that can be more stringent than the base IBC. Denver's amendments include additional requirements for high-rise buildings, mixed-use occupancies, and fire department access. If your project is in Denver, you must reference the Denver Building and Fire Code rather than relying solely on the state-adopted IBC.
Other Key Jurisdictions
Colorado Springs, Boulder, Aurora, and Fort Collins each maintain their own code adoptions and may include local amendments. For projects outside the Denver metro area, confirm the local code edition and any supplemental fire protection requirements with the building department early in the permitting process. Pikes Peak Regional Building Department (Colorado Springs) and the City of Boulder, in particular, are known for thorough plan review processes.
Special Occupancies
Certain occupancies trigger additional requirements beyond the base construction type. Hospitals and ambulatory care facilities must comply with NFPA 101 (Life Safety Code) in addition to the IBC. High-rise buildings (occupied floors above 75 feet) must meet IBC Section 403, which adds requirements for secondary water supply, emergency voice/alarm communication, and fire command centers. K-12 schools have specific egress and compartmentation requirements under IBC Chapter 10 and applicable state guidelines.
What General Contractors Need to Know
For GCs managing commercial construction projects in Colorado, fire-resistance ratings directly affect your schedule, budget, and subcontractor coordination. Here are the practical takeaways for managing fireproofing scope effectively.
Find the Ratings on Your Drawings
Fire-resistance ratings are documented on the structural drawings (S-series) and in the project specifications. Look for UL assembly numbers called out on column and beam schedules, floor assembly details, and the structural general notes. The specification section for applied fireproofing is typically 07 81 00 (Applied Fireproofing). Firestopping is a separate specification section: 07 84 00 (Firestopping).
Involve Your Fireproofing Sub Early
Getting your fireproofing subcontractor involved during preconstruction helps you catch specification gaps, identify scope conflicts with other trades, and produce a more accurate bid. Fireproofing is often one of the last trades on the schedule but one of the first that needs to be coordinated—steel erection sequence, decking, and MEP rough-in all affect fireproofing access and application order.
Understand the Inspection Process
Third-party inspection of fireproofing thickness and density is required on most commercial projects. The inspector measures SFRM thickness at specific intervals using calibrated gauges and compares readings to the UL assembly requirements. Self-testing every area before calling for third-party inspection is the single most effective way to avoid failed inspections, re-work, and schedule delays.
Separate Fireproofing from Firestopping
Fireproofing (07 81 00) protects structural elements from fire. Firestopping (07 84 00) seals penetrations and joints in fire-rated assemblies—pipe penetrations, electrical conduit, curtain wall perimeters, and expansion joints. These are different scopes, often performed by the same subcontractor but bid and specified separately. Make sure both are accounted for in your buyout.
Plan for Schedule Impact
SFRM application requires the structural steel to be erected, decking installed, and the area reasonably enclosed (SFRM cannot be applied in rain or freezing conditions without protection). Intumescent coatings can sometimes be applied in the shop before erection, which can accelerate the field schedule. Coordinate with your fireproofing sub to determine whether shop or field application makes sense for your project timeline.
Frequently Asked Questions
What determines the fire rating for my building?
The fire rating for your building is determined by three primary factors: construction type (Type I through Type V as defined in IBC Table 601), occupancy classification (such as Assembly, Business, Educational, or Institutional), and building height and area. The architect of record evaluates these factors during design and specifies the required fire-resistance ratings on the structural drawings and in the project specifications.
What is the difference between 1-hour and 3-hour fire ratings?
The number refers to the duration (in hours) that a building element must maintain its structural integrity when exposed to a standard fire test per ASTM E119. A 1-hour rating means the assembly must resist fire for 60 minutes without failure; a 3-hour rating requires 180 minutes. Higher ratings demand thicker fireproofing materials. For example, spray-applied fireproofing on a W-shape steel column might require roughly 9/16 inch for a 1-hour rating but over 1-1/2 inches for a 3-hour rating, depending on the steel section size and UL assembly.
Does every commercial building need fireproofing?
Not every commercial building requires applied fireproofing. Type II-B and Type V-B construction, for instance, have 0-hour fire-resistance requirements for structural elements. However, even buildings with no code-mandated fire rating may still require fireproofing for insurance compliance, tenant improvement requirements, or occupancy-driven fire separation walls. Firestopping at penetrations and joints is almost always required regardless of construction type.
Who determines the fire rating requirements?
Fire rating requirements are established by the building code (IBC), as adopted and amended by the State of Colorado and the local jurisdiction. The architect of record interprets these requirements for the specific project and documents them in the construction drawings and specifications. The local building official (AHJ — Authority Having Jurisdiction) has final authority on code compliance during plan review and inspection.
How does building height affect fire rating requirements?
Building height is one of the primary drivers of construction type and, therefore, fire rating requirements. Buildings over 75 feet in height are classified as high-rises under the IBC and must be Type I-A or I-B construction, which requires 2-hour or 3-hour structural frame ratings. Taller buildings carry greater life safety risk during evacuation, so the code requires more robust fire resistance. Height also triggers additional requirements such as automatic sprinkler systems and standpipe systems.
Can fire ratings change during construction?
Yes. Fire rating requirements can change if there are design revisions that alter the building’s construction type, occupancy classification, or height and area. Value engineering, scope changes, or code interpretation updates from the AHJ can all trigger revised fire-resistance requirements. When changes occur, the fireproofing subcontractor needs updated drawings and specs to adjust material thickness, coverage area, and UL assembly references. Early involvement of your fireproofing contractor helps manage these changes without schedule delays.
Have Questions About Fire Rating Requirements for Your Project?
Our team has applied fireproofing on over 7,500 commercial projects across Colorado since 1988. If you need help understanding the fire-resistance requirements for your next build, we are here to help.