Type I construction is the International Building Code’s most fire-resistant classification, requiring noncombustible structural materials and fire-resistance ratings as high as three hours on the primary structural frame. The IBC divides it into two subcategories, Type IA and Type IB, with IA setting the highest protection standard in the entire code. That fire performance is why nearly every modern high-rise is built as Type I: the classification unlocks unlimited heights and floor areas for most occupancy groups.
Type IA vs. Type IB Fire-Resistance Ratings
IBC Table 601 assigns a fire-resistance rating, measured in hours, to each major building element. The rating is how long the element must withstand a standardized fire before losing structural integrity or letting fire pass through.1International Code Council. 2018 International Building Code – Chapter 6 Types of Construction
- Primary structural frame: 3 hours for Type IA, 2 hours for Type IB.
- Exterior bearing walls: 3 hours for IA, 2 hours for IB.
- Interior bearing walls: 3 hours for IA, 2 hours for IB.
- Floor construction: 2 hours for both.
- Roof construction: 1½ hours for IA, 1 hour for IB.
- Nonbearing interior partitions: no rating required by Table 601, though other code sections may impose one.
The practical difference between the two subcategories is one hour on the frame and bearing walls, plus a half-hour on the roof. Floor construction is identical, so both offer the same protection against fire spreading between stories.
Table 601 footnotes allow some reductions. When a frame member or bearing wall supports only the roof, its required rating drops by one hour. When every part of the roof sits 20 feet or more above the nearest floor below, fire protection of roof framing and decking is not required at all, except in F-1, H, M, and S-1 occupancies. A Type IB warehouse with high ceilings can take advantage of that exemption and leave its steel roof deck unprotected, which materially changes the fireproofing budget.
Noncombustible Materials and What the Code Still Allows
IBC Section 602.2 requires every building element in Table 601 to be made of noncombustible materials. In practice that means the structural frame, bearing walls, floors, and roof assemblies are reinforced concrete, structural steel, or masonry rather than wood.
The code does not call something noncombustible by label alone. A material earns the classification by passing ASTM E136, a furnace test at roughly 1,500°F. To pass, the sample cannot flame visibly beyond the first 30 seconds, cannot raise the furnace temperature by more than 54°F, and cannot lose more than half its mass. All three criteria must be met.2ICC NTA. IBC Building Construction Types for Combustibility
Section 603 then carves out a long list of combustible materials that remain permitted, because finishing a building would otherwise be nearly impossible. Fire-retardant-treated wood is allowed in nonbearing partitions rated at two hours or less, in nonbearing exterior walls where no fire rating is required, and in roof construction. In Type IA buildings taller than two stories, fire-retardant-treated wood in the roof is permitted only if the roof sits at least 20 feet above the floor below. Thermal and acoustical insulation is allowed when its flame spread index is 25 or less, or up to 100 if it’s sandwiched between noncombustible layers. Foam plastic insulation is permitted under Chapter 26, which generally requires a thermal barrier of half-inch gypsum or equivalent between the foam and the interior. Door frames, window sashes, interior wall and ceiling finishes, trim, millwork, and floor coverings are all permitted when installed per their respective code sections. Class A, B, or C roof coverings are allowed regardless of combustibility.3UpCodes. Section 603 Combustible Material in Types I and II Construction
The point is worth absorbing before pricing a project: the noncombustible rule governs the structural skeleton, not every component inside the building.
How Tall and How Large You Can Build
The fire performance of Type I translates directly into the largest allowable building dimensions in the IBC. Type IA buildings get unlimited stories for nearly every occupancy group, which is why the classification is the default for skyscrapers, large hospitals, and major institutional buildings. Type IB allows substantial height but imposes story caps that vary by occupancy.
Under IBC Table 504.4, with sprinklers (required for most Type I high-rises):
- Business, Residential R-1 and R-2, and Mercantile: unlimited stories for IA, 11 stories for IB.
- Assembly A-1 (theaters): unlimited for IA, 5 stories for IB.
- Assembly A-2 (restaurants) and A-3 (worship, recreation): unlimited for IA, 11 stories for IB.
- Institutional I-2 (hospitals): unlimited for IA, 4 stories for IB.
- Educational: unlimited for IA, 5 stories for IB.
- High-hazard H-1: 1 story for both.
Type IA receives unlimited allowable floor area for most occupancy groups as well. Type IB typically receives unlimited floor area for many groups but may have limits for certain institutional and high-hazard occupancies. The practical choice between IA and IB is a choice between unlimited height and a cap that, for most commercial uses, tops out around 11 stories.4International Code Council. 2024 International Building Code – Chapter 5 General Building Heights and Areas
High-Rise Systems Required by Section 403
Most Type I buildings cross the IBC’s high-rise threshold, which triggers a separate layer of life safety requirements under Section 403. These add cost and complexity on top of the basic Type I material and rating rules.
High-rise buildings must be equipped throughout with an automatic sprinkler system complying with NFPA 13. In seismic design categories C through F, that system must have a secondary on-site water supply capable of meeting the full sprinkler demand for at least 30 minutes. Buildings taller than 420 feet face additional requirements: each sprinkler zone must be fed by at least two risers supplying alternate floors, and the fire pumps must connect to at least two separate water mains on different streets.5International Code Council. 2021 International Building Code – Chapter 4 Special Detailed Requirements Based on Occupancy and Use
Section 403 also requires a fire alarm system, a standpipe system throughout the building, and a fire command center in a location approved by the fire code official. The command center is the operational hub for firefighters during an emergency and houses controls for the alarm, sprinkler, elevator recall, and communication systems.
Fireproofing Methods and Costs
Structural steel is strong but loses roughly half its load-carrying capacity around 1,100°F, which a building fire can reach in minutes. Fireproofing buys time by insulating the steel from heat. Three methods dominate Type I construction.
Spray-applied fire-resistive material, or SFRM, is the workhorse of commercial fireproofing. Cementitious or mineral-fiber material is sprayed directly onto beams, columns, and decking. Standard-density SFRM is the cheapest option and works well for concealed members. Medium and high-density formulations cost more but hold up better in areas with foot traffic, vibration, or moisture. Installed costs run roughly $5 to $9 per square foot for standard product, $7 to $12 for medium-density, and $20 or more for high-density formulations used in harsh environments.
Intumescent coatings look like ordinary paint at room temperature but swell into a thick insulating char when heated. They’re used on exposed structural steel where aesthetics matter, such as lobby columns and atrium trusses. Pricing runs from about $6 per square foot for basic water-based products to $35 or more for epoxy systems rated to the UL 1709 hydrocarbon curve. Winter application in cold climates adds another $2 to $5 per square foot for temporary heating and enclosure.
Concrete encasement surrounds steel members in poured or precast concrete. It’s most common on columns and is inherently more durable than coatings because the protection is structural rather than applied. The tradeoff is added dead load and longer construction timelines.
Designers select tested assemblies from directories maintained by UL and other listing agencies rather than engineering ratings from scratch.6UL Solutions. Structural Steel Fire Protection Testing and Certification Each listed assembly specifies the exact materials, thicknesses, and installation details required to achieve the stated rating. Deviating from a listed assembly, even by using a different thickness of gypsum board, can void the rating entirely.
Special Inspections During Construction
Type I projects require third-party special inspections for fire-resistive materials under IBC Section 1705. Qualified inspectors verify installation at multiple stages, not just at a final walkthrough.
For SFRM, Section 1705.15 requires inspection of the steel surface conditions before application, the application process itself, and the finished thickness of the coating. Thickness verification has separate criteria for standard members versus joists and trusses. After rough installation of electrical, mechanical, plumbing, and sprinkler systems, a follow-up visual inspection must confirm the SFRM hasn’t been damaged or displaced before it gets concealed behind finishes.
The inspector also conducts physical testing on the installed material. Density testing follows ASTM E605, and bond-strength testing follows ASTM E736. Both pull actual samples from the building to confirm the SFRM will perform as rated. If samples fail, the contractor must strip and reapply the affected areas.
Fire-resistant penetrations and joints have their own inspection requirements under Section 1705.18. Every firestop at a pipe, duct, or cable penetration must be inspected per ASTM E2174, and fire-resistive joint systems must be inspected per ASTM E2393.7ASTM International. ASTM E2393-20a Standard Practice for On-Site Inspection of Installed Fire Resistive Joint Systems and Perimeter Fire Barriers Missed firestops are one of the most common fire-rating failures inspectors find on site.
Maintaining the Rating After Occupancy
A fire-resistance rating is only as good as the fireproofing that delivers it, and SFRM is surprisingly fragile after installation. Plumbers, electricians, and other trades routinely damage spray-applied coatings when running pipes, pulling cable, or hanging equipment. Tenant improvements years after occupancy create the same problem. If damaged SFRM isn’t properly repaired, the structural member beneath has a lower rating than the building was designed for.
Most UL-listed SFRM assemblies limit hand-patching of damaged areas to a maximum of 144 square inches. Anything larger must either use the original product processed through a spray machine before hand-application, which reconstitutes the material’s spray-applied properties, or use a specialized patching product approved for larger areas. Some patching products are rated for hand application up to 432 square inches. Standard patching compounds applied beyond their listed limits do not restore the original fire rating, even if the repair looks complete.
Building owners should fold SFRM inspection and repair into their maintenance programs, particularly after any renovation that opens up ceilings or wall cavities.
Insurance Treatment
The Insurance Services Office classifies buildings into six construction classes for fire-rating purposes. Type I fire-resistive buildings receive the highest, Construction Class 6, which reflects the lowest expected fire loss.8Insurance Services Office. Fire Suppression Rating Schedule Property insurers use this classification when setting premiums, and the gap between Class 6 and lower classes, such as Class 1 for wood-frame or Class 3 for unprotected noncombustible, can be meaningful over the life of a building.
Those insurance savings help offset the higher construction cost over time. Type I buildings also tend to hold value more predictably. Institutional investors and REITs favor them because the noncombustible structure requires fewer major renovations to stay code-compliant as fire safety standards evolve. The combination of lower insurance costs, reduced catastrophic risk, and the ability to build to unlimited heights is what makes the upfront premium pencil out for most large-scale developers.