IBC Type of Construction Guide (I-V)
Understanding the five construction types, fire-resistance requirements, and allowable heights/areas
What is Type of Construction?
Type of Construction classifies buildings based on the fire resistance of their structural elements. The IBC defines five main types (I through V), each with varying levels of fire protection. Higher numbers generally mean less fire resistance. Understanding construction type is essential when reviewing architectural drawings and verifying code compliance.
According to NFPA fire data, Type V (wood frame) buildings account for approximately 65% of all U.S. building fires but represent only 40% of fire-related property losses due to their smaller average size. Type I and II buildings, while less fire-prone, average $750,000 in damage per fire incident compared to $45,000 for Type V structures.
- • Maximum allowable building height (stories and feet)
- • Maximum allowable building area
- • Allowable occupancies
- • Fire separation requirements
- • Sprinkler and alarm requirements
Fire-Resistance Requirements by Type
| Type | Frame | Ext. Walls | Floors | Roof | Int. Bearing | Examples |
|---|---|---|---|---|---|---|
| Type I-A | Noncombustible | 3 hr | 2 hr | 1½ hr | 1 hr | High-rise buildings, hospitals |
| Type I-B | Noncombustible | 2 hr | 2 hr | 1 hr | 1 hr | Mid-rise buildings, schools |
| Type II-A | Noncombustible | 1 hr | 1 hr | 1 hr | 1 hr | Low-rise commercial, retail |
| Type II-B | Noncombustible | 0 hr | 0 hr | 0 hr | 0 hr | Warehouses, some retail |
| Type III-A | Ext. noncombustible, Int. any | 2 hr | 1 hr | 1 hr | 1 hr | Older mixed-use, apartments |
| Type III-B | Ext. noncombustible, Int. any | 2 hr | 0 hr | 0 hr | 0 hr | Small commercial |
| Type IV | Heavy Timber | 2 hr | HT | HT | 1 hr / HT | Mill construction, mass timber |
| Type V-A | Any material | 1 hr | 1 hr | 1 hr | 1 hr | Protected wood frame residential |
| Type V-B | Any material | 0 hr | 0 hr | 0 hr | 0 hr | Unprotected wood frame, single-family |
HT = Heavy Timber. Based on IBC Table 601.
Understanding Each Type
Highest level of fire protection. Structural elements are noncombustible (steel, concrete) with fire-resistive protection. Used for high-rise buildings, hospitals, and buildings requiring maximum occupant protection. These buildings must meet the most stringent fire-resistance rating requirements.
Structural elements are noncombustible but may or may not have fire-resistive protection. Type II-A is protected; Type II-B is unprotected steel or concrete. Common for commercial and industrial buildings.
Exterior walls are noncombustible (typically masonry or concrete); interior structure can be any material including wood. Common for "ordinary" construction like older commercial buildings.
Exterior walls are noncombustible; interior uses heavy timber (large wood members). The mass of heavy timber provides inherent fire resistance through charring. Now includes mass timber (CLT, glulam).
Any materials permitted including light wood frame. Type V-A has 1-hour protection; Type V-B is unprotected. Most residential construction is Type V-B.
Height & Area Modifications
The code allows increases to base height and area for several factors. These modifications interact with IBC occupancy classification to determine final allowable building size:
NFPA 13 sprinklers can increase stories by 1 and area by 200-300%
Open perimeter access for firefighting can increase area up to 75%
Certain combinations of sprinklers, frontage, and low-hazard uses allow unlimited area
Frequently Asked Questions
Both Type I-A and I-B are noncombustible construction, but Type I-A provides higher fire resistance ratings: 3-hour structural frame and exterior bearing walls vs. 2-hour for Type I-B. Type I-A is required for the tallest buildings (unlimited height when sprinklered), while Type I-B has a maximum height of 180 feet (12 stories) for most occupancies.
Yes. Type III construction requires noncombustible exterior walls only; interior structural elements can be any material including wood framing. This is common in older "mill construction" buildings with masonry exteriors and wood interior framing. The key requirement is that exterior walls be noncombustible (typically masonry, concrete, or steel).
NFPA 13 sprinklers provide significant increases per IBC Section 504.2 and 506.3: typically one additional story, 20 additional feet in height, and a 200-300% increase in allowable area per floor. For example, a Type V-A building (normally limited to 60 feet) can reach 80 feet when fully sprinklered. Review NFPA sprinkler requirements for detailed coverage.
Related Resources
Verify Construction Type Compliance
Articulate can review your drawings to verify that assemblies match the required construction type—checking rated walls, floor assemblies, and structural protection.
Try Automated Code ReviewSources & References
- • International Building Code (IBC) 2021, Chapter 6: Types of Construction
- • IBC 2021, Table 601: Fire-Resistance Rating Requirements for Building Elements
- • IBC 2021, Table 504.3: Allowable Building Height in Feet Above Grade Plane
- • IBC 2021, Table 504.4: Allowable Number of Stories Above Grade Plane
- • IBC 2021, Table 506.2: Allowable Area Factor
- • NFPA Fire Loss Statistics, U.S. Fire Administration (2023)
- • AWC/ICC DCA6: Design for Code Acceptance - Fire-Rated Wood Construction
Note: Local jurisdictions may have amendments to the IBC. Always verify requirements with your Authority Having Jurisdiction (AHJ).