Types of Construction

Types of Construction

Learning Objectives

By the end of this chapter, you should be able to:

1.1 The Foundation: Why Type of Construction Matters

The type of construction is the single most important classification for a building inspector after the occupancy group. It determines the building's allowable height, area, and the level of fire resistance required for its structural components. The International Building Code (IBC) establishes this framework in Chapter 6.

The fundamental principle is simple: The more fire-resistant the construction, the larger and taller the building may be. A building constructed of protected noncombustible materials (Type I) can be significantly larger than one built of unprotected wood (Type V). The code balances the risk of fire spread and structural collapse against the need for building size and function.

For the B2 exam, you must be able to look at a building's description and correctly classify it, and conversely, look at a classification and know the minimum fire-resistance requirements for its parts.

1.2 The Five Types and Their Subtypes

The IBC defines five basic types of construction, with subtypes "A" (protected) and "B" (unprotected) for Types I, II, III, and V. Type IV is unique and does not have A/B subtypes in the traditional sense.

Type I (Fire-Resistive): The most restrictive and fire-resistant type. Structural members, including columns, beams, girders, and trusses, are of noncombustible materials with high fire-resistance ratings (typically 2 to 3 hours). This type is used for high-rise buildings and large-area structures.

Type II (Noncombustible): Structural members are of noncombustible materials, but with lower fire-resistance ratings than Type I. Type II-B is often called "unprotected noncombustible" because the structural frame has no required fire-resistance rating. Type II-A requires a 1-hour rating on the structural frame.

Type III (Ordinary): Exterior walls are of noncombustible materials (e.g., masonry, concrete) with a fire-resistance rating (typically 2 hours). The interior structural elements (floors, roof, interior walls, and framing) may be of combustible materials (wood). This is the classic "brick and joist" building.

Type IV (Heavy Timber, HT): Exterior walls are noncombustible with a 2-hour fire-resistance rating. Interior structural elements are of solid or laminated wood with minimum dimensions (e.g., columns not less than 8 inches in any dimension, beams not less than 6 inches wide and 10 inches deep). The large cross-sections are designed to char at a predictable rate, maintaining structural integrity during a fire. There are no A/B subtypes; all Type IV is considered protected.

Type V (Wood-Frame): Both exterior walls and interior structural elements are of combustible materials. Type V-A requires a 1-hour fire-resistance rating on the structural frame and walls. Type V-B is "unprotected" wood frame with no fire-resistance rating required for the structural frame.

1.3 The Key Table: Table 601

Table 601 is the heart of Chapter 6. It lists the minimum fire-resistance ratings (in hours) for the following building elements, based on the type of construction:

You must memorize the general pattern of this table, not the exact numbers. The pattern is:

*HT = Heavy Timber; specific minimum dimensions apply, not hourly ratings.

Critical Observations for the Exam:

1.4 Understanding the Footnotes and Exceptions

Table 601 is riddled with footnotes that are just as important as the table itself. The exam will test your ability to apply these exceptions. You must know the general intent of each footnote.

Footnote "a" – Roof Construction: This is the most tested footnote. It states that roof construction, including the structural frame, may be reduced to a 1-hour rating (or even 0 hours for Type II-B and V-B) if certain conditions are met. These conditions typically include:

Footnote "b" – Structural Frame: This footnote clarifies that the structural frame rating applies to the members that support the building's weight. It specifically excludes certain elements like:

Footnote "c" – Exterior Walls: This footnote allows for a reduction in the fire-resistance rating of exterior bearing walls based on the fire separation distance (the distance from the building to the property line or centerline of a public way). The farther the building is from the property line, the lower the required rating can be. This is a complex provision that requires referencing Table 602.

Footnote "d" – Interior Bearing Walls: This footnote allows the interior bearing walls of a building to have a lower rating if they are part of a building that is protected by an automatic sprinkler system. The reduction is typically 1 hour, but the rating cannot be reduced below 1 hour for Type I and II construction.

Footnote "e" – Type IV Construction: This footnote specifies the minimum dimensions for heavy timber members. For example, columns must be at least 8 inches in any dimension, and beams must be at least 6 inches wide and 10 inches deep.

Footnote "f" – Type II-B and V-B: This footnote clarifies that for these unprotected types, the "0" rating means no fire-resistance rating is required, but the materials must still comply with the noncombustible (Type II) or combustible (Type V) material requirements.

1.5 Code Navigation: Where to Find It

For an open-book exam, knowing where to look is half the battle. Here is your navigation map for this chapter's content:

Exam Strategy: When you see a question about a fire-resistance rating, your first action should be to flip to Table 601. Then, check the footnotes for any exceptions that might apply. If the question involves exterior walls, you must also check Table 602.

1.6 Practical Inspection Points

As a Commercial Building Inspector, you are not just reading plans; you are verifying that the constructed building matches the approved plans and the code. Here is what you look for on site:

1.7 The Interplay with Height and Area

The type of construction is not an isolated concept. It directly controls the building's maximum allowable height (in feet and stories) and floor area. This is covered in Chapter 5.

Key Exam Point: The "A" (protected) subtypes always allow for a taller and larger building than the "B" (unprotected) subtypes of the same type. This is a direct result of the increased fire resistance.

1.8 Summary of Key Concepts

Mastering this chapter is essential. You will use this knowledge on nearly every question involving building size, egress, or fire protection. Know Table 601 and its footnotes cold, and you will be well on your way to passing the B2 exam.