Types of Construction

This chapter establishes the framework for classifying buildings based on their construction type and specifies the minimum fire-resistance ratings required for various building elements.

601 — General

601.1 Scope. The provisions of this chapter shall control the classification of buildings as to type of construction.

602 — Construction Classification

602.1 General. Buildings and structures erected or to be erected, altered or extended in height or area shall be classified in one of the five construction types defined in Sections 602.2 through 602.5. The building elements shall have a fire-resistance rating not less than that specified in Table 601 and exterior walls shall have a fire-resistance rating not less than that specified in Table 602. Where required to have a fire-resistance rating by Table 601, building elements shall comply with the applicable provisions of Section 703.2. The protection ofopenings, ducts and air transfer openings in building elements shall not be required unless required by other provisions ofthis code.

602.1.1 Minimum requirements. A building or portion thereof shall not be required to conform to the details of a type of construction higher than that type which meets the minimum requirements based on occupancy even though certain features of such a building actually conform to a higher type of construction.

602.1.1 Minimum requirements. A building or portion thereof shall not be required to conform to the details of a type of construction higher than that type which meets the minimum requirements based on occupancy even though certain features of such a building actually conform to a higher type of construction.

602.2 Types I and II. Types I and II construction are those types of construction in which the building elements listed in Table 601 are of noncombustible materials, except as permitted in Section 603 and elsewhere in this code.

602.3 Type III. Type III construction is that type of construction in which the exterior walls are of noncombustible materials and the interior building elements are of any material permitted by this code. Fire-retardant-treated wood framing complying with Section 2303.2 shall be permitted within exterior wall assemblies of a 2-hour rating or less.

602.4 Type IV. Type IV construction (Heavy Timber, HT) is that type of construction in which the exterior walls are of noncombustible materials and the interior building elements are of solid or laminated wood without concealed spaces. The

A table appears here in the adopted code. Refer to the official source for the full table.

details of Type IV construction shall comply with the provisions of this section. Fire-retardant-treated wood framing complying with Section 2303.2 shall be permitted within exterior wall assemblies with a 2-hour rating or less. Minimum solid sawn nominal dimensions are required for structures built using Type IV construction (HT) . For glued-laminated members the equivalent net finished width and depths corresponding to the minimum nominal width and depths of solid sawn lumber are required as specified in Table 602.4.

602.4.1 Columns. Wood columns shall be sawn or glued laminated and shall not be less than 8 inches (203 mm), nominal, in any dimension where supporting floor loads and not less than 6 inches (152 mm) nominal in width and not less than 8 inches (203 mm) nominal in depth where supporting roof and ceiling loads only. Columns shall be continuous or superimposed and connected in an approved manner. 602.4.2 Floor framing. Wood beams and girders shall be of sawn or glued-laminated timber and shall be not less than 6 inches (152 mm) nominal in width and not less than 10 inches (254 mm) nominal in depth. Framed sawn or glued-laminated timber arches, which spring from the floor line and support floor loads, shall be not less than 8 inches (203 mm) nominal in any dimension. Framed timber trusses supporting floor loads shall have members of not less than 8 inches (203 mm) nominal in any dimension. 602.4.3 Roof framing. Wood-frame or glued-laminated arches for roof construction, which spring from the floor line or from grade and do not support floor loads, shall have members not less than 6 inches (152 mm) nominal in width and have not less than 8 inches (203 mm) nominal in depth for the lower half of the height and not less than 6 inches (152 mm) nominal in depth for the upper half. Framed or glued-laminated arches for roof construction that spring from the top of walls or wall abutments, framed timber trusses and other roof framing, which do not support floor loads, shall have members not less than 4 inches (102 mm) nominal in width and not less than 6 inches (152 mm) nominal in depth. Spaced members shall be permitted to be composed of two or more pieces not less than 3 inches (76 mm) nominal in thickness where blocked solidly throughout their intervening spaces or where spaces are tightly closed by a continuous wood cover plate of not less than 2 inches (51 mm) nominal in thickness secured to the underside of the members. Splice plates shall be not less than 3 inches (76 mm) nominal in thickness. Where protected by approved automatic sprinklers under the roof deck, framing members shall be not less than 3 inches (76 mm) nominal in width.

602.4.1 Columns. Wood columns shall be sawn or glued laminated and shall not be less than 8 inches (203 mm), nominal, in any dimension where supporting floor loads and not less than 6 inches (152 mm) nominal in width and not less than 8 inches (203 mm) nominal in depth where supporting roof and ceiling loads only. Columns shall be continuous or superimposed and connected in an approved manner.

602.4.2 Floor framing. Wood beams and girders shall be of sawn or glued-laminated timber and shall be not less than 6 inches (152 mm) nominal in width and not less than 10 inches (254 mm) nominal in depth. Framed sawn or glued-laminated timber arches, which spring from the floor line and support floor loads, shall be not less than 8 inches (203 mm) nominal in any dimension. Framed timber trusses supporting floor loads shall have members of not less than 8 inches (203 mm) nominal in any dimension.

602.4.3 Roof framing. Wood-frame or glued-laminated arches for roof construction, which spring from the floor line or from grade and do not support floor loads, shall have members not less than 6 inches (152 mm) nominal in width and have not less than 8 inches (203 mm) nominal in depth for the lower half of the height and not less than 6 inches (152 mm) nominal in depth for the upper half. Framed or glued-laminated arches for roof construction that spring from the top of walls or wall abutments, framed timber trusses and other roof framing, which do not support floor loads, shall have members not less than 4 inches (102 mm) nominal in width and not less than 6 inches (152 mm) nominal in depth. Spaced members shall be permitted to be composed of two or more pieces not less than 3 inches (76 mm) nominal in thickness where blocked solidly throughout their intervening spaces or where spaces are tightly closed by a continuous wood cover plate of not less than 2 inches (51 mm) nominal in thickness secured to the underside of the members. Splice plates shall be not less than 3 inches (76 mm) nominal in thickness. Where protected by approved automatic sprinklers under the roof deck, framing members shall be not less than 3 inches (76 mm) nominal in width.

A table appears here in the adopted code. Refer to the official source for the full table.

602.4.4 Floors. Floors shall be without concealed spaces. Wood floors shall be of sawn or glued-laminated planks, splined or tongue-and-groove, of not less than 3 inches (76 mm) nominal in thickness covered with I-inch (25 mm) nominal dimension tongue-and-groove flooring, laid cross-wise or diagonally, or 0.5-inch (12. 7 mm) particleboard or planks not less than 4 inches (102 mm) nominal in width set on edge close together and well spiked and covered with I-inch (25 mm) nominal dimension flooring or 15/32-inch (12 mm) wood structural panel or 0.5-inch (12.7 mm) particleboard. The lumber shall be laid so that no continuous line of joints will occur except at points of support. Floors shall not extend closer than 0.5 inch (12.7 mm) to walls. Such 0.5-inch (12.7 mm) space shall be covered by a molding fastened to the wall and so arranged that it will not obstruct the swelling or shrinkage movements of the floor. Corbeling of masonry walls under the floor shall be permitted to be used in place of molding. 602.4.5 Roofs. Roofs shall be without concealed spaces and wood roof decks shall be sawn or glued laminated, splined or tongue-and-groove plank, not less than 2 inches (51 mm) nominal in thickness, 11/s-inch-thick (32 mm) wood structural panel (exterior glue), or of planks not less than 3 inches (76 mm) nominal in width, set on edge close together and laid as required for floors. Other types of decking shall be permitted to be used if providing equivalent fire resistance and structural properties. 602.4.6 Partitions. Partitions shall be of solid wood construction formed by not less than two layers of I-inch (25 mm) matched boards or laminated construction 4 inches (102 mm) thick, or of I-hour fire-resistance-rated construction. 602.4.7 Exterior structural members. Where a horizontal separation of 20 feet (6096 mm) or more is provided, wood columns and arches conforming to heavy timber sizes shall be permitted to be used externally.

602.4.4 Floors. Floors shall be without concealed spaces. Wood floors shall be of sawn or glued-laminated planks, splined or tongue-and-groove, of not less than 3 inches (76 mm) nominal in thickness covered with I-inch (25 mm) nominal dimension tongue-and-groove flooring, laid cross-wise or diagonally, or 0.5-inch (12. 7 mm) particleboard or planks not less than 4 inches (102 mm) nominal in width set on edge close together and well spiked and covered with I-inch (25 mm) nominal dimension flooring or 15/32-inch (12 mm) wood structural panel or 0.5-inch (12.7 mm) particleboard. The lumber shall be laid so that no continuous line of joints will occur except at points of support. Floors shall not extend closer than 0.5 inch (12.7 mm) to walls. Such 0.5-inch (12.7 mm) space shall be covered by a molding fastened to the wall and so arranged that it will not obstruct the swelling or shrinkage movements of the floor. Corbeling of masonry walls under the floor shall be permitted to be used in place of molding.

602.4.5 Roofs. Roofs shall be without concealed spaces and wood roof decks shall be sawn or glued laminated, splined or tongue-and-groove plank, not less than 2 inches (51 mm) nominal in thickness, 11/s-inch-thick (32 mm) wood structural panel (exterior glue), or of planks not less than 3 inches (76 mm) nominal in width, set on edge close together and laid as required for floors. Other types of decking shall be permitted to be used if providing equivalent fire resistance and structural properties.

602.4.6 Partitions. Partitions shall be of solid wood construction formed by not less than two layers of I-inch (25 mm) matched boards or laminated construction 4 inches (102 mm) thick, or of I-hour fire-resistance-rated construction.

602.4.7 Exterior structural members. Where a horizontal separation of 20 feet (6096 mm) or more is provided, wood columns and arches conforming to heavy timber sizes shall be permitted to be used externally.

602.5 Type V. Type V construction is that type of construction in which the structural elements, exterior walls and interior walls are of any materials permitted by this code.

Worked example

Scenario: An architect is designing a new 10-story office building and needs to determine its construction classification.

Explanation: To classify the building, the architect must review the required fire-resistance ratings for elements like the structural frame, floor construction, and exterior walls as specified in Table 601. These ratings will then align the building with one of the five construction types defined in Sections 602.2 through 602.5.

603 — Combustible Material in Type I and Ii Construction

603.1 Allowable materials. Combustible materials shall be permitted in buildings ofType I or II construction in the following applications and in accordance with Sections 603.1.1 through 603.1.3:

Thermal and acoustical insulation, other than foam plastics, having a flame spread index of not more than25. Exceptions: Insulation placed between two layers of noncombustible materials without an intervening airspace shall be allowed to have a flame spread index of not more than 100. Insulation installed between a finished floor and solid decking without intervening airspace shall be allowed to have a flame spreadindex of not more than 200.
Foam plastics in accordance with Chapter 26 .
Roof coverings that have an A, B or C classification.
Interior floor finish and floor covering materials installed in accordance with Section 804.
Millwork such as doors, door frames, window sashes and frames.
Interior wall and ceiling finishes installed in accordance with Sections 801 and 803.
Trim installed in accordance with Section 806.
Where not installed over 15 feet (4572 mm) above grade, show windows, nailing or furring strips and wooden bulkheads below show windows, including their frames, aprons and show cases.
Finish flooring installed in accordance with Section 805.
Partitions dividing portions of stores, offices or similar places occupied by one tenant only and that do not establish a corridor serving an occupant load of 30 or more shall be permitted to be constructed of fire-retardant-treated wood, I-hour fire-resistance-rated construction or ofwood panels or similar light construction up to 6 feet (1829 mm) in height.
Stages and platforms constructed in accordance with Sections 410.3 and 410.4, respectively.
Combustible exterior wall coverings, balconies and similar projections and bay or oriel windows in accordance with Chapter 14.
Blocking such as for handrails, millwork, cabinets and window and door frames.
Light-transmitting plastics as permitted by Chapter 26.
Mastics and caulking materials applied to provide flexible seals between components of exterior wall construction.
Exterior plastic veneer installed in accordance with Section 2605.2.
Nailing or furring strips as permitted by Section 803.4.
Heavy timber as permitted by Note c to Table 601 and Sections 602.4.7 and 1406.3.
Aggregates, component materials and admixtures as permitted by Section 703.2.2.
Sprayed fire-resistant materials and intumescent and mastic fire-resistant coatings, determined on the basis of fire-resistance tests in accordance with Section 703.2 and installed in accordance with Sections 1704.12 and 1704.13, respectively.
Materials used to protect penetrations in fire-resistance-rated assemblies in accordance with Section 713.
Materials used to protect joints in fire-resistance-rated assemblies in accordance with Section 714.
Materials allowed in the concealed spaces of buildings of Types I and II construction in accordance with Section 717.5.
Materials exposed within plenums complying with Section 602 of the International Mechanical Code.
1. Fire-retardant-treated wood shall be permitted in: 25.1. Nonbearing partitions where the required fire-resistance rating is 2 hours or less. 25.2. Nonbearing exterior walls where no fire rating is required. 25.3. Roof construction, including girders, trusses, framing and decking. Exception: In buildings of Type IA construction exceeding two stories above grade plane, fire-retardant-treated woodis not permitted in roof construction when the vertical distance from the upper floor to the roof is less than 20 feet (6096 mm).

Exceptions:

Insulation placed between two layers of noncombustible materials without an intervening airspace shall be allowed to have a flame spread index of not more than 100.
Insulation installed between a finished floor and solid decking without intervening airspace shall be allowed to have a flame spreadindex of not more than 200.

25.1. Nonbearing partitions where the required fire-resistance rating is 2 hours or less.

25.2. Nonbearing exterior walls where no fire rating is required.

25.3. Roof construction, including girders, trusses, framing and decking.

Exception: In buildings of Type IA construction exceeding two stories above grade plane, fire-retardant-treated woodis not permitted in roof construction when the vertical distance from the upper floor to the roof is less than 20 feet (6096 mm).

603.1.1 Ducts. The use of nonmetallic ducts shall be permitted when installed in accordance with the limitations of the International Mechanical Code.

603.1.2 Piping. The use of combustible piping materials shall be permitted when installed in accordance with the limitations of the International Mechanical Code and the International Plumbing Code.

603.1.3 Electrical. The use of electrical wiring methods with combustible insulation, tubing, raceways and related components shall be permitted when installed in accordance with the limitations of this code.

Worked example

Scenario: For a Type I-A hospital project, the design includes extensive decorative wood trim and non-load-bearing partition walls made of gypsum board over wood studs.

Explanation: Section 603.1 allows combustible materials in Type I and II buildings for certain applications, such as interior finishes and non-load-bearing elements. The architect must ensure these materials, including the wood trim and wood-stud partitions, meet the specific requirements of Sections 603.1.1 through 603.1.3, which cover limitations on flame spread, thickness, and concealed spaces.

Frequently asked questions

How are buildings classified by construction type?

Buildings are classified into one of five construction types based on the fire-resistance ratings of their building elements, as specified in Table 601 and defined in Sections 602.2 through 602.5.

Can combustible materials be used in Type I or Type II buildings?

Yes, combustible materials are permitted in Type I or II construction for specific applications, provided they comply with the provisions outlined in Sections 603.1.1 through 603.1.3.