IBC 2006 Chapter 6 Types of Construction (cont’d)

1. Session 10 | Codes | Gary Parker IBC 2006 Chapter 6 Types of Construction (cont’d)

2. Types of Construction

3. Types I and II of Construction The building elements of Type I and Type II construction are of noncombustible materials. The definition of noncombustible material is contained in §703.4 and requires meeting the criteria of ASTM E 136. Type I-A, providing the highest level of fire-resistance-rated construction, requires passive protection for all elements of the structure Type I-B is similar to Type I-Am but permits a 1-hr reduction in fire-resistance rating for the structural frame, bearing walls and floor construction, and a ½ hr reduction for roof construction. Type II-A construction allows active or passive protection of all elements of the structure. Type II-B construction allows unprotected noncombustible building elements. Before this was described as ‘Type II nonrated”.

4. Combustible Materials in Types I and II Construction The key to the use of combustible materials in a noncombustible construction type is understanding that these uses are ancillary to the primary structure of the building. The premise for allowing the use of these combustible materials is that they will be of limited quantity and used under defined conditions where they will not contribute in any large measure to compromising the desired level of fire-resistance in the structure. There are a number of exceptions providing the use of combustible materials in Type I and Type II constructions.

5. Exceptions for Combust. Materials in Type I and Type II § 603 contains a list of notes specifying which combustible materials can be used in buildings of Type I and Type II constructions. 1 Reiterates allowances for the use of fire-retardant-treated FRT wood for non-bearing walls and partitions and for the roof construction noted in the footnotes of Table 601. 2 Materials with a flame spread of less than 25 have ratings corresponding to Class A interior finishes per ASTM E 84. These indices may be higher, as noted in the exception, where insulation is encapsulated between layers of noncombustible materials without an air space. 3 Foam plastics are allowable of complaint with the provisions of Chapter 26 of the IBC. 4 Most of roof coverings have a classification or A, B or C, so this should almost always be workable.

6. Exceptions for Combust. Materials in Type I and Type II 5 IBC recognizes that combustible decorative and utilitarian interior finishes such as wood floors, will be applied over the noncombustible structural elements. 6 Wood trim at or near grade level is acceptable if it is not beyond ready fire-fighting access up to a level of 15’ above grade.. 7 Fire-stopping is required in wood floors in Type I and II construction. 8 The key to this section is that the area in question be occupied and controlled by a single tenant. Also, these partitions must not define exit access passages that could be construed as corridors for the use of more than 30 occupants. Single tenant floors can have partitions of wood or similar light construction if they are lower than 6’ and allow standing occupants to generally survey the occupied space in the event of emergency. 9 Platforms are defined in §410 as raised areas used for worship, lectures, music plays or other entertainment.

7. Exceptions for Combust. Materials in Type I and Type II 10 These refer to incidental materials defined in §602 of IMC. 11 Provisions from Chapter 14, Chapter 26 and Chapter 7 that regard the fire-separation and fire-resistive properties of combustible veneers in projections from exterior walls. 12 Combustible blocking and nailers are incidental to the structural fire-resistance of the building as a whole. This note acknowledges the necessity for their usage. 13 Plastic glazing materials are permitted in conformance with the requirements of Chapter 26. 14 Similar to Note 12 15 Decorative plastic veneer is allowable if installed in accordance with requirements of Chapter 26.

8. Exceptions for Combust. Materials in Type I and Type II 16 Similar to Note 12. 17 This is a cross-reference to Footnote C of Table 601 and is redundant. 18 These aggregates are allowed to be combustible provided that the assembly meets the fire-resistance-test criteria of the IBC. 19-22 These exceptions allow for combustible materials to be used if they meet specific criteria spelled out in other sections of the IBC.

9. Exceptions for Combust. Materials in Type I and Type II

10. Type III Construction Type III buildings are a mix of noncombustible and combustible elements, having noncombustible exterior walls and combustible interior construction. These building types arose in the US in late 1800s out of the need to end conflagrations that struck congested business districts such as Chicago. The buildings were designed to prevent a fire from spreading from one building to another by igniting the exterior wall of adjacent buildings.

11. Type III Construction Type III buildings are a mix of noncombustible and combustible elements, having noncombustible exterior walls and combustible interior construction. These building types arose in the US in late 1800s out of the need to end conflagrations that struck congested business districts such as Chicago. The buildings were designed to prevent a fire from spreading from one building to another by igniting the exterior wall of adjacent buildings.

12. Type III Construction The construction materials on the exterior of a Type III building are required to be of noncombustible materials. FRT wood is allowable in the exterior walls where the required fire-resistance rating is 2 hrs or less. Table 601 requires 2hr walls for Type III-A buildings, thus FRT wood is acceptable except where this is superseded by the requirements of Table 602 based on the fire separation distance. This would only occur in Group H occupancies with a fire-separation distance of of less than 5’. Type III buildings are considered combustible since the IBC allows their interior building elements to be of combustible materials and also to be of unprotected construction of allowed by the building height and area allowances based on occupancy.

13. Type IV Construction Type IV buildings came about to address fire-safety conditions for manufacturing and storage, as Type III did for office and residential occupancies. It is also known as ‘mill construction’. They utilized heavy timber HT structural members and heavy wood floor decking inside of exterior walls of noncombustible construction. Many of these buildings have also movable heavy metal shutters to close off exterior openings to prevent a fire to propagate from outside or into the neighboring building.

14. Type IV Construction The criteria for HT construction are based on the past performance of historical construction, not on the scientific rationales of ASTM E 136 and E 119. Type III buildings burn slower under fire conditions. As the charring of the HT members continues, it retards further deterioration of the wood members by insulating the core of the wood from the fire. This type of construction utilizes heavy-sawn timbers in older buildings, but likely will use glued-laminated structural wood members in modern construction.

15. Type IV Construction A key element of HT construction is that there are no concealed spaces in the building elements. This prevents the development of unobserved fires. This would prevent sudden structural collapse. Lumber sizes are called out as nominal, hence the actual dimensions of wood members will be smaller. Ex. 8”x8” nominal = 7 ¼”x7 ¼” actual. Floor framing requires a minimum nominal thickness of 3” and floor are required to be held away from the exterior wall but blocked with fire-blocking or corbeling under floor members. Sprinkler substitutions criteria for the roof of HT buildings are contained in §602.4.3 and not called in footnote d of Table 601 like other constructions. Also, the separation criteria for HT buildings are noted in § 602.4.7 and not in Table 602 like other types of construction.

16. Type V Construction Type V construction is the least restrictive construction type. It allows the use of any materials permitted by the IBC. A typical example is the conventional light-wood-framed single family residence. Due to the fact that elements are combustible, the fire resistance of building elements is typically provided by the application of fire-resistance materials to the building parts. Type V-A construction is a protected construction, hence all major building elements must have a 1hr rating. Type V-B construction is unprotected and requires no fire-resistance ratings except where §602.1 and Table 602 require exterior wall protection.