IBC 2006 Chapter 6 Types of Construction

1. Session 9 | Codes | Gary Parker IBC 2006 Chapter 6 Types of Construction This chapter of IBC has improved earlier definitions of types of construction by indicating performance criteria as per tests, rather than the previous prescriptive sections related to known fire-resistance ratings of known materials. This has added some degree of confusion with regard to the interpretation of material qualities in contrast to earlier code provisions that prescribed what kinds of materials to use. The new code criteria define the subdivision of materials between combustible and non-combustible by their test under given conditions. `

2. Types of Construction The IBC classifies all buildings into 5broadcategoriesbased on the fire-resistance capabilities of the predominant materials used for their construction. The 5 types of construction are given Roman-numeral designations, and progress downward in fire-resistance from Type I, the most fire-resistive construction, to Type V, the least fire-resistive. The 5 types of construction classes are subdivided into 2 broad categories, A and B, based upon their inherent fire-resistance or combustibility of the materials; these are further subdivided according to the fire-resistance gained by the application of protection to major elements of the construction systems. Table 503 correlates the five types of construction with the allowable heights and areas for buildings based on their occupancy.

3. Table 503

4. Construction Classification Table 601 defines the required fire-resistance of major building elements for each type of construction. However, Chapter 7 governs the actual materials and assemblies used in fire-resistance rated construction. There is a direct relationship between occupancy type and the number of occupants to the construction classification. Higher occupant quantities, more hazardous occupancies and occupants with special needs, require more fire resistance or additional levels of active fire-suppression systems.

5. Construction Classification Noncombustible Materials The principal elements of construction Type I and II are made of noncombustible materials. According to the UBC, noncombustible is defined as a material of which no part will ignite and burn when subjected to fire (UBC 1997, §215). The IBC definition of noncombustibility is containedin §703.4 and states that materials required to benoncombustible must meet the test criteria prescribed in the American Society for Testing and Materials ASTM Standard E 136. Noncombustible materials include masonry, concrete and steel. The application of additional fire protection materials to the noncombustible elements of Type I and II constructions yields higher Type I-A, I-B and II-A ratings above the basic Type II-B classification for unprotected noncombustible construction.

6. Construction Classification Combustible Materials The elements of Type III, IV and V constructionallow the use of combustible materials in varying degrees. Additional levels of fire protection can increase the fire-resistance rating of these three types of construction. The types with mixed elements of combustible and noncombustible materials are considered combustible and belong to Type III, IV and V. There is no definition of combustible construction contained in the IBC. By inference, these materials will be those that do not comply with the requirements contained in ASTM E 136, such as wood and plastics.

7. Passive Fire Protection The principle of fire-resistance is based on the desire to limit the spread of fire from: One building to another One area to another One floor to another

8. Passive Fire Protection The requirements for the fire-resistance of internal building elements are based on the theory of compartmentalization. The idea is to divide a building into distinct zones with barriers to delay the propagation and spread of fire

9. Passive Fire Protection Table 601 specifies the required fire-resistance ratings of major building elements for the 5 types of construction. The fire-resistance of building elements gives occupants time to leave the building in the event of an emergency and allow fire fighters time to fight the fire by delaying structural failure. The categories of building elements are: structural frame bearing walls nonbearing walls & partitions floor construction roof construction

10. Passive Fire Protection There exists a direct relationship between providing fire-protection and cost of construction, hence, most bldg. owners would opt for the lowest fire-resistance rating as possible. The building is analyzed as whole to determine compliance to the code provisions with regard to the fire-protection, and is thus considered in aggregate. Table 503 recognizes the fact that as fire-resistance rating is increased by means of the application of fire-retardant coverings, increases in building areas and heights are possible. The application of passive fire-resistive materials may increase the durability of even noncombustible materials in a fire. Even steel loses its strength in a fire.

11. Table 601 Table 601 specifies the fire-resistance ratings requirements for the major building elements, based on a specified type of construction or construction classification. A building may only be classified as a single type of construction unless a fire wall divides it into separate structures. Even if some building elements satisfy criteria for a higher type of construction, the building as a whole need only conform to the lowest type that meets the required criteria based on occupancy.

12. Table 601 Footnotes Footnote (a) - Includes the definitions of what constitutes the structural frame. Only those primarily elements framing directly into the columns need meet the protection criteria noted. Other elements are covered by the requirements for floor and roof construction.

13. Table 601 Footnotes Footnote (c) – Refers to special provisions for fire protection and element protection in roof constructions. C1 – permits unprotected roofs for height > 20’ except Group F, H, M and S-1 C2 – allows the usage of HT where 1hr or less of fire resistance rating is required C3 – allows the use of fire-retardant-treated wood in Type I and II construction for bldg. height not over 2 stories.

14. Table 601 Footnotes Footnote (d) – states trade-off provisions for the use of automatic fire-sprinkler systems to compensate for the diminution of protection of the building elements in buildings of 1 hr rated construction. These trade-offs are used only when the sprinkler system is not otherwise required by the code and is not being used to augment other considerations such as allowable area or height.

15. Table 601 Footnotes Footnote (e) – refers back to a specific provision for interior non-bearing partitions for Type IV buildings as spelled out in the detailed parts of §602.4.6 Footnote (f) – advises designers to compare the requirements of both Table 601 and Table 602 to determine the fire-resistive requirements for exterior bearing walls. In case of overlapping requirements use provisions under §102.1 Case: Group M occupancy in a Type V-A building located within 5’ of property line would require a 2hr wall rating per Table 602 and only a 1hr rating per Table 601. In this case the 2hr requirement would govern, as the code requires the most restrictive provision to govern.

16. Table 602 Table 602 specifies the fire-resistance rating requirements of exterior walls based on fire-separation distance as well as type of constructionandoccupancy groups. The use of table requires the occupancy group to be known in order to determine the fire-resistance requirements of exterior walls.

17. Table 602 Fire separation distance is a new term that replaces the terminology ‘location on property’. This not only addresses the spatial relationship of buildings to their site boundaries but also to the adjacent buildings on the same site. There in an interrelationship between building occupancy, construction type and location on site. These are dependent variables each impacting the others as the building develops.

18. Table 602 The fire-resistance requirements decrease with increasing distance between buildings. They also decrease in relation to decreasing construction-type requirements. The guiding principle of Table 602 is that increased distances offset the hazards presented by various occupancies. Distance also mitigates the reduction in resistance to external fires presented by less restrictive construction types.

19. Table 602 The amount of opening area in exterior walls is governed by the area limitations set forth in Table 704.8. The opening protection levels are correlated between the wall protection requirements of Table 602 and the opening protection requirements of Table 714.2. The designer must first ascertain the required fire-resistance rating of exterior walls to determine the required level of opening protection in the exterior walls. The designer can then determine the allowable amount of protected and unprotected openings in the exterior wall by using these sections together.