Construction types
Fire Resistive (ISO Class 6, IBC Type IA)
Fire Resistive construction is ISO Class 6. ISO Class 6 encompasses IBC Type IA.
Learn the elements of Fire Resistive Construction. The exterior bearing walls and load-bearing portions of exterior walls must be of noncombustible materials or of masonry, but exterior nonbearing walls and wall panels may be slow burning, combustible, or with no fire-resistance rating.
Walls:
solid masonry, including reinforced concrete not less than four inches thick
hollow masonry not less than 12 inches thick
hollow masonry less than 12 inches thick, but not less than eight inches thick with a listed fire-resistance rating of not less than two hours
assemblies with not less than a two-hour fire-resistance rating
Floors and roofs:
reinforced concrete not less than four inches thick
assemblies with not less than a two-hour fire-resistance rating
Structural metal supports:
Horizontal and vertical load-bearing protected metal supports — including pre stressed and post tensioned concrete units — with not less than a two-hour fire-resistance rating
Pre- and Post tensioned Concrete
Both pre- and post tensioned concrete units have steel cables installed in the concrete to provide tensile strength. With pre stressed concrete units, builders pull the cables tight before pouring the concrete and release them as the concrete cures. With post tensioned concrete units, builders pull one end of the cable tight after pouring the concrete.
Note the fire resistive advantages:
uses noncombustible materials
allows greater height and area than other construction classes
uses load-bearing members or assemblies that resist damage from fire
Note that fire-resistive construction has these disadvantages:
expensive to construct and repair
provides a false sense of security
IBC is more descriptive and also includes A or B types of construction for each class.
A is protected, meaning that all structural members of a building or structure have an additional fire rated coating or cover by means of sheetrock, spray on, or other approved method. The additional fire rated coating or cover extends the fire resistance of the structural members by at least 1 hour.
B is unprotected, meaning that all structural members of a building or structure have no additional fire rated coating or cover. Exposed members are only fire resistant according to their natural ability, characteristics, and fire rating.
How to Classify a Building Class? As stated in the introduction, all buildings must be classified into one of the 6 ISO construction classes. Classification of a building class is based on two factors; Building Elements and Fire Resistance Rating. These factors may not be included in the submission and additional information will need to be requested.
First classification is based on the following building elements:
- Structural frame,
- Exterior bearing walls,
- Interior bearing walls,
- Exterior nonbearing walls and partitions,
- Interior nonbearing walls and partitions,
- Floor construction including supporting beams and joists,
- Roof construction including supporting beams and joists are comprised of.
The building materials used in the construction of the above elements are the foundation for classification, be it wood, steel, or masonry.
Fire-Resistance Rating is the other factor in determining construction class. The building materials used in the construction of the building elements above will have a fire-resistance rating. Fire-Resistance rating typically means the duration for which a passive fire protection system can withstand a standard fire resistance test. This can be quantified simply as a measure of time, or it may entail a host of other criteria, involving other evidence of functionality or fitness for purpose.
The building materials and building elements must meet the fire-resistance rating criteria for the construction class selected. Fire-resistance rating can simply be 0 hours, 1 hour, or 2 hour.
Minimum Rule – It is important to remember when selecting the construction class that the building is only as strong as its weakest element. For example, a masonry building may have an unprotected wood roof. The wood roof is the weakest member such that it has no fire-resistance. Thus the construction class would be Joisted Masonry. Now imagine this same building with a metal deck roof. So long as the supporting members of the building do not contain wood then this building would be Masonry Noncombustible.
What to ask? To determine the ISO Class of the building we must know the following composition of the building elements:
Structural frame?
Bearing walls (interior and exterior)?
Floor construction?
Roof Construction?
What is the fire rating of the materials?