Building elements: The building materials used in the construction of the following elements are the foundation for classification, be they wood, steel, or masonry. Structural frame Exterior bearing walls Interior bearing walls Exterior nonbearing walls and partitions Interior non-bearing walls and partitions Floor construction, including supporting beams and joists Roof construction, including supporting beams and joists, are comprised of Fire-resistance rating: This 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 (ex. 0 hours, 1 hour, or 2 hours), or it may entail a host of other criteria involving other evidence of functionality or fitness for purpose. “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 (see below). 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 (see below).
Structural frame Exterior bearing walls Interior bearing walls Exterior nonbearing walls and partitions Interior non-bearing walls and partitions Floor construction, including supporting beams and joists Roof construction, including supporting beams and joists, are comprised of
“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 (see below). 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 (see below).
Structural frame Bearing walls (interior and exterior) Floor construction Roof construction What the fire rating of the materials
Frame Construction (ISO Class I, IBC Type V) Joisted Masonry (ISO Class 2, IBC Type III, IBC Type IV) Light Noncombustible (ISO Class 3, IBC Type IIB) Masonry Noncombustible (ISO Class 4, IBC Type IIA) Modified Fire Resistive (ISO Class 5, IBC Type IB) Fire Resistive (ISO Class 6, IBC Type IA)
International Building Code (IBC): This is a model building code developed by the International Code Council (ICC). It has been adopted throughout most of the United States. A large portion of the International Building Code deals with fire prevention. It differs from the related International Fire Code in that the IBC handles fire prevention in regards to construction and design and the fire code handles fire prevention in an ongoing basis. Parts of the code reference other codes including the International Plumbing Code, the International Mechanical Code, the National Electric Code, and various National Fire Protection Association Standards. 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. Insurance Services Office (ISO): This is a provider of data, underwriting, risk management, and legal/regulatory services to property-casualty insurers and other clients.
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.
Frame buildings are buildings with exterior walls, floors, and roofs with combustible construction — or buildings with exterior walls of noncombustible or slow-burning construction with combustible floors and roofs. Frame buildings generally have roof, floor, and supports of combustible material, usually wood, and combustible interior walls. Two variations on frame construction don’t change the construction class: Masonry veneer (brick veneer)- Masonry veneer is thin layers of brick, stone, or stucco, used for appearance purposes rather than structural support. Metal clad - A building with a metal exterior wall may not look like frame construction, but when the metal skin is attached to wood studs and joists, ISO classifies the building as frame. Other conditions that lead to classification as frame construction include: Metal walls or floors sheathed with combustible materials Metal floors or roofs with combustible insulation or ceiling material attached to the underside or within 18 inches (45. 7 cm) of horizontal supports Composite assemblies of noncombustible materials with combustible materials
easy to erect and alter economical versatile performs well in Earthquake areas – can move
fire can spread rapidly highly damageable may become unstable in a fire[2] X Research source may include enclosed spaces where fire can spread undetected
brick concrete — either reinforced or non reinforced hollow concrete masonry units tile stone note that exterior bearing walls may also be any noncombustible materials with fire-resistance ratings of not less than one hour
walls of masonry construction floors of 3 inch (7. 6 cm) wood plank or 4 inch (10. 2 cm) laminated plank, both surfaced with 1 inch (2. 5 cm) flooring roof of 2 inch (5. 1 cm) wood plank, 3 inch (7. 6 cm) laminated plank, or 1-1/8 inch tongue-and-groove plywood deck wood column supports not less than 8 inch (20. 3 cm) x 8 inch (20. 3 cm), wood beams or girders not less than 6 inch (15. 2 cm) x 6 inch (15. 2 cm), or protected metal
harder to ignite consumed more slowly by fire more structural stability greater salvage value lack of concealed spaces (Heavy Timber)
floors and roofs of combustible materials subject to damage by fire[4] X Research source presence of concealed spaces
buildings with exterior walls, floors, and roofs of noncombustible or slow-burning materials building supports of noncombustible or slow-burning materials noncombustible or slow-burning roof decks on noncombustible or slow-burning supports — regardless of the type of insulation on the roof surface
easy to erect economical to build uses materials that don’t readily burn
contains steel, which loses strength at high temperatures highly damageable buildings unstable buildings under fire conditions uses slow-burning materials that do burn — adding fuel to a fire
buildings with exterior walls of masonry — not less than four inches thick, or buildings with exterior walls of fire-resistive construction — with a rating of not less than one hour, and noncombustible or slow-burning floors and roofs — regardless of the type of insulation on the roof surface
Uses floors and roof supported by superior exterior bearing members that provide for stability and are less likely to collapse during a fire Uses materials that don’t readily burn
Uses unprotected steel for interior members of floors and roof, and steel loses strength and becomes less stable and more damageable at high temperatures[6] X Research source Uses slow-burning materials that do burn — adding fuel to a fire
Buildings with exterior walls, floors, and roofs of masonry materials described in the definition of fire resistive (Construction Class 6) — less thick than required for fire-resistive structures but not less than four inches thick, or Fire-resistive materials with a fire-resistance rating less than two hours but not less than one hour
Structural steel protection: Note that modified fire-resistive buildings also include structural steel protection techniques — fire-protection material applied to steel. Materials include: concrete plaster clay tile brick or other masonry units gypsum block gypsum wallboard mastic coatings mineral and fiberboard mineral wool Ceilings protecting steel beams or joists: What happens when there is no fire-protection material applied to steel beams or joists that support floors or roofs? ISO still considers a building modified fire resistive if it has a suitable ceiling. Ceilings can be plaster or gypsum wallboard or suspended mineral tile. The entire floor-ceiling (a fire-resistive ceiling protecting a floor) or roof-ceiling (a fire-resistive ceiling protecting roof supports) should conform to construction details in a UL-listed or Factory Mutual (FM)-approved design. ISO individually evaluates each approved design.
concrete plaster clay tile brick or other masonry units gypsum block gypsum wallboard mastic coatings mineral and fiberboard mineral wool
uses noncombustible materials[7] X Research source allows greater height and area than other construction classes uses load-bearing members or assemblies that resist damage from fire
expensive to construct and repair provides a false sense of security
Walls: solid masonry, including reinforced concrete not less than four inches thick hollow masonry not less than 12 inches (30. 5 cm) thick hollow masonry less than 12 inches (30. 5 cm) 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
uses noncombustible materials[8] X Research source allows greater height and area than other construction classes uses load-bearing members or assemblies that resist damage from fire
expensive to construct and repair provides a false sense of security
