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Engineering Manual

Construction Classifications

Effective: January 2006 Rev 001


One of the major considerations in the underwriting of any risk for property coverage is the combustibility and the resistance of the building to fire. A building of concrete and steel is obviously more resistant to fire than is one of wood or wood and masonry construction.

Thecommon building types described in this document are generally recognized but there are variations between tariff organizations in classification of construction in the rating schedules. Thus, while all organizations may agree on the term “fire-resistive” for buildings meeting certain specifications, they may not be uniform in the classification of such buildings. The classification letters AA, A,B, C and D described in this document are used to indicate the type of construction and to form the basis for determining rate adequacy and net retention for AIG.

There are occasions when there will be several buildings of varying construction on the same site. The engineer should rate the overall construction standard in conjunction with the MAS range i.e. if the main building is re-inforcedconcrete construction but there are several timber out-buildings on the perimeter of a site, but not affecting the MAS range, the overall construction should not be downgraded.

A single building must attract one overall construction standard – there should not be a percentage split if there is more than one construction class. There is a maximum of 15% deviation permitted subject to engineeringjudgement (refer Mixed Construction section of this document). The lowest construction standard should be adopted, although if the engineer feels that this is punitive he/she should speak with the underwriter.

Building Classification

Class “AA” Buildings (see Example 1). Class AA buildings are characterized by a frame of reinforced concrete, as opposed to the protected steel frame of Class Abuildings. Columns and beams may be poured or pre-cast.

The floors and roofs of Class AA buildings are reinforced concrete and the exterior walls may be of brick, hollow concrete block, concrete or other incombustible material. Unlike walls on Class A buildings, Class AA building walls may be load-bearing or partially load-bearing. Interior walls and partitions are of masonry, steel or otherincombustible material.

The term “fire resistive” is commonly used for Class AA as well as Class A buildings. The use of this term implies a construction totally comprised of noncombustible materials and which will withstand the most severe internal fire that can be expected for two or more hours without structural failure.

All structural members-walls, partitions, columns, floors and roofsmust have appropriate fire resistance ratings.

Example 1 – Examples of Class AA Construction

Class “A” Building (see Example 2). The primary feature of Class A buildings is the fireproofed steel frame. The fireproofing may be brick, poured concrete, plaster, sprayed composite or other type of protection which provides a high degree of resistance to fire. The floors and roofs of Class Abuildings are usually constructed of reinforced concrete on protected steel decking and are supported by the steel frame. The exterior walls are brick, concrete, or one of the many types of panels of metal, glass, concrete or other materials. Such walls, commonly referred to as “curtain” walls, bear none of the load of the building itself, this being the feature of the steel frame.

Interiorpartitions are of masonry, gypsum block or metal.

Class A buildings are commonly referred to as “fireproof”, or preferably, “fire resistive.”

Example 2a – Detailed diagrams of fireproofed steel

Example 2b – diagram of fireproofed steel frame with reinforced concrete floors
Class “B” Building Classification (see Example 3). Class B buildings are those which are incombustible in nature but do not...
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