IBC and ISO Classification

Construction types

Protected “A” means that all structural members of a building or structure has additional fire rated coating or cover by means of sheetrock, spray on, or other approved method. This additional fire rated coating or cover extends the fire resistance rating of structural members at least 1 hour.
Un-protected “B” means that all structural members of a building or structure has no additional fire rated coating or cover

If you’re having to fill out on a building permit application for a single family residence new construction, the Maximum Allowable Building Height for a Type Five B construction according to Table 503, the answer is, 2 Stories in Floors and 35′ in Building Height and an Allowable Floor Area of 4,800 sq. ft.. I have had some cities say the “Allowable Floor Area” is Air-Conditioned Floor Space, some say it’s “Enclosed” which would be Living Area plus the Garage and the others say it’s the Total Area Under Roof. You will have to check with your own Building Permit Office to see which might apply to you.

Note that all construction types must be classified into the following:
Joisted Masonry
Light Noncombustible
Masonry Noncombustible
Modified Fire Resistive
Fire Resistive

Note that there are two major sources identifying these construction types: International Building Code (IBC) and Insurance Services Office (ISO). ISO is traditionally what insurance companies use to denote type; however, IBC is what Architects and Builders use. The following explains what is expected under both:

International Building Code (IBC): IBC 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 IBC 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 on-going 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.

Insurance Services Office (ISO): The Insurance Services Office, Inc. (ISO) is a provider of data, underwriting, risk management and legal/regulatory services to property-casualty insurers and other clients.

Be aware of both IBC and ISO classification styles. While one company may use ISO classifications, many submission documents may reference IBC classifications and it is important to be able to convert this to an ISO classification. Why is it important to know this? Often a submittal will indicate an IBC type, not an ISO type, and there have been situations where a frame building has been classified as FR because the submittal was read incorrectly!

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)

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