NEC Annex E provides a detailed classification of building construction types based on their fire resistance ratings. This informative annex is derived from the NFPA 5000, Building Construction and Safety Code, and offers valuable guidelines for understanding how different types of construction affect the safety and performance of electrical installations.

1. Purpose

Annex E is designed to assist in identifying and understanding the various types of construction as they relate to fire resistance and safety. This classification helps in determining the appropriate electrical installations and protections required for different building types.

2. Types of Construction

The annex categorizes construction types using a system that includes both Roman numerals and Arabic numbers to specify the fire resistance ratings of different structural elements. Here are the main construction types:

• Type I: Fire-resistive construction where all structural elements are noncombustible.
• Type II: Noncombustible construction with a lower fire resistance rating compared to Type I.
• Type III: Exterior walls are noncombustible, but interior structural elements can be of any material permitted by the code.
• Type IV: Heavy timber construction where the structural elements are of large dimensions.
• Type V: Construction where both the exterior and interior structural elements can be of any material permitted by the code, including combustible materials.

3. Fire Resistance Ratings

Each construction type is further broken down based on the fire resistance ratings of its structural components, which include:

• Exterior Bearing Walls
• Interior Bearing Walls
• Columns
• Beams, Girders, Trusses, and Arches
• Floor/Ceiling Assemblies
• Roof/Ceiling Assemblies

These ratings are essential for determining the necessary fire protection measures and for ensuring the overall safety of the building’s electrical systems.

4. Maximum Number of Stories

Annex E includes tables that specify the maximum number of stories allowed for each type of construction, both with and without sprinkler systems. For example:

• Type V Non-rated: 2 stories
• Type V Non-rated, Sprinklered: 3 stories
• Type IV Heavy Timber: 4 stories
• Type IV Heavy Timber, Sprinklered: 5 stories

5. Cross-Reference of Building Codes

The annex also provides a cross-reference of building construction types according to various model building codes, such as the Uniform Building Code (UBC), National Building Code (NBC), Standard Building Code (SBC), and International Building Code (IBC). This helps ensure consistency and compliance across different regulatory frameworks.

For further details and specific guidelines, it is recommended to consult the NEC Handbook and additional resources provided by the NFPA. Further insights can be found on SunCam and The NEC Wiki.