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Understanding Rule 85: Construction Classes

September 2, 2025

This is Part II of our seven-part series on Understanding Rule 85. In this series, we delve into the intricacies of Rule 85 and its implications for property insurance.

In this installment, we will delve into the different construction types, exploring how they are defined, providing examples, and discussing their importance in class ratings.

Construction classes

The construction type of a building plays a crucial role in its class rating, influencing its risk profile and insurance costs. Here, we define and provide examples of the seven primary construction types used in class ratings.

CC-Frame-1

CC 1: Frame

Definition:
Frame construction buildings have exterior walls made of wood or other combustible materials. Includes structures with a combination of combustible materials and other types, such as brick veneer, stone veneer, or stucco on wood.

Examples:

  • Wood-framed houses
  • Small commercial buildings with wood or metal siding
  • Residential structures with wooden supports

Importance in class rating:
Frame construction is common in residential properties due to its cost-effectiveness and ease of construction. It generally carries a higher insurance premium due to increased fire risk.

CC-Joisted Masonry

CC 2: Joisted Masonry

Definition:
Joisted Masonry construction buildings have exterior walls made of masonry materials such as adobe, brick, concrete, gypsum block, stone, or tile, with combustible floors and roofs.

Examples:

  • Commercial buildings with brick/stone exteriors and wooden roofs
  • Apartment complexes with masonry walls
  • Warehouses with reinforced masonry walls
Importance in class rating:

Joisted Masonry offers better fire resistance than Frame construction, potentially resulting in lower insurance premiums. Its balanced use of materials provides moderate protection against fire.

CC-Non-Combustible-1

CC 3: Non-Combustible

Definition:
Non-Combustible construction buildings have exterior walls, floors, and roofs constructed of and supported by metal, asbestos, gypsum, or other non-combustible materials.

Examples:

  • Industrial buildings with steel frames and concrete floors
  • Commercial structures with metal roofs and walls
  • Warehouses with reinforced concrete walls

Importance in class rating:
Non-combustible buildings are more favorable in class ratings, potentially reducing insurance costs due to their enhanced fire protection (often used in industrial and commercial applications where fire risk needs to be minimized).

CC - Masonry Non-Combustible-1

CC 4: Masonry Non-Combustible

Definition:
Masonry Non-Combustible construction buildings have exterior walls constructed of masonry materials, with floors and roofs made of metal or other non-combustible materials.

Examples:

  • Factories with brick walls and steel roofs
  • Schools with concrete block walls and metal flooring
  • Office buildings with stone exteriors and non-combustible interiors

Importance in class rating:
Masonry Non-Combustible buildings combine the durable masonry with fire resistant non-combustible materials, offering a balance of protection and cost-effectiveness.

CC - Modified Fire-Resistive-1

CC 5: Modified Fire-Resistive

Definition:
Modified Fire-Resistive construction buildings have exterior walls, floors, and roofs constructed of masonry or fire-resistive material with a fire-resistance rating of between one and two hours.

Examples:

  • Mid-rise office buildings with reinforced concrete and fireproofing
  • Retail centers with masonry walls and protected steel structures
  • Mixed-use buildings with enhanced fire resistance

Importance in class rating:
Modified Fire-Resistive buildings provide a moderate level of fire protection suitable for many commercial applications; often lead to favorable insurance premiums due to enhanced safety features.

CC - Fire-Resistive-1

CC 6: Fire-Resistive

Definition:
Fire-Resistive construction buildings have exterior walls, floors, and roofs constructed of masonry or fire-resistive materials with a fire-resistance rating of more than two hours. 

Examples:

  • High-rise buildings with reinforced concrete and steel structures
  • Government and institutional buildings with advanced fireproofing
  • Hospitals and medical facilities with fire-resistive materials

Importance in class rating:
Fire-Resistive buildings have the highest level of fire protection, often resulting in the lowest insurance premiums.

CC - Mixed-1

Mixed construction

Definition:
Mixed Construction refers to buildings that incorporate elements from several construction classes. Determining the class rating for mixed construction involves assessing the predominant materials and their fire resistance.

Examples:

  • Buildings with a combination of masonry and steel in various sections
  • Complex structures with different floors having different construction classes
  • Renovated buildings with updated fireproofing and structural materials

Handling mixed construction:
Accurately classifying mixed construction requires a detailed understanding of the building’s design and materials. Insurers may need to consider specific sections individually to determine the overall class rating and insurance premiums.

Importance of construction type in class ratings

Construction type is an important factor for determining a building's class rating, influencing the overall risk assessment and insurance premiums. Here's why:

Risk assessment: Fire-resistant construction types typically have lower risk profiles, leading to more favorable class ratings.

Insurance premiums: Buildings with better fire resistance often qualify for lower premiums.

Compliance and safety: Knowing the construction type helps property owners comply with safety regulations and building codes, reducing legal issues and liabilities. 

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For more information on construction classes, check out WSRB's Basics on Construction Classes.

Up next is Part III of our Understanding Rule 85; explore the impact of occupancy on class ratings and how it affects insurance policies.

Chris Barclay spent 30 years underwriting personal, commercial and agricultural lines in the Western U.S. before joining WSRB to develop innovative, easy-to-use tools that help insurers manage both entire portfolios and individual accounts. Chris lives and works in Spokane, Washington.

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