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The Basics on Construction Classes – Part Two, Joisted Masonry

Posted by Robert Lacy on August 22, 2017

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Construction Class 2, Joisted Masonry (CC 2) is the most common class for commercial buildings in Washington state. You’ll encounter it frequently, so it’s important to recognize it. In this, part two of our series on the Basics of Construction Classifications, we review the joisted masonry class so you can easily spot it.

The Commercial Lines Manual (CLM), Rule 15, defines the joisted masonry class as:

“Buildings where the exterior walls are constructed of masonry materials such as adobe, brick, concrete, gypsum block, hollow concrete block, stone, tile or similar materials and where the floors and roof are combustible (disregarding floors resting directly on the ground).” Rule 15.B.2.

Many associate CC 2 with hollow concrete block buildings, which are relatively fast and inexpensive to construct. They are also more durable and fire-resistant than wood, and easy to maintain. But not all CC 2s are hollow block. The construction of exterior walls also comes into play.

 

Characteristics of exterior walls in the joisted masonry class:

  • Any type or thickness of load-bearing masonry, including hollow concrete blocks, hollow tile, tilt-up concrete, etc.
  • Structural, horizontal and vertical load-bearing unprotected metal supports rated as non-combustible
  • Non-combustible-rated metal siding or non-load-bearing masonry panels supported by metal frame

 

Joisted masonry buildings can feature a variety of floor and roof constructions:

  • The ground floor is disregarded, thus the flooring can be any material, including concrete, wood, asphalt, cement, etc.
  • The roof can be any material on a wood deck.
  • Any roof assemble supported by combustible load-bearing construction.
  • Metal roof deck with combustible sheathing (e.g., wood sheathing) supported by a metal frame.

Most CC 2 buildings are easy to recognize from the outside. They come in all sizes — from small convenience stores to giant warehouses. Joisted masonry construction is also common in office buildings and habitational dwellings. Like CC 1 Frame construction, there is a four-story maximum for joisted masonry buildings.

The standard-looking office building below is designated CC 2, due to its combustible roof.

 

 Construction Pt 2 Joisted Masonry 1.jpg

 

These rules apply to buildings that are more than 33 1/3% CC 2 construction type, as long as no other portion of the building is 33 1/3% or more of a more combustible construction class.

Though it’s less common, buildings with a metal frame and combustible roof may also be rated CC 2.

 

Construction Pt 2 Joisted Masonry 2.jpg

 

The above image shows a building with wood decking on glue-laminated beams, supported by metal posts. The wood decking and beams classify this building as a CC 2, even though the interior posts holding the beams are metal. 

 

Related:

The Basics on Construction Classes Frame

 

If you are ever in doubt or have questions about construction type, we’re here to help. And don’t forget: our basic inspection services are always included in your subscription. For help or information on how to become a Subscriber, Contact Us.

 

Read the next post in our series, where we cover Construction Class 3, Non-Combustible.

 

Robert Lacy, WSRB's Vice President, Inspection Services & Professional Development, oversees our team of commercial property analysts as they produce advisory loss costs, commercial property reports and evaluate automatic fire sprinkler systems. He is involved in the annual evaluation of our loss cost levels and ensuring we are current on coding and rating issues for commercial property.  He also works to encourage continual professional development for all WSRB employees.

Topics: Building Construction, Construction Classes