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The Basics on Construction Classes – Part One, Frame

Posted by Robert Lacy on August 15, 2017

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Improving your understanding of construction classes can help you get the greatest value from WSRB inspections and commercial property reports. To help you do this, we’re running The Basics of Construction Classifications series over the next few months. We’ll review all six construction types, covering the nuances with photos and examples, ensuring you can identify the classes. We'll also cover mixed construction. Be sure to check out all the posts.  

The Commercial Lines Manual, Rule 15 outlines the construction class parameters. While the manual has the final say, determining construction classes is not always clear-cut. It’s helpful to keep a few things in mind:

  • Without experience (and even with it) distinguishing between construction classes is difficult, especially if sheathing or interior construction elements obstruct a full view of the wall and ceiling assemblies. 
  • Multiple construction types within a single building can change the construction class. 
  • Basement walls and areas do not come into consideration when determining construction class.


Because so many factors can impact the construction class, including those that can’t be seen from the outside, an experienced Commercial Property Analyst’s inspection and report is vital to the underwriting and rating process.

Need help with classifying buildings? WSRB is happy to assist you. Our standard inspections are available at no additional cost for our subscribing members. You can request an inspection by logging in to the member portion of our site.


Construction Class (CC) 1 Frame:

Frame is one of the most basic, and common, construction types in Washington. To receive the CC 1 Frame designation, more than 33 1/3% of the construction must be frame.

The CLM defines the Frame construction class as:

"Buildings where the exterior walls are wood or other combustible materials, including construction where combustible materials are combined with other materials (such as brick veneer, stone veneer, wood ironclad, stucco on wood)." CLM, Rule 15.B.1

Let’s review the components for clarity.


Walls and siding:

  • A building with exterior walls of any combustible material (such as vinyl, wood siding, tarp or cloth, etc.) supported by a wood frame would be a CC 1 structure.
  • The siding of the building can also be a less combustible material (like metal sheathing or brick veneer) and still be CC 1, as long as the supporting members are made of wood frame.
  • Framing and a metal roof with combustible insulation or sheathing (e.g., wood paneling along the walls) may also make a building CC 1.

During the construction process, a CC 1 building might look like this:

 construction wood frame

You can see that the supports of the building and the wall panels are wood.

Let’s look at a completed building. The next photo shows a recently inspected hotel featuring classic frame construction.

 construction complex

Now for a tricky classification. The next image depicts a metal building. Upon closer inspection, our Commercial Property Analyst classified this building as CC1, Frame Construction. The main structure is a wood frame that can only be viewed by gaining access to the interior.

 construction blue buildings

Floor and Roof:

  • The ground floor can be of any material, including wood, concrete, asphalt, dirt, etc.
  • The roof can be of any material on a wood decking, including metal, composition shingles, built-up composition, etc.
  • A building is classified as CC 1 if the roof is held up by any load-bearing combustible supports.

Habitational dwellings, small retail shops and older buildings frequently use frame construction.


Advantages and disadvantages to CC 1 construction:

Compared to other construction types, CC 1 buildings are less expensive to construct, hold up well over time and are lighter in weight.

The main disadvantage to CC 1 is that it’s the most combustible construction type. If you have a customer with a CC 1 risk and an automatic sprinkler system, be sure you’ve looked into our No Sprinkler Left Behind program. Properly maintained sprinkler systems in this type of construction can be a major insurance benefit.

I hope this post gave you a broader understanding of Frame construction class (CC 1). If you have any questions or customized inspection needs, please Contact Us.


Read the next post in our series, where we cover Construction Class 2, Joisted Masonry


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