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Do You Know Your Construction Classes? Construction Class 1: Frame

July 15, 2013

Construction classes: a frequently mentioned piece of information on our inspection requests, and one that we’re often asked to interpret.  So, over the next few weeks, I’ll spend some time explaining the WSRB Construction Classifications (CC).

Construction classes are outlined in the Commercial Lines Manual, Rule 15—the final say when determining a construction class.

A few things to keep in mind:

–          Without experience (and even with!) it’s difficult to distinguish between construction classes, 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 are not considered when determining Construction Class.

All of this is what makes an experienced Field Representative’s inspection and report so vitally important.  The following will hopefully give a good explanation and a few visuals to help understand the basics of construction classes.

This applies to buildings that are more than 33 1/3% frame construction.  And remember, if you’re ever confused or have a building that you’re unsure of, we’re always here to help! Our inspections are of no cost to WSRB subscribers.

Construction Class 1: Frame

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

This is the most basic and one of the more commonly seen construction types in Washington.  The above explanation sounds simple enough, and it is.


–          A building with exterior walls of any combustible material (such as vinyl, wood siding, tarp or cloth, etc.) which are supported by a wood frame would be considered a CC 1 building.

–          The siding of the building can also be a less combustible material—metal sheathing or brick veneer for instance—and still be considered CC 1 as long as the supporting members are made of wood frame.

–          Metal framing and a metal roof with combustible sheathing (wood paneling along the walls) or combustible insulation can also make a building CC 1.

What might this look like?  During the construction process, it might look like this:

Frame Construction

As you can see, the supports of the building are wood, as well as the exterior wall panels.

Frame construction

This building has metal siding, but upon closer inspection, the wood frame around the door is visible.  This in itself doesn’t necessarily make a building frame, but the wood framing pictured also extends to support the metal siding and metal roof of the building.  There are wood columns throughout the building to help support the roof.

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 would also be CC 1 if the roof were held up by any load-bearing combustible supports.

  • For example, a commonly seen frame roof construction consists of metal decking on metal trusses on wood beams supported by wood columns.

Construction Class 1 is the most combustible and frequently used in habitational buildings as well as smaller retail/repair-type shops and older buildings.  Generally, it is less expensive to construct, holds up well over time, and is lighter weight (compared to other construction types), possibly making it safer in an earthquake.  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, as properly maintained sprinkler systems in this type of construction can be a major insurance benefit!

In our next article, we’ll look at Construction Class 2: Joisted Masonry.

Article by: Kristen Skinner

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