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Do You Know Your Construction Classes? Construction Class 2: Joisted Masonry

July 22, 2013

When I first became a Field Rep at WSRB, the Senior Field Rep in charge of training me had a few words of wisdom to pass down: most importantly, he said, “Know Construction Class 2 (CC 2).  You’re going to use it.”  And he was right.  I don’t have any numbers to back it up, but I would guess that Joisted Masonry construction (Construction Class 2) is the most common for commercial buildings in Washington.  A large portion of the buildings we inspect seem to be CC 2, and it’s easy to see why.

Hollow concrete block buildings are relatively quick and inexpensive to build, more fire-resistive than wood, durable, and easy to maintain. Not all CC 2 buildings are made of hollow blocks or concrete, however.  While less common, a metal frame building with a combustible roof can be rated as Construction Class 2.

“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.

Exterior Walls:

–          Any type or thickness of load-bearing masonry (including hollow concrete blocks, hollow tile, tilt-up concrete, concrete, etc.)

–          Structural, horizontal, and vertical load-bearing unprotected metal supports (rated as noncombustible)

–          Metal siding or non-load-bearing masonry panels supported by metal frame (rated as noncombustible)

Most Joisted Masonry buildings are fairly easy to recognize from the outside.  They range anywhere from small mini-marts to giant warehouses.  Many office buildings are also Joisted Masonry construction.

Joisted Masonry Building

The above picture is a standard-looking office building that would be rated CC 2 due to its combustible roof.

construction class 2 building

From the outside, the picture shown above appears to be a basic tilt-up concrete warehouse.  And it is.  The roofing on the inside is what will cause it to be classified as Joisted Masonry.

construction class 2 building

As you can see here, the roof is a wood deck supported by wood and metal tube trusses on wood columns (not shown here).

Floor and Roof:

–          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 assembly supported by combustible load-bearing construction

–          Metal roof deck with combustible sheathing (wood sheathing, for example) supported by a metal frame

Construction Class 2 building

In this building, we see wood decking under the roof on glue-laminated beams, being supported by metal posts.  The wood decking and wooden beams will cause this building to be a CC 2 even though the posts holding up the roof are metal and the walls are incombustible.

These rules apply to buildings that are more than 33 1/3% this construction type, so long as no other portion of the building is 33 1/3% or more of a more combustible construction class (in this instance, Construction Class 1 – frame).  As always, if you are ever in doubt or have any questions, we’re here to help! Basic WSRB inspections are of no cost to our subscribers and include construction information.  While we’re out there, we can also do a General Casualty Inspection for an additional $75!

Next week, we’ll take a look at Construction Class 3, Noncombustible.

Learn about other construction classes.

Article by: Kristen Skinner

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