Mock Exam Question about construction type

Here is the question:
You are on site reviewing an addition project and are trying to determine the construction type of the existing building. During your inspection, you find that the exterior walls are 8" CMU and the roof is wood trusses.

What construction type is this?

The choices are:

The answer is type VB.
Can someone explain why this is not a type IIIA?


Hi @coachlizschneider do you mind answering this question?

Good Question!
First, let’s review the different construction types listed above.

IIIA - Exterior walls are of noncombustible materials and the interior building elements are of any material permitted by code

IB - Fire resistive, noncombustible materials, except as permitted by Section 603 or elsewhere in the code

VB - Structural elements, exterior walls, and interior walls are of any material permitted by code

IIA - Noncombustible materials, except as permitted by Section 603 or elsewhere in the code

Right away you can rule out I and II because wood framing is combustible. This leaves you with III and V. Typically type III is considered your ordinary construction with masonry walls and a wood roof or floor assembly. Typically VB is reserved for single family home construction and is often all wood framed.

So in this case I would select IIIA. If however, the question stated that the wooden trusses at the roof were not a part of a rated assembly, I would then choose VB because it is the least strict of the options.

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At first you may be tempted to chose III-A because walls are non-combustible and they can achieve a 2hr fire rating at 8" of CMU thk. But, check out the roof! It is not protected, or at least they don’t claim it is, so because we don’t know, then the answer is VB. BTW, a bldg. is Type III-A if it has non-comb walls and flooring and roofing has been treated to achieve at least 1 hr fire-resistance rating.