Heavy timber is combustible?
The National Fire Protection Association (NFPA), defines heavy timber construction as a system having main framing members measuring no less than eight inches by eight inches and with exterior walls that are made of a non-combustible material.
Is Heavy timber combustible? I'm reading different books with different definitions of HT construction. Please help.
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Heavy Timber construction is its own Construction Type in the Building Code - Type IV.
Can it burn? Well, yes, it is wood after all. So, yes it's technically "combustible," but the Building Code classifies it differently than just your regular wood construction building (i.e. Type V)
The size and density of the timber members are such that they have been tested to withstand much longer burn and fire spread times, equivalent to that of fire-rated steel columns and other members.
It's thus not really fair to call this "combustible construction," and this is exactly why it has its own Construction Type in the Building Code. If you go to Chapter 6, there's a description of minimum member sizes that you must have in order to meet Type IV requirements.
This is also why a Type IV building can be built bigger and taller than a Type V building.
I'd say don't get confused here - there's no need for you to define heavy timber construction as "combustible" or "non-combustible." It's its own construction type altogether.
Hope that helps.
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Kawai,
I guess I would offer to you this: the exam would never ask you that question. It's too vague - there's gray area in the response. The ARE is not going to pose a code question like this unless the answer is clear, cut and dry, and definitively has a correct answer based on the verbiage in the code. I don't have the code book here in front of me but unless IBC specifically says that Type IV is "combustible" or "non-combustible," then you and I are not able to make that determination and therefore neither is NCARB, and therefore they won't ask you that question. Trust me on this.
If you're getting this question from a review manual you're using, I'm here to tell you to take the question with a grain of salt and move on.
I have taken all of the tests and did not encounter any code questions that were not clearly able to be answered from the code verbiage itself.
Hope that helps.
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If you get a question on the ARE asking what types of construction are non-combustible, the correct answer is Type I and Type II.
Technically Type IV, Heavy Timber, is combustible even though it intrinsically has 2hr rated ext walls and 1hr for the frame. It behaves like it's a protected construction.
Type A are always Protected (more fire-resistant) than B types.
Hope this helps!
Rebekka O'Melia, B.Arch, M. Ed, Registered Architect, NCARB, Step Up ARE Coaching
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I disagree with you there David.
Kawai, read IBC 703 and look at Building Codes Illustrated by Ching, page 101.
"Combustible Materials: The elements of Types III, IV, and V construction allow the use of combustible materials in varying degrees. Additional levels of fire protection can increase the fire-resistance rating of these three types of construction. Note that construction types with mixed elements of noncombustible and combustible construction are considered combustible and are of Types III, IV, or V."
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