Section 603 Combustible Materials In Type II Construction

[John DeBruyne]

2015 (!) Michigan Building Code. Type IIB Construction. S-1 Use Group.

Section 603 covers allowable combustible materials in Type II construction. 603.1.1.3 allows fire-retardant treated wood in roof construction. Although italicized, it does not appear that fire-retardant treated wood is defined in the Chapter 2 Definitions.

My question: Is "fire-retardant treated wood" considered "combustible" since it is listed in Section 603? More specifically, I am using this in the context of 718.4 where draftstopping is required in "combustible" attic construction.

 

[steveray]

2015 (!) Michigan Building Code. Type IIB Construction. S-1 Use Group.

Section 603 covers allowable combustible materials in Type II construction. 603.1.1.3 allows fire-retardant treated wood in roof construction. Although italicized, it does not appear that fire-retardant treated wood is defined in the Chapter 2 Definitions.

My question: Is "fire-retardant treated wood" considered "combustible" since it is listed in Section 603? More specifically, I am using this in the context of 718.4 where draftstopping is required in "combustible" attic construction.

It is not non-combustible (E136?)....so it is combustible....that is the rub...So unless it is an NFPA 13 building, you need the draftstopping...

I believe it meets limited combustible from NFPA

 

[RLGA]

Look under “Treated Wood” in Chapter 2.

FRTW is considered combustible; otherwise, they would not have included it in Section 603 which is titled “Combustible Material in Type I and II Construction.”

 

[Yankee Chronicler]

Technically, fire-retardant treated wood is considered "limited combustible" material.

ICC 2021 IBC Commentary to section 802.5:

This section simply points out that this chapter allows
combustible materials as interior finish. This would
include the finish of walls that are required to be “noncombustible”
due to the building’s type of construction
or other code requirements. This is supported by the
provisions of Section 603.1, which allow limited combustible
materials in Types I and II construction. Item 5
of Section 603.1 lists interior floor finish and interior
finish, trim and millwork, such as doors, door frames,
window sashes and frames, as allowable combustible
materials. The majority of materials that are used as
finish materials are combustible in nature. However, all
materials in regulated environments are required to
exhibit maximum flame spread and smoke-developed
indexes or an equivalent performance on heat and
smoke release in an appropriate room-corner fire test.
Section 803 clarifies the limits on such materials by
limiting the flame spread index and smoke-developed
index of such materials in certain portions of the building
based on the occupancy.

This refers to section 603.1. The IBC doesn't have a definition for "limited combustible" and section 603.1 doesn't use the term, so I'm not sure what the point is on using that term in the Commentary, but generically when discussing FRT wood I have always heard it described as "limited combustible."

 

[RLGA]

“Limited-combustible material” is an NFPA-defined term. The Commentary’s use of that term is ICC’s way of introducing it to the ICC world without fully incorporating it into the code. Maybe in the future, it will be added to the ICC codes.

Limited-combustible materials, per NFPA, are anything with a heat value of not more than 3,500 BTU/lb per NFPA 259 plus other limitations per NFPA 2965 and ASTM E84. The IBC references NFPA 259 for plastics but does not reference NFPA 2965.

The I-Codes establish the method of identifying non-combustible materials only (i.e., ASTM E136); everything else is considered combustible. However, certain materials (e.g., gypsum board and FRTW) may be identified as exceptions where permitted. In this case, I prefer the NFPA method, which is more performance-based.

 

[steveray]

Great...Now we all have to pay NFPA $5 for typing limited combustible.....