Protection of Combustible projections

2007 CBC Applies. How would you folks interpret CBC 704.2.3? For an R3 Type VB building I would require that the combustible projections in the area of required protection (into areas with no opening allowed) be 1hr rated at the eave/projection location. It appears to me that the exception noted for this section would clarify the allowable type of construction for the projections of a specific use but would not eleiminate the requirements for protection at these locations.
Any feed back on this topic would be appreciated.
Original Post
Where projections are from walls that are in close proximity to a lot line, they create problems that are due to trapping the convected heat from a fire in an adjacent building. As this trapped heat increases the hazard for the building under consideration, the code describes the location of an imaginary vertical plane beyond which any projection may not extend.

The rule established by the code is that exterior wall projections may not project beyond a point one-third the distance from an assumed vertical plane located where protected openings are required nor more than 12 inches (305 mm) into areas where openings are prohibited. The distance determined from these two methods provides the lesser projection that is to be used.

In order to determine the permitted extent of a projection, we must first evaluate the criteria. The assumed vertical plane at which openings are required to be protected varies, based upon the presence of an automatic sprinkler system. Where the building is not fully sprinklered, that point is first located at 5 feet from the lot line. Table 704.8 indicates that unprotected openings are not permitted in an exterior wall located 5 feet or closer to the lot line. In a fully sprinklered building, the point of determination occurs at 3 feet from the lot line, based on Section 704.8.1.

Figure 1 illustrates the rule for a nonsprinklered building having the exterior wall 6 feet from the lot line. Drawing "A" represents the first criteria while Drawing "B" illustrates the second. The lesser projection of 2 feet would be as shown in Drawing "B".

Projections from buildings are further regulated in order to prevent a fire hazard from inappropriate use of combustible materials attached to exterior walls.

For buildings that the code considers to be of combustible construction (Type III, IV or V construction), both combustible and noncombustible materials are permitted. Where combustible projections are utilized and they extend into an area where openings are either not permitted or where they are required to be protected, the code requires that they be of at least 1-hour fire-resistance-rated construction, of heavy-timber construction, constructed of fire-retardant-treated wood, or as required in Section 1406.3 for balconies and similar projections.

This requirement is based on a potential for a severe exposure hazard and, consequently, the code intends that combustible materials be protected or, alternatively, be of heavy-timber construction, which has comparable performance when exposed to fire. An example is shown in Figure 3, based on the same conclusions established when determining the maximum extent of the projection.


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Thanks for your reply. The information provided is in line with my understanding of the noted topic. I guess my specific comment would be related to the exception of this section in the 2007 CBC which states that an R3 may be Type V construction. I would not interpret this to remove the 1hr protection requirements of the section but I can see others attempting to use this as such.
Thanks for the feed back.
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