Spatial separation is a term used to describe a set of construction design principles that reduce the risk of the spread of fire from one building or fire compartment to another building, fire compartment or property through heat radiation. The concept of unprotected openings assumes an important role in spatial separation design, by way of minimizing potential excessive heat radiation through unprotected assemblies or components.
Let’s Define the Term: Unprotected Opening
Consider the term unprotected opening, I bet a few things come to mind; windows, doors, and other physical openings such as mechanical openings. Did you know the term unprotected opening also applies to any portion of a wall that achieves a fire-resistance rating less than that required for the exposing building face?
“Unprotected Opening means a doorway, window or another opening other than one equipped with a closure having the required fire-protection rating or any portion of a wall forming part of the exposing building face that has a fire-resistance rating less than that required for the exposing building face.”
The definition says “any portion of the wall”, do they mean “any”? Consider a vertical steel building column, or a built-up wood column, or perhaps a certain percentage of a lower or upper portion of a wood stud wall? Can a structural member that maintains the vertical orientation of the exposing building face be considered as an unprotected opening?
According to the definition, “any portion of a wall” could be considered as an unprotected opening. As a building official, I have reviewed many creative attempts to justify the omission of a required fire-resistance rating for structural members that keep exposing building faces vertical and intact. Under certain conditions, this may not be an unreasonable approach, but as the limiting decreases or the occupancy hazard increases, the threat of premature collapse of the exposing building face also increases.
Intent and Consistency
To fully understand the intent and consistency of the application of a code provision, I often engage in a thought exercise that creates an exaggerated situation that is acceptable by the provisions and determine if I have the same opinion as the situation that was not exaggerated.
For example, consider an F1 major occupancy, single storey in building height, not exceeding 800 m2 and unsprinklered. The limiting distance permits a maximum area of unprotected opening of 25%, requires a 2 hour fire-resistance rating, combustible or noncombustible construction and noncombustible cladding. As this building and its exposing building face are permitted to be constructed out of combustible construction, the designer chooses a pole building design consisting of built-up 6 x 6 wood columns.
Could the designer leave each column exposed to the interior of the building and consider this unprotected vertical wood column as an unprotected opening? As another example, the designer proposes a wood stud wall constructed out of 2 x 6 wood studs. Could the designer choose to leave the bottom 25% of the entire wall assembly unrated and exposed to the interior of the building and consider this exposed portion of a wood stud wall as an unprotected opening?
Do you think the “conforming” assemblies above would remain intact and perform their intended function for the duration required by the code? This design would likely lead to the premature collapse of the exposing building face during a fire event, and as a building official, I am in a challenging situation where on one hand I understand the grammar of the defined term, and on the other, I see a design that does not function as a compliant solution.
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So, I Submitted a Code Change Request
I have been challenged on many occasions by this issue so I decided to submit a code change request to the Canadian Commission on Building and Fire Codes. In this code change request, I expressed concern with the use of the phrase “any portion of a wall”, and offered a new solution to this problem. It is my opinion, that the applicable provisions intend to reduce the risk of fire spread through heat radiation and reduce the risk of premature failure of the exposing building in the time necessary for the fire department to perform their duties. As a result I requested to modify the definition as follows:
“Unprotected Opening means a doorway, window or other opening other than one equipped with a closure having the required fire-protection rating, or any portion of a wall forming part of the exposing building face that has a fire-resistance rating less than that required for the exposing building face, but does not include an integral structural member that maintains the vertical orientation of the exposing building face.”
This amendment would clarify that a portion of a wall can be considered as an unprotected opening, provided that the portion of the wall is designed so that if it is an unprotected opening and is exposed to fire, that the failure of the unprotected opening does not cause the failure of the exposing building face. As an example, a designer could design a framed opening, typical of a window or door, but instead of installing a window or door, the designer chooses to install a wall with a fire-resistance rating less than that required for the exposing building face. In this design, failure of the wall with the lesser fire-resistance rating could collapse, but the framed opening combined with encapsulation and segregation would protect the remainder of the exposing building face as all integral structural members would achieve the fire-resistance rating required for the wall.
Have you ever encountered construction where a structural component of an exposing building face was considered to be an unprotected opening?
