A Wood-Frame "Fire Wall" Between an Apartment Building and a Garage
Two wood-frame Type V-B buildings are proposed on one lot: a 12,000-square-foot Group R-2 apartment building and a 6,000-square-foot Group S-2 parking garage. To keep each building within its allowable area, the designer proposes a 2-hour "fire wall" on the common line. The wall is wood-frame, sheathed with two layers of 5/8-inch Type X gypsum on each side, supported by the apartment building's floor framing on one side, and stops at the underside of the roof sheathing. Each side has a 20-minute fire door. The designer cites the 2-hour rating and says the two structures are therefore separate buildings. The code official must review the separation.
1. May the proposed wall function as a fire wall? Explain the structural and continuity requirements.
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Probably not. A fire wall is not merely a wall with a 2-hour rating. It must have independent structural stability so that a fire on one side can cause collapse on that side without pulling down the wall or the building on the other side.
The proposed wall fails several fire-wall requirements:
- Support: It is supported by the apartment building's floor framing on one side. That creates a collapse dependency; a fire in the apartment building could take the wall down with it.
- Continuity: It stops at the underside of the roof sheathing rather than extending above the roof as required for a fire wall.
- Construction: Fire walls are generally required to be of approved noncombustible materials; a wood-frame wall would need a specific approved basis.
A 2-hour rated wall that does not satisfy the fire-wall structural and continuity provisions is a fire barrier, not a fire wall. It does not create two separate buildings.
2. If the wall cannot be a fire wall, what is the effect on the project, and what alternatives exist?
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If the wall is not a fire wall, the R-2 and S-2 occupancies are in one building. The designer must then satisfy the code as a single building:
- Check height and area for the combined building and the applicable construction type.
- Use the occupancy-separation provisions for mixed occupancies, either separated or nonseparated, as applicable.
- Account for the parking garage as part of the same building, including fire separation and ventilation requirements.
Alternatives include:
- Build a compliant fire wall with independent structural stability and the required extension above the roof.
- Reduce the building area or add sprinklers so the single-building area is acceptable.
- Provide the required occupancy separation and treat the building as a mixed-occupancy building.
The official should not accept the label "fire wall" without the structural and continuity features.
3. Evaluate the 20-minute fire doors in the proposed separation.
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The doors are inadequate. Opening protectives must be rated for the assembly in which they occur. A 2-hour fire barrier or fire wall requires a fire-protection-rated door assembly substantially greater than 20 minutes; for a 2-hour assembly, the door rating is typically on the order of 1-1/2 hours, and fire walls impose additional limits on the size and arrangement of openings.
A 20-minute door is appropriate for limited applications such as some corridor doors, not for a 2-hour separation between an apartment building and a parking garage. The official should require doors, frames, hardware, and glazing rated for the actual assembly, with self-closing and latching features, and should verify that the openings are within the limits allowed for the wall type.