Roof Framing Considerations on Type IIIA Projects
Why “Non-Bearing” Exterior Walls Are Often Bearing in Disguise
Type IIIA construction brings a unique set of challenges—especially at the roof level. One issue we continue to see on mid-rise, wood-frame projects is the assumption that exterior walls can be treated as non-bearing through strategic roof framing alone. In practice, that assumption often doesn’t hold up once full gravity and lateral loads are accounted for.
This post breaks down the issue, explains why common framing workarounds may fall short, and outlines two realistic paths forward.
The Core Requirement: 2-Hour Exterior Walls
Under Type IIIA construction, exterior bearing walls are required to have a 2-hour fire-resistance rating. Achieving this typically means adding an additional layer of 5/8” Type X gypsum sheathing on the interior face of the wall.
Because this impacts cost, detailing, and coordination, design teams often look for ways to classify exterior walls as non-bearing—allowing for lighter wall assemblies and simpler detailing.
The Common Workaround: Girder Trusses Pulled Inboard
Historically, a frequent strategy has been to modify roof truss layouts so that girder trusses are positioned close to—but not directly over—the exterior wall. The idea is simple:
- Reduce direct roof load on the exterior wall
- Keep wall loads under the non-bearing threshold (commonly cited as <100 plf, excluding self-weight)
- Avoid triggering 2-hour bearing wall requirements
In framing plans, this often shows up as interior girders (sometimes highlighted in red), with jack trusses spanning to them rather than bearing directly on the exterior wall.
At first glance, this looks like a clean solution.
Where the Strategy Breaks Down
The problem is that simple gravity load checks are not the full story.
While pulling girders inboard may reduce tributary dead load, it does not sufficiently reduce total design gravity load once you account for:
- Wind uplift and downward pressure
- Load combinations required by the structural code
- Concentrated reactions at truss bearings
In one recent project, a jack truss showed a gravity reaction of 1,277 lbs at the exterior wall. Even dividing this by two (assuming 24” o.c. trusses), the resulting load far exceeds the non-bearing wall definition.
In other words:
The wall may look non-bearing on plan, but structurally, it is not.
As a result, the exterior wall still qualifies as bearing and must be detailed as a 2-hour-rated assembly—negating the original intent of the framing workaround.
Why This Matters
If this issue isn’t resolved early, it can lead to:
- Late-stage framing redesign
- Unexpected 2HR wall requirements during permitting
- Cost increases due to added gypsum, detailing, and inspections
- Conflicts between architectural, structural, and truss engineering documents
This is especially common on podium + wood or wrap-style Type IIIA buildings where roof geometry and lateral systems are already complex.
Two Realistic Paths Forward
Once the full structural loading is understood, there are really two viable options:
Option 1: True Load Isolation via Balloon or Semi-Balloon Framing
Detail the exterior wall so that roof loads bypass it entirely. This typically means:
- Balloon or semi-balloon framing at the top level
- Continuous load paths that transfer roof loads directly to interior bearing elements
- Careful detailing at floor lines to avoid unintended load transfer
This approach can work—but it requires intentional detailing and close coordination with the structural engineer and truss designer.
Option 2: Accept Bearing Walls and Design Accordingly
The simpler—and often safer—option is to:
- Acknowledge the exterior wall as bearing
- Provide 2-hour-rated wall assemblies
- Allow roof trusses to bear directly on the exterior wall with a straightforward framing layout
While this may increase wall assembly cost, it often reduces risk, redesign, and coordination effort.
Key Takeaway
In Type IIIA projects, you can’t frame your way out of fire ratings without a full load-path analysis. What appears non-bearing on plan may still be bearing once real-world forces are applied.
The best outcomes happen when:
- Fire rating implications are discussed early
- Structural load paths are clearly understood
- The team chooses clarity over complexity
Sometimes the “simpler” framing solution is actually the most economical one.