Fire rating of beam at balcony

[Yikes]

I have an exterior exit balcony on an apartment building (V-A). The balcony structure is one-hour rated (stucco plaster on the bottom of the balcony floor framing, elastomeric coating on top). The outer edge of the balcony is a 7” x 9.5” PSL beam (think of it like a rim joist), and a prefab metal stair is scheduled to attach to it.

Where the stair stringers fasten to side of the PSL (metal plates and bolts), is it OK to omit the stucco wrap? Will it still keep the one hour rating? Is the 7 x 9.5” PSL essentially acting like "heavy timber" in terms of its own fire resistance, such that it does not need the stucco wrap?

On the rest of the apartment unit balconies, the designer would also prefer to finish the exterior vertical face of this PSL "rim joist" with a metal flashing instead of stucco, so the same question applies.

The plans have already been permitted by the building department, I just wanted to clarify before I finalize the stair shop drawings.

 

[Big Mac]

To be considered equivalent to a 6" X 10" solid sawn piece of heavy timber, the manufctured member would need to be not less than 10.5" deep. Table 602.4.

 

[Builder Bob]

That would depend..... I would suggest using the WFM manual chapter 10 or 11 for "calculated fire resistance of wooden members. For example, pine genrally chars at the rate of 1.25 inches per hour...... If you are looking for an hour, the wooden structural member would have to be of sufficent size to carry the loads plus 1.25" for the structural requirement. For example, 4 X 4 beam is required for structural support. To leave the Beam exposed and have a 1 hour fire resistance rating, the beam would have to be upsized to a 6 X 6 beam.

Just food for thought....