Code users should realize that these spandrel wall requirements
are applicable based on the windows in the exterior wall and are
independent of whether the floor or exterior wall is fire-resistance-
rated. The code requirements in Sections 715.4 and 715.5 reference
back to Section 705.8.5 and, as Section 715.5 states, “the
requirements of Section 715.4 shall still apply to the intersection
between the spandrel wall and the floor” even where Section 705.8.5
does not require the spandrel to be rated. Therefore, while Section
705.8.5 may not require a rated spandrel panel or horizontal flame
barrier to prevent the exterior spread of fire to an upper level, the
code will still require the interior void between the curtain wall and
floor to comply with the requirements of Section 715.4. Again, Figure
5.3 shows the difference between the two paths and why the code
mandates following Section 715.4 even where Section 705.8.5 does
not require a rated spandrel wall.
MOVEMENT RATING:
It has also been noted that there are confusions about the significance
of movement consideration in firestop design for curtain wall.
Under normal service conditions, the perimeter joint protection
reacts to both horizontal and vertical movement. The magnitude of
the perimeter joint protection’s movement is dependent upon many
factors. “There are three movements to be considered: vertical,
lateral in the plane of a wall, and lateral normal to a wall plane. The
movements are typically defined by the span ratio; therefore, the
extension of structural spans recently seen in modern structures
significantly increased the deflection building components must
accommodate.” (Kazmierczak, 2010)
“The primary functions of the perimeter joint protection are to
accommodate various movements, such as those induced by
thermal differentials, seismicity, and wind loads, and impede the
vertical spread of fire at the building’s exterior perimeter from the
floor of origin to the floor(s) above.” (Nicholas, 2005).
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