An input labelled Gypsum underlay in the Wall Input view allows you to choose from None, ½”, 5/8” gypsum underlay. It is available only if the sheathing material selected is Structural I, Structural sheathing or Plywood.
Material Selections
The program implements the panel sheathing and fastener choices in SDPWS Table 4.3B, for a layer of gypsum wallboard or gypsum sheathing board under wood structural panels. It is a more l
Shear Resistance
When there is gypsum underlay, the program gets the shear resistance values from Table 4.3B rather than Table 4.3A. These values do not depend on the choice of ½” or 5/8” gypsum. These are a subset of the values that appear in Table 4.3A, but different combinatons of sheathing and nailing selections yield these capacities.
Table 4.3B Notes
Table 4.3A Notes not Included in 4.3B
The following Table 4A notes do not have an equivalent in Table 4.3B.
Nail Withdrawal Design for Wind C&C Loads
The increased distance that the fastener must pass through the sheathing before it penetrates the framing materials is taken into account when determining withdrawal resistance using NDS Eqn. 11.2.3.
Sheathing Materials Output
In the Sheathing Materials table, the thickness of gypsum is output in a column headed GU after the thickness of the main panel in the shear wall table. The legend explains that GU means gypsum underlay. A dash appears if there is no underlay.
Notes to Shear Results Table
The note regarding specific gravity adjustment is not changed to refer to Table 4.3B note 2 instead of Table 4.3A note 1, because it is possible to have a mixture of walls with and without underlay on the same building.
Note 2 from Table 4.2A is not relevant to walls with gypsum underlay as 7/16 and 15/32 sheathing always have the same shear resistance, so is not included in Table 4.3B. It is not output under the Sheathing Materials table for gypsum underlay.