Masonry Magazine May 2010 Page. 22
CONNECTORS, ANCHORS AND FASTENERS
and fastening to 16-gauge stud, will require a MINIMUM screw length of:
* .06+.056+.625+.188+.203+.125 = 1.257 inch, or 1-1/2 inch
Using a #12 or 1/4-inch screw for the same conditions, the minimum length should be:
* .06+.056+.625+.250+.500+.125 = 1.616 inch, or 1-5/8 inch
It is important to incorporate a sealant washer as a means to restrict moisture and air flow through the connection.
Conservatively, a 2-inch minimum length screw is appropriate for all the combinations. Piercing leg or single pole type tie bases require longer screws predicated on the insulation thickness and the type of base plate.
Screw head type
A HEX WASHER HEAD (HWD) screw (usually 5/16-inch hex) is the preferred style. It is efficient to drive and its profile is relatively low. Pan head and Flat head styles are also available but more tedious to install and the aesthetic value is not warranted. It is important to incorporate a sealant washer as a means to restrict moisture and air flow through the connection. It also provides a material separation in the event a stainless steel base plate is used. This would avoid a galvanic reaction due to the differential materials.
Screw performance
THE STEEL STUD Manufacturer's Association publishes a conservative allowable fastener performance in 16 gauge stud as 137 pounds and 156 pounds tension per screw for the #10 and #12, respectively (without reference to drill point effects). The individual manufacturer's pull-out data for the selected screw sizes is a more realistic approach for capacity consideration. For example, allowable tension loads varied from 200 pounds to 800 pounds from seven different manufacturers. Selecting the screw to use is based on the performance expectations and the quantity per tie required by the tie manufacture. Single fastener designed ties are cost efficient, and quick research regarding the screw performance will provide the appropriate strength for the connection and less breaches in the air barrier. Based on the live load determined above, the resulting force of 56 pounds tension and compression would produce a safety factor of 2.5:1 and 2.8:1 for the screw sizes listed by the SSMA. If a seismic condition exists, the live load can be 70 pounds or greater and the resulting safety factor can be 2:1 or 2.2:1.