2 HR Rated wall assembly

[righter101]

Referring to the GA-600-2006 Fire resistance design manual, specifically the generic 2 hour wall assembly "WP9206" which requires 4 layers of 5/8" type X gyp, staggered joints, specific screw spacing....

On the 3rd layer, there is a requirement for 1 7/8" screws at 12" o/c which would get it just through the layers below. Then there is a requirement over the 3rd layer for 1.5" wide steel straps at all vertical joints and intermediate channels (below the base layer) with 2 5/8" screws at 12" o/c

Here is the question:

Since there is no mention of spacing or staggering of the screws for the board its self, with respect to the screws for the straps, is it necessary to install the 12" o/c ones holding the drywall, as it would be duplicated by the screws holding the straps....

I am leaning towards, yes, it should be done exaclty as described, but wondering if anyone has any insight as to why. the gyp manual offers no explanation.

Thoughts??

 

[Examiner]

http://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/showpage.html?name=BXUV.V421&ccnshorttitle=Fire+Resistance+Ratings+-+ANSI/UL+263&objid=1074331425&cfgid=1073741824&version=versionless&parent_id=1073984818&sequence=1

Link to UL V421 on the UL site. Internet search for WP9206 came up with UL V421 as the item. You may have to contact UL or the Gyp Assoc for input. http://www.gypsum.org/download.html

 

[Sandman]

Nope. The FACE layer must be fastened to the steel straps with 1" Type S drywall screws 8" o.c. as specified. Think of the steel straps as a secondary means of attachment and support. The first three layers and the steel straps are attached to the rigid furring channels with type S screws of increasing length and the last layer is attached to the steel straps with 1" screws.

The assembly was tested per ASTM E 119 as specified so if any changes are made in the field, it would be difficult to argue the 2 hour fire-resistance is not compromised without testing the modified installation.

GA FILE NO. WP 9206 GENERIC 2 HOUR

Thickness: Varies

Approx. Weight: 9.5 psf

Fire Test: UL R7406, R4024;

96NK36592; 8-23-99;

UL Design V421

GYPSUM WALLBOARD, RIGID FURRING CHANNELS,

STEEL GIRTS, STEEL WALL PANELS

EXTERIOR SIDE: Minimum 26 gage steel exterior wall panels applied at right angles to

horizontal, 6" to 12" deep, “Z” or “C” shaped, 0.056" to 0.120" thick steel girts 48" o.c. with 1-1/2" long, No. 12-14 self-drilling screws 12" o.c.

INTERIOR SIDE: Base layer 5/8" type X gypsum wallboard applied parallel or at right

angles to rigid furring channels 24" o.c. with 1" Type S drywall screws 24" o.c. Furring

channels attached at right angles to girts with two 3/8" long, Type S-12 panhead screws at each girt. Second layer 5/8" type X gypsum wallboard applied parallel or at right angles to channels with 1-5/8" Type S drywall screws 12" o.c. Joints offset 24" from base layer joints. Third layer 5/8" type X gypsum wallboard applied parallel or at right angles to channels with 1-7/8" Type S drywall screws 12" o.c. Joints offset 24" from second layer joints. Steel straps, 0.020" x 1-1/2" wide, vertically applied over third layer at vertical joints and intermediate channels with 2-5/8" Type S drywall screws 12" o.c. Face layer 5/8" type X gypsum wallboard applied parallel or at right angles to steel straps with 1" Type S drywall screws 8" o.c. Joints offset 24" from third layer joints. (LOAD-BEARING)

 

[righter101]

Thanks for the feedback and links.