two-hour wood wall assembly help

Feb 8 '06 14 Last Comment
mean prank riverbank
Feb 8, 06 6:16 pm

any of you practitioners out there have knowledge of two-hour wall assemblies using wood studs that use something other than 2 layers of 5/8 gyp on either side?

like is oft' the case i have a two hour wall meeting a one hour wall in the same plane and i'm looking for a way to keep them as close to flush as possible w/o furring out the other wall to match.

book references, web references, ul or wp #s please.



Feb 8, 06 8:00 pm

2-hour wall finished face to face = 5.5":

2″ × 4″ wood studs 16″ on center with metal lath and 7/8″ neat wood-fibered
gypsum plaster each side. Lath attached by 6d common nails, 7″ on center.
Nails driven 11/4″ and bent over.

1-hour wall finished face to face = 5.5"

2″ × 4″ wood studs 16″ on center with two layers 1/2″ regular gypsum wallboarde
applied vertically or horizontally each sidek, joints staggered. Nail base layer
with 5d coolern or wallboardn nails at 8″ on center face layer with 8d coolern or
wallboardn nails at 8″ on center.

Feb 9, 06 9:22 am

As jh:
UL Fire Resistance Directory:
Design No. U301, U334, U350, U357

Chilly Willy
Feb 9, 06 11:26 am

Double up on the 1-hour wall and just make it a 2 hour wall. Shouldn't cost too much more.

Feb 9, 06 3:26 pm

second that

Feb 9, 06 4:28 pm

You cold also stager the studs ( ½”) in the 1hr wall, but labor wise it would be easier just to double up the drywall.

will gallowaywill galloway
Feb 9, 06 5:14 pm

treble the doubling.

Feb 10, 06 9:54 am

as a sidenote about alternate fireproofing, check out shigeru ban's highrise in osaka - plywood was used as fireproofing around the columns

and to support his claim of a 'fireproof' wood, the results from tests show that the wood reached a charcoal state and stopped burning at a certain point. i'm not sure of the specifics, but there is some detailed info in his phaidon monograph.

Chilly Willy
Feb 10, 06 12:52 pm

There are fire-treated plywoods. We did a boathouse below the floodplain and had to use some as a finish material since gyp. bd. & plaster are not allowed. I understand they are made with some nasty chemicals like arsenic and formaldahyde, although I think some eco alternatives have come out in the last few years. What you're talking about sounds like the theory behind heavy timber construction.

Jun 13, 13 1:43 pm

Could someone pass me the UL Design No for a 1 hr exterior wall.  Ideally looking for a 5/8" gyp interior, 2x6 stud and 7/16" OSB exterior; or something close; perhaps need another layer of gyp under the OSB?


Jun 14, 13 1:34 pm

Also look at the GA manual online for gypsum rated assemblies

Jun 14, 13 1:34 pm

And the damn building code.

Jun 14, 13 4:23 pm

Very handy UL assembly search page that I have been using for a number of years.  It has recently be revamped to be a little more user-friendly.

Jun 19, 13 12:37 pm

Thanks for the sites and links.  I appreciate the help.

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