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RE: drywall type shearwalls- l

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While the end of Scott's message provides a reasonable solution, what fails
me is the rationale that would allow plywood to be used over Gypsum. Not
only is the shear greatly reduced, I would assume that the requirement is to
protect the structural integrity of the wall from the flame or heat applied
from outside the wall rather than within the wall cavity. What purpose would
there be to providing a flammable material (plywood) over a fire barrier
(Gypsum) only to protect the stud wall within, when the strength of the
system is maintained by applying the plywood directly to the studs and then
protecting the wall assembly from fire by installation of the Gypsum over
the plywood and studs.
I'm confused because the wording of the code seems convoluted at best and I
would question if this was the original intention and what purpose it
serves.

Maybe I have this backward, but I am making this argument from the section
of Scott's message that states:
"The way the UBC is now, for a rated exterior wall you could put plywood
over the
exterior sheetrock as a finish but sheetrock would be required both sides.
IBC 704.5 allows exterior rated wall assemblies, farther than 5 feet from
property lines, to be rated from the inside, if you can find such an
assembly.  This means if you can find an exterior assembly that has plywood
on the outside, that is rated from inside, it is OK."

I don't understand where this would ever be used?

Dennis S. Wish, PE

-----Original Message-----
From: Haan, Scott M. [mailto:HaanSM(--nospam--at)ci.anchorage.ak.us]
Sent: Friday, March 09, 2001 8:40 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: drywall type shearwalls- l


When the "type of construction" indicated in UBC Table 6-A or IBC Table 601
requires wall assemblies to be fire rated then the walls are required to be
tested fire-rated assemblies unless a "fire resistive sprinkler
substitution" is used per UBC 508 or IBC Table 601 footnote d.  Some types
of separation walls are not allowed to use this "fire resistive
substitution".

IBC 704.5 indicates if an exterior wall is less than 5 feet from a property
line then the wall needs to be rated from both sides and if it is farther
than 5' from a property line then the wall can be rated from the inside.
The UBC requires walls to be rated from both sides regardless.  The way the
UBC is now, for a rated exterior wall you could put plywood over the
exterior sheetrock as a finish but sheetrock would be required both sides.
IBC 704.5 allows exterior rated wall assemblies, farther than 5 feet from
property lines, to be rated from the inside, if you can find such an
assembly.  This means if you can find an exterior assembly that has plywood
on the outside, that is rated from inside, it is OK.

UBC Table 7-B footnote 17 and IBC Table 719.1 footnote L indicates: "Wood
structural panels may be installed between the fire protection and the wood
studs on either the interior or the exterior of wood frame assemblies in
this table, provided the length of the fasteners used to attach the fire
protection are increased by an amount at least equal to the thickness of the
wood structural panel."  This means for rated wood stud walls you can put
plywood under the sheetrock.  This exception is for wood stud walls and
unless you find a metal stud wall that meets this exception you should not
place plywood under sheetrock on metal stud walls!!!!!!

Scott M Haan  P.E.
Plan Review Engineer
Building Safety Division http://muni.org/building,
Development Services Department,
Municipality of Anchorage
phone: 907-343-8183   fax: 907-249-7399


> -----Original Message-----
> From:	Mark Gilligan [SMTP:MarkKGilligan(--nospam--at)compuserve.com]
> Sent:	Friday, March 09, 2001 6:41 AM
> To:	INTERNET:seaint(--nospam--at)seaint.org
> Subject:	Re: drywall  type shearwalls-  l
>
> What is not clear is why does the fire rating prevent the use of plywood
> sheathing.  In California it is not common practice to use gypsum for
> shear
> walls yet we still build buildings with plywood sheathing.  What are we
> doing wrong?
>
> What fire rating are you dealing with?  Is it that plywood could be used
> but since that may require another layer of gypsum that it is cheaper to
> use gypsum board for the shear wall?
>
> Mark Gilligan
>
>
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>
> >
> We use gypsum for lateral force resisting where fire rating prevents the
> use of plywood sheathing.  For design help the Light Gauge Steel Engineers
> Association publishes data for bacing with gypsum, it references table 3
> 1997 UBC and allow for two sided application values up to 850 plf with
> screws at 4/4.   this 850 must be divided by the recommended safety factor
> of 2.5 yeilding 340 plf.  LGSEA has a TECHNICAL NOTE booklet call Vertical
> LAtera Force Resisiting System with this data and desing examples.
>
>
> Jeff Fertich, PE
> Gettysburg, PA
> <
>
>