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Re: SW's w/ steel light gauge construction

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> In a message dated 8/5/99 7:50:14 AM Pacific Daylight Time,
> michellekb(--nospam--at) writes:
> << Hi fellow Engineers:
>  We are in the process of designing some 4 story steel light gauge
>  buildings.  Our lateral system is single sided plywood shear walls.  We
>  had a meeting with a contractor last week and he suggested to the
>  Architect to put the plywood shear walls on the interior face of all the
>  exterior walls to prevent extensive cracking of the stucco due to
>  unevenness of the plywood with non-sheathed areas.  When I heard this I
>  was surprised.  First, we are using a vast majority of the exterior
>  walls for shear walls.  Second, on all the wood framed buildings I've
>  ever done, the plywood has been put on the outside face of the exterior
>  wall to prevent problems with  installation of the plumbing and
>  electrical.  I foresee a lot of problems with this, especially since
>  scaffolding is not going to be provided to install the utilities at the
>  upper levels they are going to have to do it from the inside face.  Does
>  this seem reasonable?
>  Any insight that you can share with me would be appreciated.
>  Thank you,
>  Michelle Biron
>   >>

I've always preferred sheathing the outside face of buildings because the
plywood continues over the rim joist/blkg. at the floor level and provides a
direct path of load transfer. With sheathing on the inside face each floor
represents a break in the shear "flow" and must be accomplished with fastenings
to sole plates, rim/blkg. and top plate to accomplish the same thing.

As for the comment regarding stucco cracking due to the unevenness of the
plywood at discontinuous areas, this may be an argument. The makeup in this
thickness would/could be accomplished with additional fillers however how come I
get the feeling this wouldn't be preferred due to costs?? If variable thickness'
of coating are proposed then perhaps these comments are worthy.

Another point about application of stucco would be that installing directly over
a solid sub sheathing does create drying/shrinkage problems. Double and triple
papering probably helps but the fact is it is a cement based product and just as
we try to allow two sided expiration on slabs on grade, stucco should be
regarded similarly. Installing against open stud faces will allow the backside
to cure better and therefore crack less. All this said, I'd still throw my
weight behind the sheathing on the outside because of the reasons stated above,
and ask the Architect to provide a thorough review of relief jointing. After the
EQ, will the benefits of an initially pretty building outweigh a safer one?

Lastly, I share your concern about utility penetrations. If you get "outweighed"
on this issue, make sure you make a stink about how careful the subcontractors
have to be around shear wall penetrations. Then stick to it in the field.

Barry H. Welliver
Draper, Utah