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Re: Chimney Flues

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Gerard

Typically, I avoid gyp board shear walls.  Depending on your shears
plywood over gyp board is an option, UBC/IBC plywood shear wall tables
give capacities for this.  Usually, I have the existing gyp board
removed so the sheathing is direct applied to the studs even at fire
rated walls.

Gerard Madden wrote:
> 
> Also, how are other people handling things like 50% decrease in Gyp. Bd. shearwall capacities coupled with about 30-50% increase in base shear (potentially gyp. bd. walls are 100% overstressed in existing structures) Are you calling for removal of sheathing and re-sheath w/ plywood? Or do you put plywd over the (e) gyp. like at a perimeter firewall?
> 
> -gerard
> SF, CA
> 
> Thanks,
> -Gerard
> 
> >>> njineer(--nospam--at)att.net 06/26/01 04:06PM >>>
> Gerard,
> 
> The UBC rules for chimneys and fireplaces are in Chapter 31, in volume 1 of
> the 3 volume set.
> 
> The chapter includes a chart for sizing flues based on the chimney height
> and fireplace opening size.
> 
> I've seen old fireplace/chimney systems with more than one fireplace served
> by a single flue, and I don't see a rule against that in the UBC.  The rules
> imply a flue serving a single fireplace, but it doesn't seem to be stated
> explicitly.  My concern would be the possibility of an odd draft condition
> drawing smoke from the chimney into a room with an unused fireplace, though
> it seems unlikely since smoke should rise in the flue rather than fall into
> a cold fireplace.
> 
> James Amrhein wrote "Residential Masonry Fireplace and Chimney Handbook"
> published by Masonry Institute of America.  It covers everything you need to
> know about building the kind of fireplace and chimney that has become
> conventional in the western U.S.
> 
> Also check out http://www.rumford.com for information on the Rumford
> fireplace design -- quite different form the conventional design, plus lots
> of general information on fireplaces and chimneys.
> 
> Nels Roselund
> Structural Engineer
> South San Gabriel, CA
> njineer(--nospam--at)att.net
> 
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-- 
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Forrest T. Braun, P.E.
BBFM Engineers, Inc.
Ph (907)274-2236
Fx (907)274-2520
Anchorage, Alaska
http://www.bbfm.com
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