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Re: Swimming Pool Enclosures - Timber vs. Steel

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We have done several pool buildings in Anchorage and Fairbanks that have
included both wood and steel structures.  The concern with both is
condensation on or within the structure.  Having a well controlled
atmosphere is critical for long term performance of the structural
system.  The Alaska yellow cedar is a good choice because of its natural
resistance to decay.  I would extended it through the decking as well
since the decking may be in the location of the dew point.  The first
pool in Anchorage was glulam arches with 4 " T&G decking.  Inadequate
insulation lead to the dew point being within the wood, actually down in
the arch, which then rotted out.  The building no longer exists.  More
resent construction has used untreated Douglas fir glulams and are
performing well.  We have also used metal deck over open web steel
joists supported on tube steel trusses.  A high quality vapor barrier
and adequate insulation needs to be installed over the decking to keep
the dew point above the vapor barrier at all times thus removing the
potential for condensation on the steel or within the wood. In addition,
a high quality paint system needs to be specified for added protection
of the steel.

> Peder Golberg wrote:
> I have a question on the material of choice for framing a roof over an
> indoor swimming pool.   I have gotten involved in the middle of a
> project to build a community swimming pool that is way over budget.
> The plans for the roof structure currently contains 90 foot long
> Alaska Yellow Cedar glu-lam beams at 15 ft on center with 4x laminated
> Douglas Fir decking.     From the mechanical engineer, the building
> will be kept at 85 degrees and have about 50% humidity.   From my
> Timber chart, this equals about a 10% equilibrium moisture content in
> the wood.   Does anyone see any draw backs to using un-treated Douglas
> Fir for the girders  (90 feet long exceeds all nearby treating
> plants).  Douglas Fir is less than half the cost of Alaska Yellow
> Cedar in my area and we have been asked to investigate alternatives.
> The current plans are based off of other pool designs in the area that
> all seem to have Cedar or pressure treated Douglas Fir.   Another
> option I'm proposing is a treated Douglas Fir truss with steel hidden
> connections.
> I have also provided the architect with an exposed steel girder truss
> option that appears to be the least expensive of all the
> alternatives.   I have reservations with the steel based on the
> chlorine gas, corrosion, and indoor pools even with
> galvanizing.   Galvanizing 90 foot long trusses may be an issue
> also.   Any noted issues or successes with steel used over indoor
> pools?   I have used galvanized steel before for a hotel pool which
> was hidden by the ceiling.
> Thanks in advance for any comments.
> Peder Golberg, P.E., S.E.
> Portland, Oregon

Forrest T. Braun, P.E.
BBFM Engineers, Inc.
Ph (907)274-2236
Fx (907)274-2520
Anchorage, Alaska

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