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Swimming Pool Enclosures - Timber vs. Steel

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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