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Re: Re: WOOD - Engineered Lumber vs. Sawn Lumber

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seaoc(--nospam--at),Internet writes:
One reason not to mix sawn lumber sizes with engineered wood sizes is to 
avoid differential shrinkage of sawn lumber vs. dry engineered wood produ
cts.  Since the latter are already at or near the end use moisture condit
ions when manufactured, they could wind up overloaded if end members (rim
 boards) are regular sawn lumber which can shrink from as manufactured 
to in-service depths. Likewise, if joists or blocking of both types are 
mixed in a floor or roof, high or low spots can be created if the sawn 
lumber dries and shrinks to lesser depth than the engineered wood compone
nt.  To avoid such problems, most producers "force" the specifier into 
using engineered wood for all framing components, to avoid callbacks to 
repair uneven floors, roofs, buckled webs on I-joists, floor squeaks, etc

You make a good point, each condition must be evaluated for its appropriate
use.  But I don't think you can make a blanket statement not to mix engr.
lumber with sawn lumber.  There are instances when drying shrinkage may not
make a difference.  Specifically I would use them for heavily loaded beams,
like the garage door header.  Depending on how it is detailed, the
differential in shrinkage would not make any difference to the building
construction.  If the wall studs shrink, the beam drops with them.  If one
were to mix TJI' floor joists with sawn lumber floor joists, then I could see
problems develop.

Richard Lewis, P.E.
Missionary TECH Team

The service mission like-minded Christian organizations
may turn to for technical assistance and know-how.