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Re: OSB vs Plywood

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         (__)                  Dennis S. Wish PE                    

Dear Don, 
Good question.  First, I don't assume the competency of any contractor that 
might build from my plans. I assume that my plans are no different from any 
instructions of assembly and the more information that is on the plan, the 
better chance the finished design will be the way I percieved it when 
creating the design. 
I have one contractor who I happen to be friends with outside of work. His 
framer is one of the best in the trade, but my friend (who is the general) 
lacks the knowledge of foundations and framing. This is a dicotomy since he 
is responsible for the work that his framer does and should be more rather 
than less competitent. Therefore, I know that I am going to spend more time 
on this job during construction than I would on another in order to guide the 
general and to educate him as to what his framer's responsiblity is.
Currently, I have two projects where the licensed GC is less knowedgable than 
his hired subs.  In most cases, if I feel comfortable with the subs I place 
more responsibility in them and ask that they be my contact so my 
instructions are given first hand.
Rather than take the time in this post, please refer to my next email with 
the Subject - Pathways. I think that Don and others will be interested in 
this pre-construction planning to improve construction problems.

I personally don't believe in penalizing the homeowner or building owner by 
trying to compensate for what may or may not happen in the field. The only 
thing that I do when seismic governs is to use a more conservative Rw for 
plywood based shearwall systems (Rw - 6 rather than 8).
I believe the code provisions in the '97 UBC is overly conservative resulting 
from the pressure by the Insurance industry after 20 Billion in damages from 
Northridge earthquake. 
I think the question needs to be asked - "Would we have had the extent of 
damage to residential construction from the Northridge earthquake if all 
plans were engineered or engineered prescriptive measures (the Conventional 
framing presciptive measures are not equal to minimum engineered solutions), 
would the extent of damage been comparable? In other words, was the current 
code deficient?
I read a report that Don Carr helped author on the damage caused by Hurricane 
Andrew. The conclusion of the article was that the code provided an adequate 
level of performance. I apologize if I get this wrong, but one of the reports 
I read claimed that the code was inadequate in the installation of the roof 
diaphragm with 6d nails. It suggested changing this requirment. (I'm not sure 
if this was the same article that Don was listed as authoring). 
If codes are adequate, then why should we overdesign to compensate for 
construction quality?

I know that I am one of the most vocal advocates against overdesigned codes 
used to compensate for construction defects. I apologize for constantly 
hammering on this topic, however, I would really like to hear other comments 
and suggestions that can be constructive to help resolve the problems.


Dennis S. Wish PE
Structural Engineering Consultant