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Re: RIGID DIAPHRAGM IN WOOD FRAMED CUSTOM RESIDENCES

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Pat,
 
The owner needs to be helped to understand early in the design phase that the structure of a house is a system, not an assembly of components, and changes to the structural system may have consequences.  When the owner wants to make a change, you need to explain the impact of the change on the system and provide alternatives to accommodate the proposed change.  The owner is then able to participate in the decision on the basis of his judgement balancing his costs and his benefits.
 
Now, if the addition of a shear wall with holddowns is one of the alternatives, it may need to include drilling a hole thru the footing at the holddown location and tunneling under the footing to install a block of concrete into which the holddown bolt can be embedded so that the weight of the footing is engaged.  I've done this for heavy uplift loads.  For lighter loads, deep embedment of the holddown bolt in epoxy adhesive in a hole drilled into the footing may be a solution -- in this case, I would require the depth of embedment to be at least the depth of embedment required for a cast-in-place anchor to develop the needed weight of the footing.
 
Nels
 
Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net