Stephen,
In our practice we also receive requests from contractors for our CAD files. Our internal policy does not allow us to give CAD files direct to contractors. If requested in writing by our Client, we provide a copy of the files without charge except for handling to our Client, (not the contractor directly). We provide a "read only" CD such that the information/data as provided cannot be changed. Under AIA contracts the Client has a licience to use the design so if they provide it to the contractor that becomes their responsibility and your rights under the contract are intact.
The contractor must save a copy to have any access to make changes so there is a clear distinction between what was provided and any changes thereafter.
Of course the CD and the transmittal includes the appropriate disclaimer and copy right language. Depending on your actual contract with the Client, you should be retaining the Ownership of the design. We suggest you also consult with your insurance carrier for any additional language.
Good Luck.
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Martin Ucker AIA
Hankins & Anderson Inc
La Mesa CA
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