CWB1, your feedback is appreciated, but it's clear that you do not work in the Architecture/Engineering/Construction industry for buildings. Our contracts are typically for professional services to perform the structural design of a building and produce a set of stamped construction drawings (i.e., blueprints), which is our deliverable and is typically pdf files these days of course. CAD files are usually either not addressed by the service agreement (i.e., contracts), or specifically excluded from the service agreement by savvy practitioners that have been down that road a few times. We are not hired to produce CAD files, we are hired to design a building and produce a set of stamped construction drawings. Once we have done that, we are not obligated to hand over cad files. What if I drafted everything by hand? Would I be obligated to then redraw everything in CAD if for example a rebar detailer asked for my CAD files? I rarely get asked for CAD files, but when I am asked, I either refuse, or I have a separate release/agreement that the recipient must agree to, which basically says that CAD files are being provided for convenience only and that has a bunch of legal ease about liability for use of the files. I charge an "administrative fee" for the time and effort to assemble and prepare the files for transfer. This is by no means double billing, because like I said, we were never contracted in the first place to provide CAD files.
Of course, others' mileage may vary, and other clients may try to force contracts that require production of CAD files, specific CAD software packages, release of all IP, etc. The larger and more powerful the client, of course the more likely they are to do such things.
Regarding IP, unless their is a contract in place to the contrary, of course we own the IP. How can the design of a one off "thing" of any kind, in this case a building, not be proprietary?