This is actually not such a simple question. There is copyright (the right to content) and the right to reproduce (in case of building - right for keeping, using etc. of project). Transfer by the author of the right to reproduce it does not mean the loss of author right. For example, if you gave a book or an article to a publisher, then the contract clearly states what the publisher can do with it (and in what spatial and temporal framework) and for what reward. But by no means he can use this work without mentioning the name of the author, etc.
There are whole section of the Law, very voluminous and professional.
Marina Mihaila ... You have good point of view.. we all respect your opinion, ..it consider a deep point of conflict between whom create the idea and whom buy... Actually, I'm with the designer .... by the way.. . I have another question about the designer. if you like to answer, you will find it between my questions...
Ownership of copyright is the right of the architect unless the owner agrees with the contrary to be a proven paragraph in the contract between the parties.
Copyrights can be transferred, so both of them or any one of them can own the copyrights of the architectural project depending on the agreements between them.
However, the architect owns the intellectual property of his architectural work, which means the client can not change, edit or modify the architectural work.
I invite you read my paper
Article Architectural Copyright: Potentialities and Limitations with...