I am going to give the bare ownership of my house to my son. Do I need to have a technical diagnostic report prepared before going to the notary?

In principle, no. The technical diagnostic report is mandatory when real property is sold (Art. L.271-4 of the French Construction and Housing Code). Nevertheless, so that your son has all the relevant information and can consent to the gift with full knowledge of the facts, it may be useful to have such a report prepared.