Proper structural engineering likely to be required
Required in 95% of cases
In my area (King County, Washington State, USA), in 95% of cases a formal structural engineering signoff is required to obtain a building permit. In practice most houses are enough out of the ordinary to need this, and certainly my house design is a lot out of the ordinary, so it definitely needs proper structural engineering. The structural engineering needs to be done by a structural engineer who is licensed for your area. It is not something that you can do yourself because you don't have a license.
Details regarding structural engineering are here .
My structural engineering set of drawings
Here is the complete set of structural engineering drawings submitted for my house...