As an Architect, I see a few other things others haven't mentioned.

I'm an architect (from PA) and we get Geotechnical reports done during the design phase so we can design the foundations appropriately. 

After backing out the costs for rebuilding the garage and 1 bedroom unit below, which was necessary to support the second floor ADU we were at $250 per square foot for 1,000 new square feet, but i am an architect so i saved money on plans and managed the construction myself.

The entire development team is in place and engaged (Attorneys, architects, surveyors, engineers, builder, contractors, material suppliers, etc. etc.), and multiple letters of interest and soft commitments to fund the construction at permit.

Our team, comprised of talented architects, engineers, and construction professionals, is passionate about engaging in insightful discussions within the real estate investment realm.About Cronus:Hailing from Houston, Cronus has earned its reputation for design and build excellence.

Our team of agents has flippers, architects and developers so there is good chance we could be quite helpful to you.

Although I haven't done my 1st deal yet I have the program Home Designer by Chief Architect that my husband and I have used to create our dream home floor plans.

You need to check with an architect.

I recommend that you use a architect any time you are going to make a significant change to a property and make sure you select the architect not your contractor.

The Los Angeles Architects office I spoke to last week suggested there were ways round this and that people were putting in permit application for a large building along with an assessory building.