I don’t understand why they are so strict.

Told him to leave ill do it myself.)Bad sill plate on rear corner (contractor)Replace front porch postsBuild backporch stepsDemo barnInstalling concrete footers under home, laying block and shimming to your jacked levelSetting house back down on blocks and reattaching to foundationRemove floor and portions of subfloor in kitchen & back porch and replacement Window repairTemporary power pole (electrician)Electrical service upgrade, outlet replacement and GFCI Install (mix of Electrician and us)Label panels (electrician)All exposed wiring must be protected (basically just replaced all of it)Replace missing light fixtures (new fans throughout)Build wall in living room to convert to 3rdbedroomRe plumb house and pressure test plumbing (plumber)Install smoke detectors hardwired to meet code (electrician)Water Heater electrical line, and core discharge for water heater under house (plumber)Tear out Old ac unit under houseWindow screensWindow locksBackflow prevention valve (plumber)Fart fan ventilation for bathroomApproved Address Number DisplayedFlaking paint abatement interiorClothes Dryer exhaustPaint Untreated woodRemove all debris, Remove old tiresRemove chain link fenceTreat house for black antsPoly floorsMud and paint wallsAppliancesDoors/locks.Roof patch, remove 12x24 section, cut out rot, sister in new beams, put new plywood & shinglesPiles and piles of new electrical wiring (electrician/us)Sand all walls and spray texture ceiling and walls with joint compoundPaint whole house inside and outNew trim everywhere.Sand the every living hell out of the floors (100 hours of labor + help)Gutters and french drainNew mailboxA/c Unit.

What’s the group code?  

So the lot size is not much of a constraint especially with new offset requirements for 2020.Now my question is strictly from the financial point of view, how do I go about deciding the size (sq.ft.) of the ADU?

It needed a fairly decent rehab to bring it up to code.

Talk to code.

Just to clarify the 280k is what I can ask IF I do full remodel, which I will over time but 5-10k is just to bring it to code for bank finance.  

Look for the code enforcement inspection map on the city’s website to find who does your area. 

Doing any investing yourself or strictly working on the lending side?

I need to find a trustworthy structural contractor to help that is knowledgeable in building code for that area.