I am not sure how much electricity/gas would be.

I am very pro EV and electric vehicles, we want the tenants with these cars. 

And fined retroactivally.Additionally, if a tenant has an accident (slips/ falls/etc), or something goes hugely wrong with the dwelling (fire/electrical/etc), your insurance WILL NOT COVER the claim.

But the electrical will be properly secured as well with a moisture barrier.

Also utilities and sitework should be less as you do not need to bring in two electrical services, water services and run two sewer services and connection fees.

This is the biggest house I’ve flipped so far.the other two were about 1800 ft.² single-story homes.As far as ADU goes, I have already passed framing, electrical, plumbing, insulation, sheer wall, and HVAC and installed all windows & door.

(The arrangement was that they pay me for electricity because they share electric with other unit.) and they started to complain about roof leak which caused them hardship.

Seems renovating this part of the attic would require ceiling insulation, drywall, flooring, electrical outlets, & heating source.My concern is that a reappraisal wouldn't add anything to legal square footage. 

You'll either have to convert the house into a legal duplex by getting permits from the city or you install an electrical panel split so that you can track each units/bedrooms of their power usage.In terms of lending world and being to use the rental income, the property needs to be a legal duplex meaning title must be shown as a multifamily and not a single family in order to use the rental income separately.

If it was built before, say, 1960 there may be a slew of electrical work you'll need to do to stay in regulations with current times and, of course, for the safety of a future buyer.