We are applying for an ADU in San Mateo, ca. 640 sf 1 bed 1 ba.Just the permit will cost about 10 k, with all the green building, demo recycling, all kinds of bureaucracies.However, the added value is around $800/sf, or $400k ish.The actual building cost we estimate around 100k-130k.

If the tenants are on longer term leases, you will need to honor that lease to its conclusion, or negotiate to transition the tenants over to your lease by mutual agreement.Remember, you will be taking someone's home away from them, so be kind.

I can say on all of the smaller bathrooms I have redone, I have probably only spent that kind of money on one or two.

Be friendly (kind-considerate-respectful), firm (be clear about your expectations and have the moxie to address issues as they arise), fair (comply with the law, no favoritism, appropriate response to the situation) , fast (quick to respond to maintenance requests and other tenant concerns), and flexible (when the situation warrants).

Most common would be a revaluation (this is where the properties in the area are reassessed), this however does not always mean taxes are going up.....Your value increasing and your taxes increasing are 2 vary different things!

When that 0% interest rate period runs out, usually that cost of capital becomes VERY VERY expensive (15+ %)A more commonly used method would be to get a private loan on a note from a friend or family member.  

What kind of process is this and how feasible is it to do while there are tenants in place?

Tenants that are one flat tire away from missing rent will not result in quality cash flow, and yet ironically these type of tenants are the kind that tend to rent in the type of neighborhoods that show the highest pro forma cash flow projections on paper ... too bad those cash flows aren't what you will actually get during a downturn, and you spend much of your time chasing down rent as opposed to growing your portfolio ... too bad that the increases in rents and prices will not tend to keep up with inflation in many of these neighborhoods too ...

My last 2 homes were kind of flip houses.

I want to look thought other school and see if this is a common thing, but has anyone else looked though these?