Upgrade Question: Should I lift my house or dig deeper?

[Louis W.]

My family got a property in Oakland CA. The first floor of the home is too low to qualify as a separate unit. It is around 12 inches too short. Also, the first floor is already 20 inches below ground level. So, which option is better? Lift the house or dig deeper? 

Another question is when should we upgrade? Currently, there is a construction boom in Oakland, making labor and material more expensive. Should we wait for a down period to do this upgrade?

Thanks.