You don't have to convert that property back into a two-family house. You can just rent out the second condo. The trick will be getting Somerville to tax you as an owner-occupied two-family home. Adam Dash is the lawyer in Somerville who knows everything about the way the city works on stuff like this.
If you live in 02144, I don't think you will get enough rent to make this worth your while.
typically, questions like this best answered by lawyers since they need to be involved in legal work associated with any conversion.
Yet... my question to you is why are you asking such a question? What are you really concerned with? The main purpose of converting into condos is to establish a common set of rules for all to share and a condo fee to maintain common areas. If you own both units in a 2-family house you set your own rules and maintain the property as you wish.
If down the road you'd want to sell one or both you might, actually, want the condo papers. Also, if you rent out one unit or both you'd have some business expenses you could deduct from taxes, such as the part of a condo fee used to maintain the rental property! If you have anymore questions or need assistance, feel free to contact me http://www.boc-re.com. I'll be happy to give you reference to RE lawyer(s) if you'd like... Good luck!
Thanks for your answer -- but we're in a 2-family house, and we would rent out one unit if we owned the whole building. We wouldn't convert it to a one-family house.
I know that to condoize, you have to pay architectural and legal fees and apply to the city. So I wondered what the process is to "un-condoize" a house so that it's owned by one owner again?
We're also not looking to move; we'd like to stay here but would rather own the whole (2-unit) house.