I have been telling my sons to utilize that!

Monthly Expenses: I’m accounting for rent, utilities, and cleaning supplies, but are there other hidden costs I should consider?

You can utilize hard money for a BRRR or flip to get into the game. 

If the property is sub-metered/ if you intend to have the tenants pay utilities make sure to mention that to them. 

Are you utilizing REPS?

It now cash flows beautifully, which I continue to utilize for other my other properties. 

I hired a GC to manage the build out, but there has been no consensus on who is responsible for the utility payments (Water and Energy). 

They need to do all their due diligence including understanding the value that will be added by the ADU, the finance options available, the consequences of adding the ADU (rent control, property taxes, rental limitations, etc), etc.Good luck As with all things, it depends on the investor and the equity.If they are able to leverage existing equity to buy it under a HEL or HELOC, then they are adding equity with no out of pocket expenses, and adding immediate and longterm cashflow to existing stock.We like ADU's because there isn't more land being created in our city that is landlocked...but there is more density available to those with large lot under-utilized sfh.In my market, it typically costs $2 to add less than $1 of value on single build ADUs.  

This process is extensive, requiring community engagement and approval from the City Planning Commission and City Council.Given the predominance of multifamily residential properties in your area, there may be a precedent for such developments.

We want to travel and invest and are considering converting this short term rental to a long term rental to avoid sales tax, paying utilities and general management of the property.