Adding a complete unit to a SFR to make a duplex

[Matt Geerts]

Can anybody shed some light on their experience adding a unit to an existing building?

Lets say I can get a house that will already cash-flow decently and the outside is ugly. It is zoned R2 and the frontage, area and coverage details work (just to get that conversation out of the way).

I strip off the siding, pour a foundation at the back of the house, build a complete unit and then re-side the entire house at once so it blends.

Is this a worthwhile upgrade? Of course there are complications like tapping into sewer, water, gas and electric - are these show-stoppers? It will have the nice benefit of everything being metered separately.