What are the biggest mistakes when converting to a duplex?

[John D.]

I am curious if anyone has list of common mistakes that people make when trying to convert a SFR to a duplex?

Are there specific types of properties that work best for a conversion to a duplex? Are there properties that do not work well for a conversion?

[John D.]

Thanks @Eliott Elias and @Matthew Morrow, this is great info. I do like the idea of doing the upfront work to convert something if it will add value and create good cashflow, but yes - the biggest pitfall could be under estimating the rehab cost. Having a contractor that I can trust will be the most important thing here I think.