Many North American cities have a lack of middle-density housing (aka the "missing middle") and Lansing is a perfect example.
Lanstronaut Cedar500 created this visualization of where it is legal (black) and illegal (red) to build /convert a residence to a duplex.
"New duplexes are not allowed in 80% of Lansing, and 88% of areas with single family homes. A duplex is a way to add affordable unites to an existing area, both adding homes and lowering housing costs. Historically, multi-family homes such as duplexes were banned with the intent of excluding lower income, often minority families from neighborhoods."
Important to note that Lansing does have duplexes operating in areas not zoned for them.
"If we were to change code to allow [duplexes], we could basically put anything we want in there. Zoning code allows for all sorts of rules like 'must be owner occupied', 'an individual can not own more than 6 units in this zone type' etc.
"Also many of Lansing's existing duplexes are actually entirely owner occupied, meaning there is no tenant at all. Both people living in the property own their half, but co-own the entire structure, paying together for repairs and being able to sell their halves at their own leisure. Historically this was a huge way people built their initial equity; making small mortgage payments on a small property instead of permanently kissing the money goodbye via rent, or not being able to afford a starter home at all.
"While clearly the strictest method, the 'duplex must be owner occupied' virtually makes slumlording impossible by limiting someone to a single property, that while they still could let [their property] become dilapidated, they need to live in it too."