.• On any lot with an existing single-family dwelling unit, where regardless of zoning, the lot has any of the following General Plan Land Use/Transportation designations:- Residential Neighborhood- Mixed-Use Neighborhood- Urban Village or Urban Residential- Transit Residential or Rural Residential- Downtown- Mixed-Use Commercial• On two-family (duplex) lots and on multifamily properties• In a low-density cluster development if it conforms to development standards of the R-1 zoning district, and the development and use standards of the low-density cluster permit.Minimum Lot Size3,000 square feetNo minimum lot sizeMinimum Setbacks from Rear and Side Property Lines0 feet for 1-story conversions and new construction.5 feet for second-story ADUs constructed above a garage or accessory structure.0 feet for 1-story conversions and new construction.4 feet for second-story ADUs constructed above a garage or accessory structure4 feet minimum rear and side setbacks required for detached ADU in multifamily developments.Maximum HeightFor detached ADUs:Single story – 18 feet maximumSecond story – 24 feet maximumAttached ADUs are subject to the height limits of the main home.Single-family properties - No change in height requirements.Multifamily properties - 16 feet maximum height for detached ADUs.Rear Yard CoverageArea covered by the ADU, accessory buildings, and accessory structures, except pools, shall not exceed forty percent (40%) of the rear yard.Area covered shall not exceed forty percent (40%) of the rear yard or up to 800 square feet, whichever is greater.Detached ADU Allowed LocationsRear yard only, at least 6 feet away from primary dwelling.May be attached to a detached garage or other existing accessory structure.Must meet minimum setbacks for an accessory building in accordance with Section 20.30.500.No changes except that ADUs that exceed forty percent (40%) of the rear yard must maintain minimum 4 foot side and rear setbacks.

.• On any lot with an existing single-family dwelling unit, where regardless of zoning, the lot has any of the following General Plan Land Use/Transportation designations:- Residential Neighborhood- Mixed-Use Neighborhood- Urban Village or Urban Residential- Transit Residential or Rural Residential- Downtown- Mixed-Use Commercial• On two-family (duplex) lots and on multifamily properties• In a low-density cluster development if it conforms to development standards of the R-1 zoning district, and the development and use standards of the low-density cluster permit.Minimum Lot Size3,000 square feetNo minimum lot sizeMinimum Setbacks from Rear and Side Property Lines0 feet for 1-story conversions and new construction.5 feet for second-story ADUs constructed above a garage or accessory structure.0 feet for 1-story conversions and new construction.4 feet for second-story ADUs constructed above a garage or accessory structure4 feet minimum rear and side setbacks required for detached ADU in multifamily developments.Maximum HeightFor detached ADUs:Single story – 18 feet maximumSecond story – 24 feet maximumAttached ADUs are subject to the height limits of the main home.Single-family properties - No change in height requirements.Multifamily properties - 16 feet maximum height for detached ADUs.Rear Yard CoverageArea covered by the ADU, accessory buildings, and accessory structures, except pools, shall not exceed forty percent (40%) of the rear yard.Area covered shall not exceed forty percent (40%) of the rear yard or up to 800 square feet, whichever is greater.Detached ADU Allowed LocationsRear yard only, at least 6 feet away from primary dwelling.May be attached to a detached garage or other existing accessory structure.Must meet minimum setbacks for an accessory building in accordance with Section 20.30.500.No changes except that ADUs that exceed forty percent (40%) of the rear yard must maintain minimum 4 foot side and rear setbacks.

It is possible she could be charged with accessory before the fact, but that would be a little tougher, but not impossible.

There are different forms of house hack (Accessory Dwell Unit (AUD), Mother in Law (MIL), rent by room, rent one side of a duplex,....) 

We just tried to do this on a house and then realized that Corpus is very unfriendly to Airbnb unless you have a commercially zoned unit or you're Airbnbing an accessory dwelling.

Some others that I've used/am considering/had recommended to me:On-site, coin-operated laundry machines (most relevant for multi-family properties)Renting out storage space in basement or on-site shedRenting out unused off-street parking (where I live, winter RV parking is at a premium)Converting non-conforming to conforming rooms (including basements) to allow for re-organization and classification as bedroomsAdding accessory dwelling unit(s) to your property (may not even require separating lots)Separating utility metering (or installing individual unit readers) on multi-unit properties that are currently metered togetherDepending on your market, furnishing a portion of your units and renting them out fully furnished to shorter-term renters*Some (most) of these will depend on how individual properties are zoned, what zoning requirements are in your locale, and what there is demand for in your market.

If you are an owner occupant, build and ADDU and then move from the property the ADDU reverts to an "Accessory Structure," and if rented as a residence will be considered "non-conforming" by the city, and may be subject to code compliance issues a s potentially legal action.

I would budget more than $1,500 for the furnace unless you're going to do the labor yourself they start at 1200 and go up to well over 3,000 depending on the size of the property the cheapest plumber ever quoted me was $1,000 labor and then there was another 200 hundred dollars worth of accessories once you start connecting the vents.

An adult and child day care center as an accessory use when located within a school or religious facility building.

Reply from City of Columbus:In almost all cases at this time, a second dwelling (also known as an Accessory or Auxiliary Dwelling Unit (ADU)) unit would require a zoning use variance prior to permitting and construction and must meet the development standards as shown on the attached as for any other dwelling unit unless granted a variance as part of the use variance, also known as a Council Variance.The Columbus Zoning Code which contains all the requested standards is online at https://www.municode.com/library/#!