In brief, the regulations require at least one hundred fifty (150) square feet of floor space for the first occupant and at least one hundred (100) additional square feet of floor area for each additional occupant. More details are below.

Sec. 16-267. – Light; ventilation
No person shall occupy as owner-occupant or let or sublet to another for occupancy any dwelling unit designed or intended to be used for the purpose of living, sleeping, cooking and eating therein, nor shall any vacant dwelling be permitted to exist which does not comply with the following requirements:

(1) Habitable rooms—Light. Every habitable room shall have at least one (1) window or skylight facing directly to the outdoors. The minimum total window area, measured between stops, for every habitable room shall be eight (8) percent of the floor area of such room. Whenever the only window in a room is a skylight-type window in the top of such room, the total window area of such skylight shall equal at least fifteen (15) percent of the total area of such room.

(2) Same—Ventilation. Every habitable room shall have at least one (1) window or skylight which can be safely opened, or such other device as will adequately ventilate the room. The total of openable window area in every habitable room shall be equal to at least forty-five (45) percent of the minimum window area size or minimum skylight-type size, as required, or the room shall have other approved equivalent ventilation.

(3) Bathroom. Every bathroom shall comply with the light and ventilation requirements for habitable rooms except that no window or skylight shall be required in adequately ventilated bathrooms equipped with an approved ventilation system.

(4) Electric lights and outlets. Every dwelling shall be adequately and safely wired for electric lights and convenience receptacles. Every habitable room and hallway shall have provisions for adequate lighting and other necessary electrical service.

(5) Light in public halls and stairways. Every public hall and stairway in every multiple dwelling containing five (5) or more dwelling units shall be adequately lighted at all times. Every public hall and stairway in structures devoted solely to dwelling occupancy and containing not more than four (4) dwelling units may be supplied with conveniently located light switches, controlling an adequate lighting system which may be turned on when needed, instead of full-time lighting.
(Code 1962, § 6-51)

Sec. 16-268. – Electrical systems
No person shall occupy as owner-occupant or let or sublet to another for occupancy any dwelling or dwelling unit designed or intended to be used for the purpose of living, sleeping, cooking or eating therein, nor shall any vacant dwelling be permitted to exist which does not comply with the following requirements:

(1) All fixtures, receptacles, equipment and wiring shall be maintained in a state of good repair, safe, capable of being used and installed and connected to the source of electric power in accordance with the adopted electrical code of the city.

(2) The minimum capacity of the service supply and the main disconnect switch shall be sufficient to adequately carry the total load required in accordance with the electrical code of the city.
(Code 1962, § 6-52)

Sec. 16-269. – Exterior and interior of structures generally.
No person shall occupy as owner-occupant or let or sublet to another for occupancy any dwelling or dwelling unit designed or intended to be used for the purpose of living, sleeping, cooking or eating therein, nor shall any vacant dwelling building be permitted to exist which does not comply with the following requirements:

(1) Foundation. The building foundation walls, piers or other elements shall be maintained in a safe manner and capable of supporting the load which normal use may cause to be placed thereon.

(2) Exterior walls. The exterior walls shall be substantially weathertight and watertight, and shall be made impervious to the adverse effects of weather and be maintained in sound condition and good repair.

(3) Roofs. Roofs shall be maintained in a safe manner and have no defects which might admit rain or cause dampness in the walls or interior portion of the building.

(4) Means of egress. Every dwelling unit shall have two (2) safe, unobstructed means of egress with minimum ceiling height of seven (7) feet leading to a safe and open space at ground level.

(5) Stairs. Every inside and outside stair shall be safe to use and capable of supporting the load that normal use may cause to be placed thereon; and shall be kept in sound condition and good repair.

(6) Porches and appurtenances. Every outside porch and any appurtenance thereto shall be safe to use and capable of supporting the load that normal use may cause to be placed thereon; and shall be kept in sound condition and good repair.

(7) Windows and doors generally. Every window, exterior door and basement or cellar door and hatchway shall be substantially weathertight, watertight and rodent proof; and shall be kept in sound working condition and good repair.

(8) Windows to be glazed. Window panes or an approved substitute shall be maintained without cracks or holes which allow passage of air.

(9) Window sash. Window sash shall be properly fitted and weathertight within the window frame.

(10) Hardware. Every exterior door shall be provided with proper hardware and maintained in good condition.

(11) Door frames. Every exterior door shall fit reasonably well within its frame so as to substantially exclude rain and wind from entering the dwelling building.

(12) Screens. Every door opening directly from a dwelling unit to outdoor space shall have screens and a self-closing device; and every window or other device with opening to outdoor space, used or intended to be used for ventilation, shall likewise have screens, tightfitting, free of holes and not nailed to the window frame or sash. Dwellings containing central heating furnaces and adequate cooling equipment for mechanically ventilating the building year around are not required to have screens on door or window openings.

(13) Accessory structures. Garages, storage buildings and other accessory structures shall be maintained and kept in good repair and sound structural condition.

(14) Interior floors, walls, partitions, ceilings. Every floor, wall, partition and interior ceiling shall be substantially rodent proof, shall be kept in sound condition and good repair and shall be safe to use and capable of supporting the load which normal use may cause to be placed thereon.

(15) Structural supports. Every structural element of the dwelling shall be structurally sound and show no evidence of deterioration which would render it incapable of carrying loads which normal use may cause to be placed thereon.

(16) Protective railings. Protective railings shall be required on any unenclosed structure over thirty (30) inches above adjacent finish grade or on any steps exceeding four (4) risers. Interior stairs and stairwells more than four (4) risers high shall have handrails located in accordance with requirements of the building code. Handrails or protective railings shall be capable of bearing normally imposed loads and shall be maintained in good condition.
(Code 1962, § 6-53)

Sec. 16-270. – Space and use.
No person shall occupy as owner-occupant or let or sublet to another for occupancy any dwelling or dwelling unit designed or intended to be used for the purpose of living, sleeping, cooking or eating therein, nor shall any vacant dwelling building be permitted to exist which does not comply with the following requirements:

(1) Space in dwelling unit. Every dwelling unit shall contain at least one hundred fifty (150) square feet of floor space for the first occupant thereof and at least one hundred (100) additional square feet of floor area per each additional occupant.

(2) Space in sleeping rooms. In every dwelling unit of two (2) or more rooms, every room occupied for sleeping purposes by one occupant shall contain at least seventy (70) square feet of floor space, and every room occupied for sleeping purposes by more than one occupant shall contain at least fifty (50) square feet of floor space for each occupant thereof.

(3) Minimum ceiling height. At least one-half of the floor area of every habitable room, foyer, hall or corridor shall have a ceiling height of at least seven (7) feet; and the floor area of that part of any room where the ceiling height is less than seven (7) feet shall not be considered as part of the floor area in computing the total floor area of the room for the purpose of determining the maximum permissible occupancy.

(4) Occupancy of dwelling unit below grade. No basement or cellar space shall be used as a habitable room or dwelling unit unless meeting all specifications for habitable rooms.
(Code 1962, § 6-54)

Source: https://www.municode.com/library/nc/wilmington/codes/code_of_ordinances?nodeId=PTIIITECO_CH16BUBURE_ARTVMIHOCO_DIV4MISTEQFA_S16-269EXINSTGE