In each district each structure hereafter erected or altered shall be provided with the yards specified, and shall be on a lot of the area and width specified in Chapters 18.25 through 18.45 CMC. No open space or lot required for a building or structure shall during its life be occupied by or counted as open space for another building or structure. Exceptions to the district requirements for building lots and yards follow:

In each district each structure hereafter erected or altered shall not exceed the heights specified in the district requirements in Chapters 18.25 through 18.45 CMC.

Height limitations shall not apply to church steeples, hospitals, sanitariums, barns, silos, farm structures, chimneys, flagpoles, public utility poles, radio and television towers or aerials, cooling towers, and water tanks; and industrial structures when required by manufacturing process but not to exceed 25 percent of the area of the lot.

In each district each structure hereafter erected or altered shall be provided with off-street automobile storage as specified in the district schedule, Chapters 18.25 through 18.45 CMC. No off-street automobile storage space required for a building or structure shall during its life be occupied by or counted as off-street automobile space for another building or structure, but may be counted as yard space.

In each business and industrial district each structure hereafter erected or altered shall be provided with off-street loading and unloading facilities as specified in the district schedule, Chapters 18.25 through 18.45 CMC.

It is the intent of this title that there shall be but one main structure plus any permitted accessory structures on any lot used for residential purposes; also, that accessory structures shall not include living quarters. No mobile home shall be parked permanently or temporarily on any lot which already contains another main structure, whether such main structure is used for residential or business purposes.

No lot shall be reduced in area so that yards and other open spaces total less than the minimum area required under this title.

In a residence or local business district no fence, wall shrubbery, sign, marquee, or other obstruction to vision between the heights of three and one-half feet and 15 feet above street level shall be permitted within 20 feet of the intersection of the right-of-way lines of two streets or railroads or of a street and a railroad right-of-way line.

Accessory structures within 25 feet of the rear lot line of a corner lot shall be set back the minimum front yard depth required on the side street.

On any lot which, at the time of adoption of the ordinance codified in this title or at the time this title is changed by amendment thereafter, may be reduced in area by widening a public street to a future street line as indicated on the duly adopted "major street plan," or as same may be hereafter amended, the minimum required yards, the minimum required lot area, the minimum required lot width and the maximum building area shall be measured by considering the future street line as the lot line of such lot.

The Board of Adjustment may require the conduct of any use, conforming or nonconforming, which results in unreasonable noise, smoke, gas, vibration, fumes, dust, fire, radio interference, or explosion hazard or nuisance to surrounding property to be modified or changed to abate such hazard to health, comfort, and convenience. The Board of Adjustment may direct the Building Inspector to issue an abatement order, but such order may be directed only after a public hearing by the said Board, notice of which shall be sent by registered mail to the owners and/or operators of the property on which the use is conducted in addition to due notice by advertisement in a newspaper of general circulation. A hearing to consider issuance of an abatement order shall be held by the Board of Adjustment either upon petition signed by any person affected by the hazard or nuisance or upon the initiative of the Board. An abatement order shall be directed by the Board of Adjustment only upon reasonable evidence of hazard or nuisance and such order shall specify the date by which the hazard or nuisance shall be abated.

In the case of a housing project consisting of a group of two or more buildings to be constructed on a plot of ground of at least four acres not subdivided into the customary streets and lots and not to be so subdivided or where existing or contemplated street and lot layout make it impracticable to apply the requirements of this title to the individual buildings in such housing projects, the application of such requirements to such housing projects shall be done by the Board of Adjustment with the advice of the Planning Commission, in a manner that will be in harmony with the character of the neighborhood, will ensure substantially the same character of occupancy, a density of land use no higher and a standard of open space at least as high as required by this title in the district in which the proposed project is to be located, and will provide layout design and public utilities in harmony with the general requirements and minimum standards of design of the subdivision regulations of the City.

In no case shall the Board of Adjustment authorize use of a building height or building area prohibited in the district in which the housing project is to be located.