Current UDO document link:
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The UDO does not have a statement that reads "you cannot have a building or structure on a residential lot without a house".
The property is split zoned RS20/RS40, there is only one principal building allowed on the lot by right. You can read the definitions in UDO Section 11, or below for a principal building, accessory structure, and residential building, single family. The attached Principal Uses Table provides all of the uses allowed in the RS20/RS40 zoning districts. There is no principal use for accessory structure. Therefore, on a lot zoned RS20/RS40, there must be a single family house/manufactured home on the lot to be able to obtain an approved building permit for any accessory building or structure, generally.
There are principal uses, such as Agricultural Production, Crops and Agricultural Production, Crops, that once established on a bona fide farm, would allow accessory structures with an approved building permit, and no single family home required to be located on the site. The applicant provides documentation that the land is a bona fide farm. A link is below for this process, there is a $25 administrative fee associated with establishing the use with a simple zoning permit.
DocumentCenter/View/986/Farm-Use-Verification-Fillable-PDF