- UNESCO landmark The structure is listed on UNESCO's registry of World Heritage Sites.
- u-shaped stairway Stairs which turn twice between successive floors, forming a U-shape.
- ube A medium shade of grayish purple.
- unaligned floor A floor level which is vertically offset from adjoining floor levels by at least half a meter.
- unbuilt Construction is never expected to occur.
- under construction An object is in the midst of being built and is not yet ready for use.
- under demolition Demolition has begun, and is actively progressing or expected to resume.
- under renovation A thorough upgrade is underway which affects the whole structure.
- underground building A building divided into regular floor spaces which does not have any usable floor space at or above ground level.
- underground mine A cavity or network of tunnels dug under the earth for extraction of minerals.
- underground station A below-ground space which provides access to a tunnel system, and which has no buildings over it.
- underwater building A fixed inhabitable building whose occupiable space is at least 90% underwater.
- underwear store Retail space specializing in bras, lingerie, intimate apparel, and other forms of underwear.
- unglazed window openings Open window apertures in a facade with no glass.
- uniform resource identifier A string of characters used to locate a particular piece of content on the Internet.
- uniform store A clothing store specializing in work uniforms.
- uninterrupted power supply Facilities for ensuring continued power in the case of a blackout in the normal supply.
- unisex restrooms Toilet facilities designated for use by any sex.
- unit One of multiple evenly divided sections of a building interior intended for a single user or group of related users.
- unit amenity Features common to individual units in a building.
- unitarian church A house of worship in the Unitarian faith.
- units Quantities of modular divisions within a structure for separate users.
- university An institution of research and high-level education.
- university Classroom space for higher education at an institution which grants bachelor's and higher degrees.
- university chapel A house of worship directly affiliated with a university.
- university office Working space for teachers and administrators in a college or university.
- unrenovated Space more than 5 years old which has not been significantly renovated in the past 5 years.
- unspecified tenancy design Built space designed flexibly so that there is little difference between accommodating one or more tenants.
- uranium mine A site where naturally occurring uranium ore is extracted from the earth.
- urea-formaldehyde foam Sprayed insulation consisting of urea-formaldehyde, a yellowish synthetic resin.
- urea-formaldehyde rigid panels Hard insulating panels made from polyurethane, a common plastic with exceptionally high insulation properties.
- urology Clinical space where doctors treat or advise patients for conditions of the urinary tract or male reproductive system.
- usable floor area The total area of all open interior spaces within an object.
- usage The general purpose intended for a structure, in whole or in part.
- usage begins Operation begins in at least one of the assigned uses of a structure or other object.
- usage event Events associated with the usage, management, or maintenance of an object..
- usage level The importance of a particular usage within a place.
- usage zone A part of a structure defined by the extent of one usage.
- user-generated website An internet page where content is supplied by multiple users of unknown or varying reliability.
- utilities Structures which serve the collection and distribution of energy and basic necessary materials.
- utility distribution Sites engaged in the spreading and transmission of utilities.
- utility vehicle depot A place for the storage of service or construction vehicles when not in use.