UBC: Uniform Building Code. A model code promulgated by the ICBO. The UBC has largely been displaced by the I-CODES®. (See also ICBO, I-CODES.)
U-FACTOR: The U-factor, or thermal transmittance, is a measure of the thermal conductivity for a building enclosure assembly (e.g., wall, floor, ceiling, roof) or a building component (e.g., window, door). Incorporating parallel and series conductive heat transfer principles and the R-VALUE or thermal conductivities of each component in the assembly, the U-factor can be calculated. The U-factor, when multiplied by the surface area and the indoor-outdoor temperature difference, predicts the amount of heat loss through the assembly, which means assemblies with low U-factors are more energy efficient. U-factors are typically expressed as (Btu/hr•ft2•F) or (W/m2•C). (See R-VALUE; THERMAL CONDUCTIVITY.)
UFFI: See UREA-FORMALDEHYDE INSULATION.
UL: Underwriter’s Laboratory. An independent testing agency.
ULTRA-VIOLET RADIATION (UV): Electro-magnetic radiation beyond the visible spectrum at its violet end. Invisible high-energy sunlight that degrades many organic materials.
UNDERLAYMENT: A material that is laid down as a substrate for the sprayed polyurethane foam to make the surface smooth or to give a specific rating for interior fire exposures.
UPLIFT: See WIND UPLIFT.
UREA-FORMALDEHYDE FOAM INSULATION (UFFI): Urea-formaldehyde foam insulation was developed as an improved means of insulating difficult-to-reach cavities in house walls. It is typically made at a construction site from a mixture of urea-formaldehyde resin, a foaming agent, and compressed air. When the mixture is injected into the wall, urea and formaldehyde unite and “cure” into an insulating foam plastic. The chemistry of UFFI and SPF are very different, as SPF contains no added formaldehyde.UV: An abbreviation for ultraviolet. (See also ULTRAVIOLET RADIATION)