UL - Underwriters Laboratories, Inc.

UL label -  Label displayed on packaging to indicate the level of fire and/or wind resistance of asphalt roofing.

Underlayment - Asphalt saturated felt used beneath roofing to provide additional protection for the deck.

ULTRAVIOLET - The invisible rays of the spectrum of light which are at its violet end. Sometimes abbreviated U.V.

UPRIGHTS - Vertical members supporting the sides of a trench.

U-VALUE - A measure of air-to-heat transmission (loss or gain) due to the thermal conductance and the difference in indoor and outdoor temperatures. As the U-value decreases, so does the amount of heat that is transferred through the glazing material. The lower the U-value, the more restrictive the fenestration product is to heat transfer. Reciprocal of R-value.

ULTRAVIOLET - The invisible rays of the spectrum which are at its violet end. Sometimes abbreviated U.V.