At a chilled loading bay in January, the door leaf runs with water before the first trailer of the day arrives. The insulation argument usually starts with a pair of quotations, one quoting R-value, one quoting a metric figure, and neither stating what the number covers. That missing line is the loading bay door U value, and whether you should calculate it has a straight answer. Calculate it when the door separates a conditioned space from the outside and stays closed long enough for that difference to pay. When either condition fails, the money belongs in seals and door speed instead.
A U value is steady physics, heat flow equals the number times area times temperature difference. The confusion sits in the quoting, because panel-center figures, whole-door test results and imperial R-values all wear the same clothes. We build dock doors and industrial doors in Hebei, and the declared U value rides on every drawing we ship. The factory inspection report travels with it, so the figure c