1. A measure of how well a building element transfers heat, with smaller values corresponding to better insulation and hence less heat loss; it is the rate of energy loss per unit area per degree difference in temperature, and is equal to the inverse of the R value
   "a solid brick wall has a U value of about 2, similar to double glazing; well-insulated modern buildings should have walls with a U value less than 0.3"; "a solid brick wall has an overall heat transfer coefficient of about 2, similar to double glazing; well-insulated modern buildings should have walls with a U value less than 0.3";
   - overall heat transfer coefficient

Derived forms: U values

Encyclopedia: U value