Understanding R Value and Heat Loss
How much energy does my home use for heating and cooling? Once you’ve plugged all the air leaks, this question is answered by the R-value. But each area of outward facing surface of your home has its own R-value. There’s one for the ceiling, one for the walls, one for the floors, one for each window, one for each door, etc. The greatest heat loss is from areas with low R-values, although the ceiling gets extra attention because heat rises in the winter and attics and roofs get very hot in the summer.
Remember “This Old House”? They produced a great video explaining R-value.