Suppose there is a wall and half of its area has R-value 10, and the other half has R-value 20. Is the total R-value of the wall 15? In other words, can R-values be averaged weighted by area?

Please justify your answer with math. R-value is defined as follows on page 454 of the *2020 Residential Code of NY State*.

> R-VALUE (THERMAL RESISTANCE). The inverse of the time rate of heat
> flow through a body from one of its bounding surfaces to the other
> surface for a unit temperature difference between the two surfaces,
> under steady state conditions, per unit area (h • ft2 • °F/Btu) [(m2 •
> K)/W].