Thermal Conductivity
The k-value (thermal conductivity) represents the amount of heat
that flows through 1 square foot of a homogeneous material 1 inch thick in 1 hour for each degree of temperature difference between the inside and the outside temperatures.
To illustrate, we shall use an example from the ASHRAE data shown in Tables 3-1 and 3-2. You will note that the k-value for face brick listed in Table 3-1 is 9.0. In other words, 9.0 Btu of heat can pass through 1 ft2 of 1-in-thick face brick each hour. The ther- mal resistance (R-value) of this same 1-in-thick face brick is the reciprocal of its k-value:
Remember, this is the thermal resistance for a 1-in-thick face brick. Because the masonry wall in Table 3-2 contains a 4-in thickness of face brick, you will have to multiply the R-value (0.11) of the 1-in-thick face brick by 4 (4 in) to obtain the R-value (0.44) for the larger (4-in) section.