Insulation is a very important parameter to consider. In fact, before one considers any passive or active technique, the building must be well insulated to reduce thermal loads. The most important element of the building to insulate is the roof. This is very important for horizontal concrete roofs, which, during summertime, when the sun is higher in the sky, receive a considerable amount of radiation, which can increase the roof temperature considerably (Florides et al., 2000).

The way to account for insulation is by using Eq. (6.34), presented in Section 6.1.5, by incorporating the appropriate thickness and k value for the insulation used in a structure.

Example 6.4

Consider the wall construction of Example 6.2 with the addition of 2.5 cm expanded polystyrene insulation. Estimate the new U value of the insulated wall construction.


The resistance value of the wall without insulation is 1.18 m2-°C/W. From Table A5.4 in Appendix 5, the thermal conductivity of expanded polystyrene is 0.041 W/m-°C. Therefore, its resistance is 0.025/0.041 = 0.610 m2-°C/W. Therefore, the total resistance of the insulated wall construction is 1.18 + 0.610 = 1.79 m2-°C/W. Finally, the U value = 1/1.79 = 0.559 W/m2-°C.

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