Building insulation

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Building insulation refers broadly to any object in a building used as insulation for any purpose. The most common one is thermal insulation, which is an important factor to archive thermal comfort for its occupants. Insulation reduces unwanted heat loss or gain and can decrease the energy demand of heating and cooling systems. In a narrow sense insulation can just refer to the insulation materials employed to slow heat loss, such as glass wool, polystyrene ETC. The effectiveness of insulation is commonly evaluated by its R-value. 

(http://en.wikipedia.org/wiki/Building_insulation)

As a rule, insulating homes is important in any climate and, typically, the more insulation (i.e., the higher the R-value) the better. Properly installed, insulation decreases unwanted thermal gains or losses through the envelope throughout the year.

In general, insulating the attic or roof should be the first priority since the most extreme boundary conditions or temperature differences typically occur at or around these areas. However, other hidden areas need to be insulated by home builders and contractors. These spaces include finished and unfinished attics, all exterior walls including those between living spaces, and floors above cold spaces, even slab floors built directly on the ground.