It is very basic principle and rule of nature that molecules move from hot areas to cool one. And hot air blows and is replaced by the cold air always.Hence, if the area you are living is surrounded by cool environment the heat you have generated to keep your room or home warm will move in the direction of cold area and will replace it.
In a home it is usually done through various major ways like doors, windows chimneys and many more, but if all of these are sealed there are still some hidden ways that heat can find to escape, these are known as lofts.
These lofts are most of the time found in roof. So in loft insulation it becomes so difficult for the hot energy or heat to escape from it as it does not allow any heat to pass and become resistant against its passage. This is done with the help of a loft material which is filled with some air thing called air pockets.
These air pockets reduce the U value of the loft present anywhere in the roof. This U is actually the value that calculated to know that how instantly and in what range a roof can loose the energy. The mathematical survey calculation is ranged between 2.3 to 0.16 W/m2 k, which means that it will only allow up to five percent of heat loss and remaining ninety five will be restricted.
On the other hand some professionals use R-value which on contrary give inverse of the calculations made by the U value’s calculated. It also has a constant value of approximately six to seven km2/W. these lofts are necessarily recommended by the governments and NIA recommendations and the values that are to be used here are R-values.none