U-Value is the calculated thermal efficiency of a building.
U-Value is defined as the amount of heat / energy (measured in watts) flowing through 1m2 of an element (aka; 1m2 of a wall, roof, floor or window) when the temperature difference between the two faces of the element (ie; the difference between the outside air temp and inside airtemp) is 1 degree Kelvin (W/m2K).
The lower the U-Value the less heat flows through the element and hence the more energy efficient it is.
The Specific Heat Loss Characteristic of a house is a summation of all of the heat flowing through all of the elements plus an allowance for the amount of heat lost by way of air infiltration and ventilation.
How Building Structure Effects Heating Bills
Block houses are thermally heavy and take many hours to properly heat up. Once heated the inferior U-value of the structure means a high amount of energy is required to maintain the desired temperature / comfort level.
Timber Frame houses however are thermally lightweight and therefore heat up much faster, thus using less energy and rendering them ideally suited to todays lifestyle of intermittent and variable occupancy. In addition to this the superior U-value provided by the timber frame design means a far lower level of energy is required to maintain the desired temperature / comfort level, and thus far less needless energy is used, saving the environment from unnecessary CO2 emissions and saving you an average of 33% off your heating bills.