Heat Loss Through Roof
The table below shows a breakdown of the heat lost through the various surfaces of a 1970's Wimpey house. It shows
 Heat loss without insulation. (As it was when the house was first built).
 Heat loss with insulation installed.
 The heat loss expressed as a percentage of the total.
 The annual cost of the heat loss.
With respect to the roof the addition of loft insulation was calculated to  Reduce the heat loss by 97%
 Reduce costs by an estimated £381 per annum
 Heat Loss without insulation. (W/K)  Approximate Annual Cost. (£)  Heat Loss with Insulation. (W/K)  Approximate annual cost. (£)  Annual Saving. (£)  Roof  297 (45%)  395  10 (5%)  14  381  Walls  177 (27%)  237  69 (34%)  93  144  Doors and Windows  133 (20%)  176  86 (42%)  115  61  Floor  52 (8%)  70  40 (20%)  55  15   659  878  205  273  601

The calculations for heat loss per degree difference between inside and outside temperature gave a figure of 10.44W. Using this figure the calculated heat loss for a cold winters day would be as follows
Heat loss through ceiling with insulation = 10.44W/K Outside temperature = 1C Indoor temperature = 18C Temperature difference = 19C Heat loss = 10.44x19 = 198W
This is 1% of the boilers output.
For comparison, if there were no insulation, the heat loss would be
Heat loss through ceiling without insulation = 296.84W/K
Heat loss = 296.84 x 19 = 5640W
This is 35% of the boilers output.
And finally, the heat lost through an uninsulated loft hatch will be
Heat loss = 2.46 x 19 = 47W 