The total basement heat loss in residential structures is comprised of losses from the floor header, the above-grade portion of the foundation wall, belowgrade portion and basement slab. The loss of heat,through each of these components is governed mainly by the laws of conduction - temperature difference, resistance, exposed area - however, the application of these laws to analyze below-grade wall loss is made extremely difficult because of the lack of uniformity and stability of conditions surrounding these walls.

The layers of insulation, concrete, adjacent backfill, undisturbed ground, ice and snow, all have different heat conduction properties which give rise to potentially complex two- and three-dimensional heat flow from the basement to the atmosphere or to ground water. Furthermore, the significant mass of earth in the path of the heat flow introduces a thermal storage effect, and the moisture in that ground provides an additional heat storage mechanism via the formation of ground frost. Finally, the earth somewhat below the basement floor is in itself a quasi-independent heat sink for the lower portion of the wall, with its temperature held steady by virtue of its large mass and circulating ground water. All of these factors are believed to be of importance in determining the heat loss characteristics of the basement wall from ground level to the slab. Together they have defeated all attempts of mathematical analysis and computer-based modelling, so that this engineering method for estimating annual basement heat loss and insulation performance is offered strictly as a useful, unquestioning "fit" against monitored cold-country realities.