The main factors are: wind loads, building orientation, solar radiation, shading.

Windy sites have an unfavourable effect on the thermal energy requirement in the colder part of the year, because the building cools down more quickly due to the flow of cold air. With ordinary buildings this makes a considerable difference, but even in highly energy-efficient buildings the requirement can be 2–3 kWh/m²a higher. In windy areas, a (natural or built) windbreak can significantly reduce air flow and thus save thermal energy.