Some regions along the coast in East Hokkaido have peculiar climates, with dense fog in summer and abundant sunshine in winter. The purpose of this paper is to propose how to effectively use a "sunroom" during summer and winter in these regions. Air temperature and humidity conditions were measured in both summer and winter within two detached houses in these regions containing a "sunroom". From these measurements, the following knowledge was acquired: 1) In summer, a large sunroom provides good environmental temperature conditions for a living room connected with it during the dense fog season. 2) In the case of a detached house built with a sunroom, it could be predicted that the heat loss through glazing doors situated between the living room and the sunroom greatly decreases in winter.
