Direct Solar Heat Gain (hereafter DSHG)is defined as the method to decrease heating load by using solar radiation from large south faced windows. Researches for DSHG have been conducted for many years. Although, there is a few research that analyze surroundings obstacles such as buildings, woods etc. It indicates that calculated cooling loads are bigger than an actual value and heating loads are smaller than actual value. Then, Architects and engineer should consider the risks on those research results especially in winter season. Recently, there are some researches for DSHG with woods and city form around a building. However, there are various cases in actual situations. In this research, we developed a method to analyze the effects of DSHG on heating load for detached housing in actual situation by using GIS data. Recently, the services of GIS data have been developing. Google provides GIS data with Google map and Google earth. Japanese government and Japanese prefectural government also provide free (open) GIS data. The data include elevation of a site, shape of buildings, address, number of stories, name, structure, total floor area, etc. Users can use the data with confidentiality agreement. The outline of the surrounding environment (form) is able to be made by using such GIS data. The climate data that is combined with the surrounding environment is able to be used for the analysis of DSHG. In this paper, we report 1st; criteria to judge whether DSHG should be used or not by using GIS data, 2nd; the effect of DSHG under the situation where solar radiation is decreased by surrounding obstacles around building, 3rd; the chart which express the relationship between DSHG effect and interior design. (C) 2015 The Authors. Published by Elsevier Ltd.