The purpose of this study is to find the infiltration of detached houses, for energy consumption analyses. The pressurization and depressurization method is used to determine infiltration. Blower door tests are expressed in terms of ACH 50, which stands for the hourly air change rate at 50 Pa of fan pressure. The ACH 50 of existing Detached Houses ranges from 5 to 50. Air infiltration is related to construction year and accuracy, maintenance conditions, and so on. When estimating the infiltration of random detached houses, the year used can be the base value of the infiltration rate from 0.25 to 2.0 times/h. The maintenance conditions, construction accuracy and repair affect the air infiltration 0 to 0.5 times/h, 0 to 0.3 times/h, 0 to 1 times/h, respectively.