The study was initiated to evaluate effects of automotive emissions from attached garages on the indoor environment in Canadian single-detached houses and the impact on occupants' health. This work consisted of testing a total of 25 houses in the Ottawa area to characterize the extent of leakage between the attached garages and houses. The selected houses were from various age groups, styles and types of attached garages. The study found that most of the air leaks from the garage were found to be leading into the basement.