Concentrations of many volatile organic compounds (VOCS) are often higher inside residences than outdoors as a result of sources or activities within the residences. These sources can be located directly in the living space of the home or in areas associated with the home such as an attached garage, basement, or common apartment hallway. To characterize the contributions front these areas to indoor residential concentrations, VOC concentrations were measured inside, outside, and, if present, in the attached garage, basement, or common hallway of an apartment of 55 residences in the Boston area, most over two seasons, as part of the Boston Exposure Assessment in Microenvironments (BEAM) Study. Of the 55 residences in the study, 11 had attached garages and basements, 24 had only basements, 10 other residences had common apartment hallways, and the remaining 10 were treated as single compartment residences. Concentrations in the garage were LIP to 5-10 times higher at the median than indoor concentrations for mobile source pollutants including benzene, toluene, ethylbenzene, and xylenes. Basement/indoor concentration ratios were significantly > 1 for methylene chloride, ethylbenzene, m,p-xylene, and o-xylene, and summer ratios tended to be higher than winter ratios. Approximately, 20-40% of the indoor concentration for compounds associated with gasoline sources, such as methyl t-butyl ether (MTBE), benzene, toluene, ethylbenzene, and xylenes, can be attributed to all attached garage at the residence, with garages laterally attached to the first floor of the home having a larger impact. At the median, basements contributed to approximately 10-20% of the estimated indoor concentrations. For apartments, approximately 5-10% of the estimated indoor concentrations confer with air front the hallway. Contributions of these secondary zones to concentrations in the living area of a home were calculated using concentration and airflow estimates. Our findings illustrate the potential significance of these non-living spaces from in exposure perspective and suggest potentially effective mitigation measures. (C) 2007 Elsevier Ltd. All rights reserved.