46% of apartment residents in smoke-free units still breathe secondhand smoke from neighbors through shared walls, and sealing efforts are proven futile

The American Lung Association reports that approximately 46% of U.S. multiunit housing residents who maintain smoke-free rules in their own homes — roughly 29 million people — still experience secondhand smoke infiltration from neighboring units. Smoke travels through shared walls via electrical outlets, plumbing chases, gaps around pipes, HVAC ductwork, and pressure differentials created when bathroom fans, kitchen exhausts, or clothes dryers create negative pressure in one unit and pull air from adjacent units. The infiltration pathways are numerous and diffuse. The health impact is not hypothetical. Secondhand smoke contains over 7,000 chemicals, at least 70 of which are known carcinogens. The Surgeon General has concluded there is no safe level of exposure. For the 29 million people affected, this means chronic low-level exposure to carcinogens, particulate matter, and respiratory irritants in the one place they should be able to control — their own home. Children, elderly residents, and people with asthma or COPD are disproportionately harmed. And because multiunit housing skews lower-income, the people least able to move are most likely to be exposed. A renter who complains to their landlord about smoke infiltration has almost no recourse in most jurisdictions — there is no federal law prohibiting smoking in private residences, and only a handful of cities have adopted smokefree multiunit housing ordinances that apply to existing buildings. This problem persists because building codes do not require air-sealing between dwelling units to the standard needed to prevent smoke transfer. Retrofitting air barriers in existing buildings is extremely expensive and requires access to wall cavities, ceiling plenums, and utility penetrations. Research has shown that residents' own efforts to seal cracks, use air purifiers, or increase ventilation are futile at eliminating exposure — the infiltration pathways are too numerous and too small to individually address. The fundamental issue is that apartment buildings are designed for structural separation between units, not air separation, and no one is responsible for the air quality consequences of that design gap.