radon in attached houses 5

https://zulu-wiki.win/index.php/Understanding_the_Pennsylvania_Radon_Action_Level_for_Homeowners_in_York

Radon in attached houses can be a hidden issue, since the gas moves easily through shared walls and floors from the ground below. If a neighbor's home has high levels, it doesn't automatically mean yours does, but it's a good reason to test your own lowest living space. Unlike standalone homes, attached houses might have less natural ventilation in certain areas, so sealing cracks and considering mitigation can help keep your air safer.