Moved into new (to us, built in 1980) house 2 years ago. Installed an Airthings radon meter a year ago. Levels get up to 400 Bq/m3 when all the windows are closed. Finally had a radon mitigation system installed. Will hopefully get to much safer level below 100 Bq/m3.
would have loved to have bought a town house awhile back but it had radon issues and the association was not dealing with it. Since it was a shared foundation mitigating it would be sorta drawing it in from next door and so on. maybe it could be sealed enough in the one unit but the shared nature of the building made it feel like it would be just that much more annoying.