It is likely that a close neighbor will have similar soil, but differences in home construction can have enough of an impact on radon exposure that you can't qu

It is likely that a close neighbor will have similar soil, but differences in home construction can have enough of an impact on radon exposure that you can't quite treat a neighbor's level as an indicator as your own. Think of it like groundwater, if the water table is high enough then both of you have an equivalent risk of seepage and leaking into your cellar, but how those cellars or foundation slabs are constructed also has a big impact. If this is a cookie-cutter suburban development where all the houses were built using the same materials and same basic plan then they will probably have similar radon levels, but if houses were built at different times or by different companies at the same time all bets are off.