I have four cats that have a bathroom in the basement. The house i rent is a side by side. Concrete wall and wood door separate the basement. My previous neighbor had two cats and when the new neighbor moved in they noticed a urine smell in their kitchen and contacted me. As a good neighbor I have used vinegar, bleach, peroxide and KILTz with the neighbors still complaining of a smell when it is hot/humid out or turn their heat on. On my side I have never smelled urine unless it happens. I smell the litter more then anything.
but considering the concrete wall is three inches thick I was wondering if both side would need to be treated?