As this case illustrates, incorrect flashing installation is often the cause of leaks on roofs with chimneys. The company that put in the original flashing on this house did not do it correctly, which left an expansion and contraction process that permitted filtration when it rained. We remedied the situation by removing the old flashing system and reinstalling a new one with the proper waterproofing products that would allow it to expand and contract with the seasons, and maintain a tight seal against water filtration.