I am a homeowner living in a house just 5 feet from the next house, which is a rental. The area between the houses is a concrete walkway. Now the end of the walkway has collapsed after the neighbor's kid and their friends jumped and stomped on it after discovering a small hole in the pavement. Now there's a hole there that's 3 feet wide, and 1.5 feet deep. I contacted the landlord who basically called me a liar when I told him what I saw happen, and then I called the police to file a report about the damage in case it becomes a legal issue. He then contacted the health department who came out and looked at it. He said that it looks like the soil beneath the concrete was undermined because of water coming off my roof. However, my roof is much longer than the eroded area and there are no valleys on that part of my roof (the corner) to cause rainwater to concentrate on that area, and no erosion is taking place anywhere else. Now, I have noticed that the neighbor's backyard is on a slight incline toward this area, and where the backyard ends, so does the sloping, and the concrete area begins. That's also right where the undermined area begins, and it crosses his property line over to mine and ends at the foundation of my house, which is now exposed. That's about all the information I can think of to give you. My question is: Would water coming off my roof be enough to cause what I've described? Would water running off my neighbor's backyard cause it? (BTW, the slope in my neighbor's yard is 26' long, and the elevation drop from top to bottom is 2.5', just so you know how big it is). Where the erosion is sort of resembles a sinkhole. I can't think of anything that could cause it except water runoff, but I wanted to ask the experts here for their opinions. You're more knowledgable about this stuff than me!