I don't know what the laws are where you are, but where I live you are not allowed to channel water to someone else's property. It must exit your own property to the street. I agree with Yardvaark. It sounds like you need to research where the city planners designed the water to go and find out why its not going there. Its not hard to find that info. The city should be able to give you the development plan for your subdivision. Our city worked with us to help us solve the problem we had. I was told that just after the subdivision was built some neighbors further up the hill from us had similar issues to you. The city had to come in and build a storm drain through at least 2 of the lots to solve the issue for them. If you were not having these issues before your neighbor built his pool and garage then it sounds like you need to bring the issue up and demand it be solved. If it had happened to us and the city and homeowner weren't helpful in solving the problem we'd be suing both of them for not addressing the issue of drainage and recouping the cost of having to pump all that water out. In my son's old neighborhood the one house on the corner that was the lowest and kept getting flooded year after year was finally purchased by the city, torn down and a small park sits there now. But it took a long time for that to happen. I don't know for a fact, but I suspect law suits were involved. - In the link below I show how we solved our problem. But we really didn't have much issue with neighbors' lots draining into ours it was that our lot wasn't graded correctly in the first place and the water had no outlet to exit our property. Good Luck and please report back what happens. Here is a link that might be useful: Back yard drainage

A potential avenue to research would be the installation of a strategically placed rain garden or two. You can install catch basins below your gutter downspouts and pipe them directly into your rain garden. Besides helping with your water issue there are many other benefits to creating a rain garden. For example: Rain and melting snow (if you live in MN like myself) runs off your roof, driveway and even your lawn, directly flowing to the street and inevitably down the storm drains. All of this runoff, when untreated, carries pollutants like oil, salt, fertilizer and pesticides that are being directed right into our rivers, lakes and streams. This is causing major issues with our fresh water! Your rain garden(s) will capture all that runoff and hold thousands of gallons of rainwater that can be used to feed your beautiful garden and surrounding plants while also infiltrating water deep into the ground helping to maintain your water table. Plants, mulch and soil effectively break up the pollutants and make them non harmful to us. Lastly, a rain garden is not only beautiful, it creates a habitat for birds and beneficial insects and not to mention it makes a great statement for your appreciation of nature and humanity,

The guy that cut out the Sheetrock should have found the vapor barrier when he removed the base boards. Any experienced floor installer/repair guy should have noticed it missing also. The way I do it is lay the vapor barrier out and use thumb tacks to hold the ends approx 6" up on the walls. Small bead of silicone on the seams approx 6" back from the edges then tape the seam. Next the underlayment will go down (in your case foam). Next the flooring. To finish I take a sample of the base board/trim and hold it in place against the wall and use a Sharpie to trace the top edge onto the vapor barrier. Then trim the vapor barrier 1/2 to 3/4" below the line. It leaves 3 1/2 to 5 1/2" of vapor barrier up the wall (depending on trim width). But I have never had to go back to repair damage due to sweating slab syndrome or vapor problems.

We had to address similar issues with our property. One of the problems was a neighbor who had "built up" his property over the years. This is actually illegal, in that, "you are not allowed to do anything to your property that causes a problem for someone else" (i.e., water runoff). But it was also a priority to maintain the friendship. We used a commercial landscaper who specialized in drainage and irrigation. It was an expensive project, and most of it is unseen, but it solved all the runoff, erosion and water seepage in two corners of the foundation. {We had bids from at least 6 residential landscapers, but none of them really knew how to solve the problem.}