I live in Pennsylvania and my neighbor is building an add-on to their house that invades my backyard privacy and probably devalues my home, what can I do?
Your first step is to check to see if your neighbor is required to have permits for the add-on, and if so, whether he has pulled the permits. Some municipalities limit how a house can be extended for the very reasons you stating. If your neighbor has not pulled the proper permits, the city can intervene and stop the construction. Similarly, if you have a homeowners association, they may limit how a homeowner can add to his home, and may have an approval process for additions. You can contact your HOA to see what your options are.
If your neighbor has the correct permits, and an HOA cannot intervene, your only option may be to file a lawsuit against him. The most obvious claim is a “loss of quiet enjoyment.” Every person has a right to enjoy his property without being unreasonably bothered by his neighbors or other nuisances. Unfortunately, this can be a very difficult claim to make, both because your neighbor also has the right of quiet enjoyment (which means he can reasonably improve his home) and because you have to prove that your neighbor’s actions are infringing on your right to quiet enjoyment based on your reasonable expectations.
If you feel that legal action is necessary, you should contact a property attorney who can consider all of the facts and advise you as to your best options.