Can my neghbor legally build a back-porch that causes rain water to dump on my property?

Most areas has an easement for utilities along the edges of the property. If his porch roof is actually shedding rain water onto the fence on the line, it is probably violating that easement. Contact whoever issues building permits in your area and ask about the rules.

Most easements are more like five feet or more, meaning that you can't build within five feet of the property line. Some places are as much as 12 feet.

If he is within the easement requirements, it would depend on the local laws. Here in TN, it would be your problem to deal with the water. He could point all of his downspouts straight at your property and you would have to divert it to the next guy.

Another option would be to build up the top of the brick fence, if it is a thick one, with a sloped cap pointing back at his house. The water will still leach through the wall, but not before it makes a lake on his side. He should have gutters on it anyway.

EDIT: building a structure is not considered altering the water flow. Building up the grade of the land or digging trenches is altering the water flow.

Altering existing water flow and runoff is not generally allowed and would require special approval by your city planning commission. Your neighbor's request for a building permit should trigger this question by the city. You cannot create a problem on someone else's property to fix one on yours - very simple. Before getting lawyers involved, why don't you try to talk with him. Tell him your concerns and ask him what his plans are for routing the water away from your property. If he refuses to cooperate with you or becomes snarky, contact the city and find out what the rules are for your municipality exactly as far as altering the water flow/run off from one's property to another. Once the city gets wind of it, they may come out and flag his project until he gets all the details squared away. Good luck -

Before going to any lawyer or any legal action. Why not talk to your neighbor. Im sure that they may also be disturbed when the same thing is done to them or they maybe unaware about the effect of what they did. If that will work, not only you win your neighbors trust, you also save the cost of filing legal suit for petty things that should be resolved between you and your neighbor in the first place.

Yes you can. Sue for Private Nuissance and seek an Injunction. Go see an attorney about this. It's a pretty common thing.

Ask them to stop or modify the design...that's the good neighbor way...otherwise you may have to sue them.

Another way is to contact the local building inpectors office and inform them..if it's a certain size they need a permit and needs to be inspected.

In order to do construction like this he most likely needed permits. in order to get these permits he most likely needed the approval of all neighbors in the vicinity. Check with the local officials to see if he has gotten the permits and if he has, file an objection.

first of all,he is suppose to stay 6 inchs from the line with any structer.i would call the building insprcter,and let him know.the guy probily does not have a permit for it,the inspecter take care of that for you.

Most states prohibit the altering of water flow.

File an a request in the court for an injunction.