So we bought a detached house, and it's my own fault for not checking. So the side of my house is on the boundary. There is perhaps a 4 ft gap between our house and their garage. Sometime before we moved in they covered this over with corrugated plastic and put a proper sealed door at the front and extended a wall down the side of the house. They use this area all the time, more often then their actual front door, and I'm constantly hear them banging and crashing down the side of my house. I bought a detached house for a reason, they are noisier than any of my neighbours when I have lived in attached homes. They told me it's not attached, but aside from breaking into their house I have no proof. I can hear them clearly shutting the door as I do when DP shuts (stiff) garage door! Would they need to have planning permission for this, and if they have used my house to support the structure what can I do about it. I just find it so irritating as they are up at the crack of dawn and I wake me up!
If they have attached anything to your property, they would need your permission. they would also need planning permission, as permitted development rights are only for development within the boundaries of a property - by attaching to your property, they have breached that. Are the properties fairly new/part of modern development? If so it is worth checking with the Council to see if the houses actually have permitted development rights, as these can sometimes be removed when larger developments are given planning permission. Not an expert, but they may also need a Party Wall Agreement.
What if it was done prior to us moving in? Of course the vendors never said a word about it. It's a 70's house, so I don't suppose they have had the permitted development rights removed. I'm guessing they have attached to our house, I would have to put a ladder of their drive in order to look down at it because our house is forward of theirs.
Sound does carry through the space between houses though. You'd need to be quite a way away from each other not to hear anything at all from your neighbours.
Wouldn't a quiet word with them be better in the first instance? That and perhaps, have them come and stand in your house while someone crashes around in the way you describe, so they can see how loud it is for you?