I want to add an extension, but my neighbour's extension is on my property

Questioner

I want to have an extension built on my backyard. My neighbors already have an extension from the new construction and their side wall is 18 cm on my yard. My neighbor does not allow me to build anything on/against it in any way to place my extension. He makes it very difficult for me to build anything. He does not even want to shorten a piece of gutter to the property line so that I can neatly connect to his wall. Can he refuse everything if I have officially had a building plan drawn up by an architect in accordance with building regulations? He is not disadvantaged by this and everything is neatly finished as it should be.

Lawyer

In principle, you do not have to tolerate your neighbour building over your property unless you have granted each other the rights to do so by deed. Does the wall of the extension function as a kind of shared wall/partition wall between two properties? Then you may certainly build up to half of the thickness. However, you may also use an unlawful overbuilding to negotiate your wishes, because you may demand its demolition within 20 years.

Questioner

Dear Mrs. Ferwerda, Thank you for your response to my question. This is a 1.2m piece of the neighbour's private wall. It is a new-build house from 2019 and my neighbour opted for an extension during the new construction. I could not do that because I was allocated the house late. The deed states that the side wall of the extension goes over the property line if the neighbours do not take an extension. So it is a private wall of the neighbour, but on my land. So he demands that I build completely independently of him. But it also has to be waterproof and windproof between the walls at the same time. But then it becomes a very strange extension.

Lawyer

That does not make it a shared wall. In principle, you may not build on without permission. However, it is also the case that your neighbours must have an interest in refusing to give permission. In those cases, it may be that you are allowed to build on after all. This will have to be explained to your neighbours properly, referring to the law and case law of comparable cases.