GAC93

Hi, im currently in the process of purchasing a semi detached property and hoping to put an extension on the back. My concern is that the neighbour also has a rear extension but they have a window located in the centre of the side of the extension at the top which appears to be frosted glass and so is there for light purposes rather than for viewing. the window is around 1 metre in length and approx a ft in depth. The window is facing our garden and is just behind the property line, and so if we also do an extension we will likely block the light to the window, especially as our plans is to do a two story extension. ive attached a photo. if anyone has any advice on this it would be appreciated. Thanks.