Extensions

Building next to neighbours extension....options?

Anonymous user 09/03/2024 - 3.04 PM

Hello! We are planning a single storey rear 3 x 5 m extension to our 1930 terraced house. Having got a few quotes from builders I'm a little confused by the advice on how we build next to our neighbours existing extension. They have the exact shape and size extension we'd like to build so we would essentially copying the structure and extending across the back of our house at the same height and depth. The neighbours extension appears to be built up to the boundary line so they own the wall entirely. Here are the options I've been presented: 1) Build off the neighbours extension with a nib wall. This options saves both money, time and space but would involve the neighbour agreeing to use of their structure. I can also see potential issues with a) future sale and ownership of wall b) if they decide to rebuild their extension and knock the wall down c) issues of maintenance or subsidence. 2) Build flush to the wall and create a party wall. This option is most unclear, can we build flush and continue the fascia and roof without an air gap? Could we double the thickness of the wall and create a similar party wall agreement as our current internal walls? How would this affect foundations? 3) Leave a 200mm air gap and build an independent wall. This is the easiest option in terms of agreements with neighbour but would cost more, loose interior space and cost more. We are also concerned about damp, debris and pests from nearby river. I'm interested in hearing thoughts on the options and any solves from previous projects. Thanks in advance! Chris