party wall advice please

[muso58]

Hi im about to build a small extension at the rear of a terraced property .The neighbours either side have already built 3 metre deep single storey . extensions
Im intending to build my single storey extension between theirs .My question is can i use the party walls as my walls .they are on the boundary of my property .The neighbours dont mind me doing this ,but im not sure if they are up to modern spec .ie 1 metre deep foundations .
Are council inspectors likely to raise this as an issue ,or will it be the case that as these are existing walls they will be deemed suitable for the new build.
Thanks in advance

 

[geraldthehamster]

Try posting this in the Building forum.

Cheers
Richard

 

[wessex101]

Not sure what you mean by built "on the boundary". Either the walls are built up to the boundary or astride it. Either way, if the neighbours agree the walls can become party walls by enclosure or are already party walls. Probably worth getting written permission for the former though to be on the safe side.

Main issue I can see is getting the existing walls to comply with sound transmission as they will change from external walls to separating walls. You'll probably need acoustic drylining on your side of wall to upgrade, and possibly something at roof level for sound transmission and fire resistance.

As you said the walls will need to be structurally adequate but not necessarily full depth foundations and you will need to demonstrate how you will weatherproof the junction between the new and existing roof. Overall should be relatively straight forward.