My Neighbour has consented to me Building a Party Wall Astride the Boundary. Where exactly should the Wall be Positioned?

Question

My neighbour has consented to a party wall astride the boundary to enable us to construct a garden extension.  The wall will be a standard brick outer leaf, 100 mm insulated cavity with a block inner leaf.

Is there a recognised specification on how far over the boundary the party wall should be built?  Specifically, should the boundary line run down the middle of the cavity or down the middle of the outer brick leaf?

Answer

The new wall should ideally be centered on the boundary line.

Sometimes it suits a Building owner to keep it slightly more on their side when it is replacing and existing garden wall and they do not want to interfere with the Adjoining Owner’s paving etc.