New cavity wall abutting an existing drystone wall

[Bemak]

just a quick query on a detail I want to ensure is correct. i'm planning to construct a cavity wall extension to the side of an existing two-storey farmhouse. the new extension will replace an old stone extension and we've yet to determine if the stone extension was keyed into the stone of the main house. In any case - I was wondering how best to detail the junction between the new blockwork and existing stonework to prevent any water in the stone wall from getting into the inner leaf (as per the crude diagram below). Is a vertical DPC the best bet or is there a better way of doing it?

 

 

 

[kandgmitchell]

You'll need a vertical dpc where the new inner leaf meets the stone wall. However, this is one of those situations where you just have to live with the potential ingress into what is now the internal stone wall. Just think that wall was exposed and how much damp came through it? Is the situation going to be any worse than if that blue arrow on the right came straight across the "existing stone wall"? With an existing cavity wall you can cut in a dpc or chop out a bit of the old outer leaf but not in a stone wall.