I'm ready to start building my walls up from DPC but where the extension buts up to the existing building I need to know if I need to fit a vertical DPC to the existing wall in between the inner & outer leaf of where my new walls will be built. If I need this vertical DPC I then need to know how to fit it to the existing wall, i.e. do I cut a slot with a disk cutter and silicone it in?
If you disk out two slots and remove the brickwork, therefore effectively running the cavity continuously between the new building and the extension, you do not requie a DPC.
Building control are likely to require this anyhow to avoid a cold bridge.
If your plan was to make a single disc cut in the brickwork (what is currentyl the external skin, but will become an internal wall) you will require a vertical DCP to prevent penetrating damp. This method is not to be advised as there will be a cold bridge issue.
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