Hello all. First time post, need some advice please. I am building a smallish side extension to my freestanding garage, to use as a small workshop Found a builder and started on the workshop base, all seems ok. Talking to him last night about pouring the concrete base and the position of the DPM. He has built the dwarf wall with the plan to build a timer frame of this, infilled with hardcore and a sand blinding, all compressed down. I asked if the DPM would lap up against the old garage wall, he said no as this becomes an internal wall and you should not do that, He is the expert so I have to take his advice but it sounds wrong, anyone with any experience? Thanks.