I'm trying to decide whether to use a damp proof membrane (DPM) at the base of my hut's timber post foundations. The larch posts are resting on 600mm x 600mm x 50mm concrete slabs and will be mostly protected from rain by the overhanging structure. Should I put a DPM under the base of the posts or not? Pros would be that DPM will prevent dampness from the ground travelling through the slab into the timber. Cons may be that the DPM will simply trap a layer of moisture at the base of the post encouraging rot.
Also wondering about a layer of DPM between the top of the larch posts and the C24 2'x6' treated horizontal ground beams?