SHCS vapor barier question
For those of you familiar with the SHCS design, I have a question regarding the vapor barrier that might go between the subsoil heat storage layer and the upper planting soil.
John C mentions putting such a vapor barrier under paths and walkways, to limit night heat loss in those areas. Simple enough. However in at least one of his youtube videos, he places such a barrier over the entire subsoil layer.
I am curious if anyone on this forum knows the finer details of where to use or not use this vapor barrier in a SHCS GH.