We are building a 700sq ft fabric yurt in the adirondacks. Yurts are poorly insulated, r-10 for walls and ceiling. We will use this only on weekends and don't want to do concrete. We will have a small wood stove but love the idea of using radiant heat as main source of heat. On-grid and planning on a simple 30' platform for the yurt of 4 x 6 joists with thermax insulation. Can I use a warmboard product on top of the joists or run the pex through the joists over a foiled insulation instead of the thermax. Cost is important.