Slab-on-Grade vs. Pier Foundation for Conditioned Shed
Planning to construct a new 10×12 shed that will be finished, conditioned and utilized as a permanent work from home office. Heating and cooling will be via a ductless mini-split, and supplemented with a pellet stove. I am currently working through foundation details and debating between a slab-on-grade or pier construction tradeoffs. The site is level, and fairly-well drained, but Pennsylvania can get and stay wet.
Option 1: Slab on Grade: I would install a layer of rigid foam below the slab (similar to GBA detail sheets), but I am concerned that the slab floor would still be very cold throughout the winter (radiant heat sink?). I live in Pennsylvania so winters can get quite cold. Would it be best to also insulate on top of the slab? Possibly with a 2×6 framed floor? Temperature is important as this is to be an office (mostly stationary) work space.
Option 2: Pier Construction: This option is attractive in that thermal bridging would be greatly reduced. I could sheath the under-side with rigid foam (under the joists) and then a layer of pressure-treated plywood below the foam. The joist bays could then also be filled with rockwool. My concerns are a) moisture from below (rotting the plywood over time – PA is very wet usually) and 2) rodents chewing from below to make nice cozy homes in the joist bays.
I like the slab option the best for durability, but the space needs to be comfortable.
Thanks in advance for any advice on best route to take.
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