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suspended timber floor insulation question

 
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Hi,
I'm building a new house with green/natural skew. I plan to install both earthen and wooden floors on the ground level. The primary insulation is compacted 10'' foamed glass with geotextile below and above. I have a conceptual problem with the design of wooden floors. I've installed larch timber joists (2x7'') which are hanged on metal hangers fastened to ledger boards. On top of them will be softwood sub-flooring then hardwood flooring. So far I've planed to loose fill the voids between joists with expanded clay (house's walls are leca & clay). If I live on the desert I would be perfectly fine with it, but I don't There is no ventilation of the inside of the foundation (concrete wall with 2'' exterior XPS and 1'' interior expanded cork), so there will be some vapor rising from the ground which has only one way out - up to the floor.
Basically I could go three ways:
1. Do nothing, assuming that RH at the joists level won't be much higher then 80% and the wood won't deteriorate.
2. Install PE vapor barrier just beneath joists  then infill with expanded clay - the overall vapor migration will be lower, but it could go-up at the junction of the foundation wall and PE (I don't believe I could seal it well.
3. Infill with expanded clay & clay mixture which will work as a vapor retarder and moisture store - equilibrium moisture content of clay&leca is very low.
All above solutions are unconventional witch means I can't refer to good bad practices in my area.
There are a lot of other options to choose from, but I would like to choose from above with preference to the first one (least labor, no additional plastic), but I'm not sure if I'm not making gross mistake:) The water table in my area is rather high but no flooding records. The subsoil is fine sand with clay starting 6'-8' below grade.
Any thoughts / comments from you experienced and knowledgeable are welcomed.

 
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Location: Abkhazia · Cfa (humid subtropical)
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Lech, could you draw your ideas? (Nothing perfect, just good enough to get the idea.)

Here in Abkhazia with really high humidity and lots of rain, the living spaces is usually a little above the ground with plenty of ventilation below. When people cut that ventilation off, the floor rots. The downside is of course the lack of floor insulation.
I will have the same problem soon, when building a new house so I would like to understand your ideas.
 
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