Reading floor builds with interest as my turn will be coming up shortly.
I like the idea of gluing all layers, polyiso to metal floor with plywood base glued to polyiso.
This is certainly the strongest, most rigid and least likely to squeak designs.
I like it a lot.
Can anyone think of a reason why the base floor would need to be removed ?
Molding due to water leaks? Need to access buried utilities, electrical, plumbing ? best not to bury that of course.
Road accident requiring removal of damaged floor to be replaced when restoring inside?
I strive to have as much access as possible for maintenance, repairs and changes over time leaving room for future needs.
Gluing the floor goes against that BUT the mechanical advantages of a solid floor are hard to overlook.
How difficult would it be to tear, scrape the flooring should it need to come out.
I think if I decide on this method, and think I will be, I would generously paint and seal anything made of wood down there inside and out and use beefy wood support as insurance.
Top layer would need to be easily replaced as that usually wears over time.