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| Your hand drawing shows a footing with a wall. That isn't a grade beam. That is like the first drawing, a footing and wall in one.
The way you show will be more costly than jut putting vertical and some horizontal styrofoam under the slab and on the inside of the footing. There is also extra digging. Also rodents might like the styrofoam for lunch and a home. Under the slab, they can't get to it.
I also don't thing you need that much gravel unless you need the fill. We always matched gravel thickness to slab thickness.
I would not necessarily use the 2" styrofoam under the floor throughout. I have heard stories of it causing a slab to fail over time. They make a bubble wrap like material for insulation under slabs now, that is a more preferred method... Unless you aren't going to load the slab too heavily.
As drawn, I don't see much wrong with what you have, no reason why it wouldn't work, I just listed a few concerns above.
The main job of it is to provide a thermal break which you show in your drawings.
I wouldn't do it, but that's me. | |
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Insulating a heated floor.
