Pressure-Treated Foundation?

I am building an 8x20 insulated porch/addition to my home in the northeast USA. The house has a full basement but I planned on putting the addition on concrete piers and either insulating the floor or putting an insulated skirt around the perimeter. Then I talked to a neighbor who has been building up here for decades and says just sit the whole thing on a 20 foot PT 8x10 or 10x12 on the ground (which is all sand around my house). Lay some 2' pieces of PT 2x10 under it every 6' in case it ever moves or shifts you can easily put a shingle under there. He says concrete doesn't work well up here because it cracks and shifts, but the buildings he has built just sitting on large PT timbers generally stay level. There are lots of big old barns around here that are just sitting on big timbers resting on flat stones.
Is it OK to do it this way? I am in a part of Vermont where there you can build things pretty much how you want. Thanks,
-- Jeff
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The old PT wood lasted forever but contained arsenic which was outlawed as a component. The new stuff may not last as well.

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Art wrote:

The old stuff was not outlawed,...the manufacturers voluntarily replaced it due to the continuing threat of lawsuits from misguided people that are terrified of the word arsenic.
Just wanted to clarify that.

--
Robert Allison
Rimshot, Inc.
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