Permanent Wood Foundation
https://www.greenbuildingadvisor.com/article/the-bs-beer-show-permanent-wood-foundations-pwfs
Codes
Crushed stone footings: Table R403.4 https://codes.iccsafe.org/content/IRC2018P7/chapter-4-foundations#IRC2018P7_Pt03_Ch04_SecR403.4
Treated Wood Foundations: Figure R.403.1(2) https://codes.iccsafe.org/content/IRC2018P7/chapter-4-foundations#IRC2018P7_Pt03_Ch04_SecR403.1
AND R402.1 https://codes.iccsafe.org/content/IRC2018P7/chapter-4-foundations#IRC2018P7_Pt03_Ch04_SecR402.1