High Desert: Please note I said should, not shall.
Here is some logic that would seem to apply.
1st) columns (posts) on the exterior are permitted to have only a 6" separation from earth, yet columns (posts) under the floor are required to be separated by not less than 8". Section 317.1.4.
2nd) the code requires that pony walls (wood framing members) at the exterior be separated not less than 8" from the exposed ground, unless they are pressure treated. Section 317.1, #2. It doesn't seem logical that pony walls (structural framing members) under the floor would be permitted to be closer than what is required at exterior walls, since the requirement for columns under floor is more restrictive, than for those placed outside.
3rd) when a pony wall is placed below a floor system, it usually replaces not only the posts, but the beam as well. Wood griders closer than 12" from the earth are required to be pressure treated. An argument could be made I suppose to say that the structural wood wall which is acting as a girder replacement should be no less than 12" to earth, unless it is pressure treated.
Yes I know there are other ways to meet materials resistant to decay, but for the most part around here, pressure treated materials are used so that is what I typically reference. In my experience people are rarely willing to pay for those other materials.
Seems logical to me. As I often say, if one were to try and address every possible scenario that could happpen in the code, it would take a truck to carry the code books around. Somewhere logic need sto be applied.
No I cannot give you a specific chapter and verse that says wood walls framed underfloor to replace column and beam construction must be pressure treated when less than 8" from the earth. However, if it gets to be a problem be sure that sooner or later it will be considered as a code amendment. And the book will continue to get bigger and bigger and bigger.
