Pressure treated "PT" lumber is made for damp areas, where there's moisture and direct contact to concrete or earth. Make sure to use the proper coated anchors for Pressure treated lumber. such as hot-dipped galvanized or stainless steel fasteners. there's more detail about this below.. keep in mind pressure treated is not only a preservative it is also a poison to prevent termites..
An alternative you can consider using fir or pine as your bottom plates, if on concrete you can't have direct contact. lumber will take the moisture from concrete and either cause dry rot. To prevent that from happening lay down sill gasket a foam like material in a roll.. made for this reason.. and can be found in most home hardware locations..
Commencing in early 2004, the pressure treated wood industry ceased producing CCA treated wood for many residential uses.
A number of replacements have been developed including Copper Azole (CA), Alkaline Copper Quaternary (ACQ) and Sodium Borate (SBX).
With the change, ACQ and CA will almost certainly be the preservatives used in generically designated “pressure treated” sawn lumber
in use in building construction. SBX treated lumber is available but would need to be specified as such.
Practices and customs that were adequate with CCA treated lumber may not be appropriate for use with the new products.
Some of these “next generation” wood preservatives are significantly more corrosive to metal than was CCA treated wood.
Current information suggests that this increase in corrosion particularly applies to CA (and ACQ but not to SBX)
The use of hot-dipped galvanized or stainless steel fasteners with the pressure treated wood, and avoidance of
contact of aluminum with pressure treated wood have been long standing recommendations; although, in practice,these
have frequently been overlooked with no serious consequences (other than pitted aluminum flashings).
With the new preservatives these recommendations should no longer be ignored. Thus it is important to specify and
obtain appropriate corrosion resistant materials to ensure adequate service life for fasteners and connectors.
Aluminum should not be used in contact with pressure treated wood. Spacer materials or other physical barriers are
recommended to prevent direct contact of pressure treated wood with aluminum products.
I realize this is an old post but i hope this information helps people looking for the right answers. if you would like help with anything else look up my page up on facebook- RCM Construction
Given multiple issues there, I think the correct and possibly simplest, albeit messy, solutiion is going to be cutting the floor open and putting the pipes where you need them.
Concrete is not forever.
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Yeah, major mistake from the previous remodel with the the plastic over the insulation. All that does is hold moisture in and create mold. Your XPS and treated lumber sounds like a good plan. The plaster idea is also probably a good final finish idea.
Once you get the framing removed you should see the rough surface of the footing. It may look like pebbles but that should be the unfinished top of the concrete footing. Your wall is not load bearing just cosmetic so if it sits on the rough footing or the basement floor it should be fine.
The perimeter drain tile you spoke of is supposed to be on the outside of the wall at the footing and carry the water away from the house or into a sump to be pumped away.
Good luck!