huangyhg

wood touching insulated concrete - pressure treated or not?
i have a concrete wall in a heating only climate that is insulated from the outside, insulated from the ground, and sits on a percolation barrier. the question is does the wood that contacts the concrete need to be treated?
reasons (i can think of) wood touching concrete should be treated:
1. moisture percolates up through concrete wetting wood (can't in this case)
2. cold uninsulated concrete can cause condensation of moisture that touches wood (can't in this case)
3. fresh concrete is still evaporating bleed moisture (how long does this happen?)
only the 3rd case is a possible reason to use treated lumber in the spec'd case, but i don't think it could be a log term cause of rot. any thoughts?

i'd check to see what local conditions are. as a minimum, i'd bear the wood on 'tar' paper (asphalt impregnated building paper).
dik
i believe the building code requires these to be treated timber.
concrete retains a significant amount of interstitial moisture for many years. that moisture routinely moves in and out of a vapor phase, depending on the temperature and relative humidity. placing anything that is reasonably "barrier like" to moisture (which wood is for the short term) can cause that moisture to collect under that material in a liquid phase. this is one reason the wood needs to be pressure treated.
another reason, is that concrete is aggressively alkaline. in the absence of pressure treating (usually acidic), the wood will dry out and its cell structure will be damaged from the exposure to the drying/alkaline condition. this is another reason it should be pressure treated.
the code requires it. this is another reason it should be pressure treated.
use pressure treated wood.
check with your local code officials
i agree that treated lumber should be used - there are several common choices of lumber treatment, some more suitable than others. if your application will have the wood in an occupied space, suggest that you consider borate treated lumber or acq (alkaline copper quaternary). use of acza (ammoniacal copper zinc arsenate) or the formerly common cca (chromated copper arsenate) are not advised because of the arsenic compounds present.
any wood touching concrete needs to be treated = rot and mildew? yes, but none of the above have listed a more frequent "invader." without protection inside the wood, termites will get in and rapidly spread, regardless of whether the concrete is "dry" or still curing.
it's worse now with today's enviro restrictions on good (long-lasting) insecticides.
if you select wood treated with borate or acq, make sure you properly specify the coating for any metal fasteners in contact with the wood. these new wood treatments corrode metal much faster than the old treatments.

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