Crawl Space Moisture

[TheWire]

I'm building a 20'x32' 1.5 story cabin in Wisconsin.  I have 24" crawl space walls made of pressure treated studs and plywood.  These rest on continuous compacted gravel footings.  I also plan on using pressure treated floor joists.  I have some questions regarding moisture control.  I plan on laying down a vapor barrier on the ground and putting in crawl space vents.  However, I still read about people having crawl space moisture problems because the outside air can be more humid then condense when it gets into the cooler crawl space.  The cabin is on high ground so I don't expect much ground moisture.

Does anyone have experience, good or bad with crawl space moisture on a cabin.

I was thinking of putting on a pressure treated subfloor.  After dry-in I would laydown a moisture barrier on top of the subfloor, then high density foam insulation and osb on top of that.  A double bottom plate would give room for the additional thickness. The PT plywood, foam, OSB sandwich would do 4 things:  Give me more time to build as the floor deck would be pressure treated, give some floor insulation, allow the finished flooring to go on clean OSB,  and all wood exposed to crawl moisture pressure treated so I shouldn't have to worry about moisture.  Any thoughts on this approach?

Thank you,

Jerry

[glenn-k]

I don't like pressure treated with any kind of chemicals in living space --Learned from Oehler for the underground cabin.  People started showing preservatives in blood test's  notably Penta - just living near it.

Everything's always good for about 20 years then when people start growing grotesque new features industry and state comes out and says -- Oh -- well --- I guess that really wasn't so good for you after all.  -- If they even say that.

[Ernest_T._Bass]

Not to mention the expense... You could probably build your whole deck platform from rough-cut cedar for less than PT.

[skiwest]

Building something similair.  I don't think its necessary to make subfloor or joists out of PT.  With 24" you have lots of space between ground and wood.  Only thing I will use PT is skirt that will be in contact with ground.

I put down vb on ground, I had geotextile for road so put a layer of that down , then VB then another layer of geotextile , then sandy gravel form site.

[jraabe]

I agree with skiwest. Your foundation should be PT - as you have mentioned. The joists and subfloor will not need this. You are well above the soil and if you have good drainage of site water and you have a poly moisture barrier over the CS soil then you are in good shape.

Any moisture you see will likely be very temporary and this is no problem as wood will naturally absorb and release short term moisture. I would suggest putting in closable foundation vents and then see when you need the extra ventilation and when you don't. Keep a simple temp and humidity thermometer in the CS and see if it ever gets close to 90%. Ideal readings would be between 40% to 60%.