Humidity prevention under cabin, sand and plastic sheet?

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Small Cabin Forum / Cabin Construction / Humidity prevention under cabin, sand and plastic sheet?


Author	Message
robmorin Member	# Posted: 25 Jun 2014 11:37am - Edited by: robmorin Reply Hello, I am building a small 12' x20' cabin in Quebec, about 2 hours north of Montreal, my local lumber yard where I purchase the wood from, said to prevent humidity under the cabin as to help prevent any kind of rot(although I am using PT lumber) is to put a layer of sand, like 2 inches, then a sheet of plastic over the sand and then another 2 inches of sand, he said it acts like a giant sponge?? My cabin is on cinder blocks about 8 inches off the ground... Anyone heard of this technique? Thanks Have a great day!

bldginsp Member	# Posted: 25 Jun 2014 12:39pm Reply Never heard of it. Vapor barriers (plastic) are used under concrete slabs on top of gravel to provide a capillary break that inhibits water in the earth from working its way upward. But if you have a clear 8 inch air space under your cabin that's best. But critters might want to live there so you might want to close it off, if so, use vent screens to allow cross ventilation under the floor for moisture to dissipate. If the earth under your cabin stays wet due to high water level then you might need to take some sort of action such as described, but I've never heard of it, but I live in sunny dry California. If you do have a wet condition, don't assume the PT lumber is all you need to deal with it. PT just forestalls the inevitable in a wet situation.