Hi Everyone! Itís been a loooong time sine I have been on here! Iíve purchased a Sunglo Greenhouse and we are about to start the foundation. The instructions from Sunglo show a detail of a gravel foundation using 4x6 rot resistant lumber with the 4x6s and about 5 inches of gravel below grade, and at the bottom of that is 6mil vapor barrier. My question is what purpose does the vapor barrier serve or what is its function. It seems to me that it would prevent water from draining through but perhaps there is something I am not aware of? Any help would be greatly appreciated!TIA!