15 Information on Pressure Treated Wood As of January 2005, the chemicals used in pressure treated wood have been changed. Previous wood was treated with arsenic; however, due to potential long term health hazards, this has been discontinued. New pressure treated wood is treated with copper. The copper in the ‘new’ wood will be corrosive to aluminum as well as other metals. * If you are using the new pressure treated wood, you will need to place a barrier between the wood and your aluminum frame. Popular barriers include 10 mm thick plastic sheeting, a rubber or foam weather membrane, or a row of weather resistant non treated wood such as cedar or hemlock. * Other weather resistant non-treated woods are popular alternatives to pressure treated wood. These contain no harmful chemicals and can outlast pressure treated wood. Cedar timbers are popular choice for greenhouse foundations. If you want to keep foundation costs low, you could purchase a 1x4 or a 1x6 cedar (or other readily available wood) that will not rot and place it on top of the pressure treated wood. If you have proper drainage, the foundation is not sitting in pooled water, and the greenhouse base is sitting on the very outside edge of the foundation, the greenhouse foundation should have a 15 to 20 year lifespan. What Are ‘Greenhouse Friendly’ Solutions To The New Rules With Pressure Treated Wood?