Undercover Systems Pacific Northwest has the only patented (Patent number: 6,226,941), engineered, structural under deck ceiling. Our system attaches to the support posts of the deck and to your home. It DOES NOT ATTACH TO THE JOISTS OF THE DECK. Integrated in our Clearspan design, is a clear airspace between the bottom of your deck and the top of our ceiling across the entire system. We maintain a void of between 4 to 7 inches between the bottom of the joists and the top of our system, which allows air to circulate and dry out the entire area. If we were attached to the joists, this would not be possible. We are of the firm belief that attaching metal, plastic, or any other material that catches water and debris to wood, even if the wood is pressure treated, will eventually cause dry rot and premature aging. Special Note: ACQ & MCQ PRESSURE TREATED WOOD AND COMPATABILITY WITH ALUMINUMOver the last few years there has been a proliferation of companies getting into the Underdeck business. It seems that their material of choice is Prepainted Aluminum which is readily available from Gutter Supply Houses and gives those companies a ready source for material. Prior to December 31, 2004 the use of Aluminum in an Underdeck Ceiling was acceptable. However, after that date, the Federal Government mandated that Pressure Treated Lumber no longer be treated with Arsenic as the preservative and instead Copper was to be used as the preservative agent. Those changes were made effective January 1, 2005 and all lumber was replaced at that time. The new specification for Pressure Treated is ACQ which stands for Alkaline Copper Quaternary. This new treatment is much safer for workers and others that may come into contact with Pressure Treated Wood. But there was a downside to the change. Most metals with the exception of Hot Dipped Galvanized, Stainless Steel and Copper will be destroyed when they come into contact with ACQ wood. All fasteners had to be changed as well as any other metal products that are used with ACQ treated wood. I my opinion, it is not a question of whether Aluminum will be undermined by ACQ treated wood, but rather when it will happen.