I have a 5x9 frame and I just attached a 4x8 piece of plywood (1/2" thick). For the rest, I am going to cut down another 4x8 into a 1x5 piece and a 1x8 piece. I am attaching with drywall screws per the manufacturer's suggestion. My question is when I am lining the plywood up, should I leave a 1/8" space for the wood to expand like construction sites recommend, or can I line it up flush? For what it's worth, I am building in a basement that runs between 25 and 50%(ish) humidity. I will be covering the wood with 2" insulation foam, which obviously will be flush.