My deck has gotten really weathered, so I'm looking to replace the boards with Trex or a Trex clone. It looks pretty straightforward, but I see one problem (so far). It appears that part of the original deck was enclosed to make a porch, which means the porch wall covers some of the boards. I can't figure out how to cut the exterior boards flush with the wall so that I can butt the Trex up to it. (See photo). Anyone have any ideas on how to proceed?