Our entire basement ceiling was covered with 1/4″ plywood, which was the previous owner’s idea of finishing off the space enough to be able to rent out the space. We had to pull down all the plywood to be able to access the joist cavities for plumbing, electrical, etc. Here is a shot of the old plumbing. Any hopes that we had of reusing any of it were quickly downed. It was old cast iron that was about 3/4 full of rust and sediment. Even the drain lines for the tub and sink were corroded to the point they couldn’t be used.