I have two questions:

1) I am installing tongue and groove ply, 3/4 thick. The long edges have the t/g, while the ends do not. Do I need to maintain a gap between these end joints?

2) Should the felt paper be unrolled parallel or perpendiculay to the direction that I will be laying the hardwood? Not sure if the overlap cause any flatness issues.

Thanks,
Steve

My understanding is to leave an 1/8" spacing sides and ends regardless of whether it is a subfloor or an underlayment over a subfloor. The tongues should be slightly longer to the sides automatic for you.

I prefer felt to run perpendicular whenever I can get by with it. Most times I can't because the rooms not completely empty. I butt the joints and mask tape the seams. Flipping the felt over will help it lay flatter.

Thanks Jerry!