The plywood floor in my shed is falling apart and needs replacement. Should I replace with PT plywood, or PT tongue and groove decking? Which would be better and why?

I guess plywood I just cut, lay down and nail. If you think I should go with decking, what size and any installation tips?

Thanks

 

You need to first determine why your current floor is falling apart. Is it not strong enough for the load? Has moisture made it fail? if so, how close is the bottom side to the ground? is there any ventilation under the floor?

 

After you have torn out the old floor, install a vapor barrier on the ground, then install the new floor. I would suggest P/T plywood. Air needs to circulate under the shed.

 

I think the floor is going for 2 reasons. First I don't think they used thick enough plywood it seems to be only 1 half inch Second the rain water use to go right to the bottom of the shed I have sent the gutters on the shed and directed the rain water away. What should I use for vapor barrier under the shed?

 

Use plastic for a vapor barrier - I'm not sure what mil thickness but it would be the heavier one. 5/8" is usually bare minimum for a floor. Depending on the load it's subjected to you might need plywood that's thicker.

Was the shed originally installed directly over the plywood? do you need to lift the walls to replace the plywood? While PT plywood can withstand more moisture than regular ply/osb - it's still not a good idea to let it get wet on a regular basis. The main thing is to keep the new floor dry except for the occasional rain that might come while the door is open.