If you plan to finish the floor in the attic and turn the room into a living space however you should always use 3 4 inch.
Attic walkway plywood.
Continue the process until the flooring is finished.
Place the first plywood sheet on top of the 2x structure starting by the attic entrance.
Installing attic flooring for light storage only if your attic joists won t bear the weight necessary to finish out a living space but the engineer cleared them to support floor decking for light.
If you plan on placing the plywood around the perimeter of the opening or door and using it only to store light boxes or materials 1 2 inch thick plywood should suffice.
After that screw it in place using the 2 inch deck screws.
We normally recommend that you place plywood over the top of the rafters creating a walkway to the a c and in that area only lay in one or two layers of unfaced fiberglass blanket on top of the plywood walkway and around the ac unit itself.
Apply construction adhesive on one side and place it on the horizontal chord.
No matter what the spacing is on your ceiling joists 3 4 inch plywood should be used if you plan on walking on it.
Ensure that the end of the first plywood sheet lands on a piece of 2x leaving enough room to position the.
The surface itself just has to be strong enough to handle your weight along with tools and gear.
A 4 foot long plywood strip will need at least 8 screws on it.
1 2 plywood or osb should be enough in my non pro opinion.
The plywood should be laying on top of the subfloor with no overhang.
The first plank is placed at the entrance of the attic walkway on the first horizontal chord.
Once the boards are in place place more screws placed 16 inches 40 64 cm apart to hold the plywood to the subfloor frame.
The intent is to lay down the boards and the ends should attach to a ceiling rafter.
Some people extend the wood up on 2x2s across the rafters to clear insulation but care would be needed to prevent that from slipping.
I would not feel right about walking on the fiberglass but for all i know it could be ok.
Once you re done laying down all of the plywood your attic floor is finished.
Plywood is lighter to carry which is good.