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.
How to floor an attic plywood.
The previous homeowner may have simply covered the joists with plywood to use the space for storage.
In that case you will need to use 3 4 thick plywood.
Alternatively your attic may already have some sort of floor but this doesn t necessarily mean you can build rooms.
Carry a piece of plywood to one of the far corners of the attic and lay it on top of the installed boards.
Screw the frame to the joists to secure it in place making sure not to screw into electrical wires.
Rip 1 2 thick plywood to 24 widths so it will fit up the attic stairs.
However the same can t be said if you are planning on using the space as a living space.
As an alternative 3 4 osb can be used.
Another option is to skip the plywood flooring altogether and use dimensional lumber.
First you ll need to measure the area you want to floor so you can calculate how much wood you ll require.
The plywood should be perpendicular to the joists so that a signal sheet spans multiple.
The thinner plywood is acceptable when the joist spacing is 16 inches.
1 x 6 3 spruce is a step up from pallet quality wood but makes a fine usable floor in an unfinished attic space.
You ll have to construct a wooden frame or sub floor with boards 16 inches apart to provide extra support for the floor.
To floor an attic you ll need to install a sub floor for support before laying your plywood floor.
Attics with existing flooring.
An attic can be floored with 1 2 cdx plywood if it is being used only for storage.
Don t use 7 16 osb as it is intended for external sheathing and isn t strong enough to be used as a floor.
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 storage you can install inch plywood or.