Place a 2 inch by 3 inch board directly on top of the joist nearest to the edge of the attic with its largest.
Attic insulation flooring on top.
What you could do is you could put insulation down in the floor joist first then plywood over it and then you could add another layer of unfaced on top of that.
If blown in insulation is used control the height or thickness of the layers so boards can by laid over top without having to compact the filler.
Place flooring over insulation to make your attic space functional.
You do not have to mess around with insulation or extra timber toolstation sell something called loft flooring legs they come in packs of 12 and cost around 17 they fix to the top of the joist and raise the floor by 175mm and anyone can do it they are only suitable for lofts though and are not structural so cannot be used if you intend on using the room as habitable.
If there are recessed light fixtures in the ceiling below the attic be careful not to lay insulation on top of the fixtures.
Even if you re not planning to add any more insulation it s a good idea to confirm that the insulation already in place isn t blocking any vents.
Modern technology of blanket insulation today is considered the best insulation for attic.
Also since the attic insulation rests on top of the drywall it will be much thicker than the bottom 2 4 chord of the attic truss.
Among commonly used types of insulation there are mineral wool or fiberglass rolls and batts rigid fiberglass board loose fill materials cellulose mineral wool etc.
But you know i would rather see you just sort of map out the area in the center of the attic that you re going to use for storage and fill up the rest with insulation because that s the way you re going to get the most energy.
Adding flooring and storage on top of fiberglass insulation will compress it squeezing out trapped air rendering it virtually useless.
Rolls and batts are produced of mineral wool and fiberglass.
Attics are generally covered in batting or blown insulation.
Watch this easy diy guide on how to fit an attic sub floor and boards.