Finish the Ledgers
It's a good idea to double up the rim joists for added strength.
To make sure the rim joists are even all the way around where the new loft will be, use a level.
The crown of a board is the part where the wood bends. To check to see if your board has a crown, look down the edge. You can take the crown out by yourself by using the piece of lumber as a jack.
For added support around the newly installed ledger boards, screw in lag bolts. Lag bolts are strong, and durable.
For an attractive way of giving the joists that will go across the loft something to sit on, add another 2” x 2” ledger board around the bottom of the loft framing.
When working with a crown board, check to see if the board is level by lining it up to another board. It's important to check the crown, because if not, then your flooring will not be level.
A 2” x 2” ledger board can be simply made by ripping a 2” x 4” down the center.
A 2” x 4” piece of lumber is generally closer to 1-3/4 by 3-3/4.