Step 2 measure the length of a ceiling joist from the midpoint of the garage to the wall of the garage.
Reinforcing attic rafters.
Move the jack in increments of one inch to allow for the roof to be able to move with it without cracking.
Reinforcing the connections between the rafters and the walls will help prevent your roof from collapsing.
Step 1 measure the thickness width and length of the rafters in your home and purchase one piece of framing lumber of the same size for every two rafters in your attic.
The easiest way to straighten rafters is to jack them into position.
However the trick to this process is to do it very slowly so it may take a few weeks before you get the rafter into a position where it is straight again.
Take 2 6x4 as long as your longest stored lumber and cut 2 inch deep grooves in them as wide as your 2x6 is thick every foot or so.
Install these over your existing horizontal 2x6s 2 feet from the roof edge inside and paralel to the roof ends crosswise from your existing 2x6.
Snap a chalk line against the rafters on both sides of the attic to mark the location of the braces.
Keep the spacing 4 feet apart at most.
Place a ladder or stepladder against the rafters to allow yourself to climb up to them.
When using fiberglass insulation the pink stuff the attic roof rafter will need to be at least 16 deep.
Standard joist spacing for the installation of attic flooring materials is 16 inches on center oc meaning the distance from the center of one joist to the center of the next joist is 16 inches.