You can go with a wooden brace but depending on the load on your garage door header the sag could reoccur overtime.
How to replace garage door header.
Sagging garage door header lift system.
The lintellift system is a patented product that ensures garage door lintels or headers won t sag.
Tbe row of 6 blocks have a 2 x 10 on top and a 2 x 10 below them.
The lintellift system fixes this issue by adding support underneath.
And you do that right inside the garage door.
We have an old cinder block garage shed building built in 1967 with 2 9 foot wide garage door openings.
When a garage door lintel fails it causes the brick wall being supported to sag leaving a noticeable crack right above the garage door.
Take some 2x4 s and use these to add 3 rows of supporting frames around the sides of the door and just below the header.
To install the extra header jack your door up to correct the sag and bolt in the beam.
By using a steel beam there is less chance of a re occurrence in the sag.
You basically build kind of a fake wall right up to the underside of those rafters to support them between the garage floor and the underside of the rafters while you do the disassembly and replacement of the header.
Push the new header into place.
Cut three pieces of 1 inch by 11 inch lumber to the width measurement of the garage door rough opening plus 12 inches.
This header should be an inch and a half higher than the garage door and 9 inches wider than the door.
These 9 foot openings are only supported by a makeshift header consisting of 6 cinder blocks sitting horizontally across the top of the opening.