The height of the rough opening must be 1 5 inches taller than the garage door you intend to buy.
Making garage door opening taller.
If you have the room on the back side of your garage you can make your garage into what is called a jack jill garage.
This means building a wall that spans the entire distance of the opening and is strong enough not to move until you are done.
If you are lucky it s in good shape and either made from 2x12 s or even better a glulam beam.
To put it into perspective if the garage door is let s say 8ft tall make the height of your opening 8ft 1 5 inches tall.
Usually 4 or 8 feet.
That made my door height two inches taller.
Because garage doors are usually sized to snugly fit the dimensions of the garage itself making the door larger usually means making the garage larger.
Before removing the header you will have to support the roof above it.
That is the side where your truck is to go you can build out on the back side.