Problem is the attic has 2x4 engineered trusses spaced every 2 feet apart,
so I would have to add joists to support the weight of the floor, the weight
of anyone walking up there, as well as the weight of the boxes and things
that I'll be storing up there. I'm planning on using 3/4 or 1 inch plywood
for the flooring in the garage attic.

The garage is 22 feet wide (the trusses go this way, so the trusses span 22
feet) and 20 feet deep. Would I need some kind of beam going down the middle
to support the additional joists, so they wouldn't have to span the full 22
feet?

What's the easiest way to add and support joists and a floor in a 2-car
garage attic? The 2x4 trusses are, of course, resting on the walls of the


You don't want to mess with or add weight to the trusses, unless you
can do the math to figure out what they're going to do in response.
You can add a floor anyway, but figuring out how requires knowing
things like: How much headroom is there in the garage for
beams and joists sticking down? Which way do the existing trusses
go relative to where the garage door(s) are, and to the roof-slope?

Remember that you don't actually have to have a load-supporting floor
over the entire area, either. If you can find a place to plant
3 or more posts supporting 2 or more beams either under, over,
or between the trusses, then you can put a platform in.

It might even be cheaper or simpler *NOT* to put a regular floor
in, but just put up scaffolding through the trusses with planks
across them.

--Goedjn