I bought a home several years ago that was manufactured in the early 1990's. It's in one of those neighborhoods that goes up fast, and I'm sure the contract spared every possible expense (no extra anything). At any rate, the attic space of the two-car garage when we moved in had several pieces of attack decking down, and I've added decking to 1/4 of the beams.
The reason I didn't go any further with the decking is there are a multitude of electrical wires that run on top of the beams. The beams are 2X4's that are part of pre-fabricated trusses, 24" on center. I was going to drill small holes in the beams (like you would do in studs) so I could run the wires between them and not over them, allowing me to add some more floor decking. However I did some quick online research and learned in an electrical forum that you NEVER, under any circumstances, drill holes in a prefabricated truss.
Now, I could run the wires on top of the decking I guess, but if a small hole in a beam is going to cause a that big a problem, how well can these trusses support the decking and storage items I'm placing up there? There are definitely NO engineering specs available. Is the decking OK, and what kind of load can this realistically support. Everyone stores a ton of crap in there attic space, right?