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Ray---if your "clear span" is 10.5 feet, 2-2x12"s with 1/2" plywood would be stretching the limits of the header if used to support a second story of a house. I wouldn"t clear span more than 9.5"(113 inches) with 2-2x12"s and plywood. If headroom is a concern, check out the laminated products available. Another method is to use a 1/2" steel "flitch plate" sandwiched between 2 pieces of dimension lumber. That will hold a bunch of weight. Don"t know much about cost comparison so you will have to check that out. I am sure you know that with the header system, all the weight that it holds above will be transferred to the ends of the header, down onto the shoulder studs (use 2 on each side) and down to the foundation, so make sure you have structural support UNDER the king/shoulder studs if they are sitting on the wood floor--- You say the house was balloon framed. What size floor joist were used on the second floor? If 2 x 10 (I doubt), the builder hopefully used the same size 2x10 as the "ledger board" (skirt, ribbon) and notched it into the long wall studs. Usually this was 1" material though. If that skirt was not joined, but spans the open area where they removed your outside wall, that will take some of the load off of the "new" header you plan to install. BTW---For a garage opening of 16", 3-2x12"s with plywood sandwiched between the 2x12"s is normally used in framing. IF it is not nailed well, that "beam" will develop a sag over time, even with just the weight of the roof on it. If you look at enough houses, you will notice there are a lot of "smiling" garage door openings, with corresponding sagging roof ridges. HTH----Tim Tim
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