DoubleDAZ posted:Mike, don't overthink this, every method mentioned so far will work. One of the main ideas behind L-girder was being able to use cross-members of different lengths so you could have an irregular shaped deck with curves instead of straight lines.
Unless you change things, yours is going to be a 30" deep shelf around the room with a peninsula in the center of one side. If you compare the L-girder example on the cover of his Linn's book to the bull nose example in Figure 3-1, you'll see that the only real difference is the placement of the rails. Also note, that both examples appear to show a 4x8 sheet where the legs are 2' apart with a 1' overhang on both sides. If you look at Joe's photos, he appears to have legs that are 4' apart with 2' overhangs to support an 8' deep deck, though it could just be the photos making them look that size. The point is you're only dealing with a 30" deep span which would suggest rails 18" apart with 6" overhangs or a rail against the wall with another rail 24" out with a 6" overhang. The peninsula then gets an extra 1-2 rails with longer cross-members.
One advantage to L-girder is that you aren't screwing into the end grain of the cross-members. Another is that the cross-members don't have to be exact lengths like with bull nose framing.
One disadvantage is that L-girder adds thickness to the bench work. If you use 1x4's, you have the rails at ~4" and then the cross-members at another ~4". If you make the deck 36", you have to stoop below ~30" to get under the layout. I don't know about you, but stooping under 30" gets harder every year. Even 42" still means a ~36" stoop.
And, as Tom Tee's photos show, you can do all but the peninsula without any legs if you want to attach cantilevered brace assemblies to the wall studs.
The way I see it you need a 12' long frame along both side walls, a 19' frame along the bottom wall. From what I can see it might look something like this:
Mike, in your case I think Dave’s suggestions are spot on! I cantilevered a 30” shelf on one wall in my small train room
