I might be starting framing pretty soon and it's bringing up question of my own. It's a shelf layout, kind of like around-the-room except it's not going to be room sized (I'll grow into it ), no more than 18 inches deep so I planned on attaching it right to the wall with good metal shelf L brackets right into the wall studs. First question is the framing itself. I've asked the difference between L girder and open grid so I know what each one is, but then looking back at MR issues looking at the articles for the Waterburry extension for idea's it looked like Dave made a lower frame of L-girder and then attached his plywood to a frame that went on the L-girder frame. Could the frame just be made with perimiter L-girder and the plywood attached right to that? Which type would be the lightest. Not sure if I'm going to put everything right on the plywood or on foam board yet though.
I forgot what the second question was so I will have to get back to everyone.
I did something like that last year. A narrow around the walls layout completely supported by L brackets screwed to studs. I made up sections with 3/8 inch plywood and 1 * 4 pine frames around the edge of the plywood. Then I laid 2" blue foam on top of the plywood. Works, is strong enough for trains, although not strong enough to stand on. I ran a 3/8 inch dado down the inside of the 1*4 framing material to accept the plywood, then glued and nailed the frame to the plywood edge. The plywood stiffens the 1*4 just like an L-girder would. The plywood gives me a solid underside of the layout to attach switch machines, wire looms, power packs, and other stuff too. The width of my layout varies from 2 feet to 6 inches. I finished the frames with a couple of coats of oil based paint, sand between coats, and it looks quite acceptable. I bought an electronic stud finder at Wal Mart ($18) which worked well.
David Starr www.newsnorthwoods.blogspot.com