Hello again!

[Ed Kapuscinski]

I think it depends on what the layout's life will be like. Will it likely be moved? If so, build heavier.

The dimensional lumber frame with foam on top works fine, but sometimes you have to get a little creative finding ways to attach things under the layout (keep a tube of liquid nails handy and have a good hot glue gun).

If you're going with the foam on dimensional route, make sure to include some cross rib support for stability and additional "mounting area" to affix the foam to the wood. Those ribs are also good for hanging hardware from (the numerous terminal blocks under my layout are all generally screwed to mine).

[davefoxx]

@ScrewySqrl,

I think you're overengineering it, but the only real harm is the cost of materials.  I used 2" foam on top of 1/4" lauan plywood over 1" x 2" joists on 1" x 4" L-girders for my HO trains.  The real reason that I wanted the lauan plywood was to give me a place to secure under-the-table switch machines.  With joists spaced 16" to 18" apart, I don't think the plywood is necessary under the 2" foam.  If you want to use 1/4" foam, you're definitely going to need something like 1/2" plywood under the foam.  If it were me, I would use plywood and avoid OSB.

I do think that the pair of 2"x4"s as legs is serious overkill.  A 2"x2" will do it, and either choice would still require angle braces to really stiffen up the benchwork.

Hope this helps,
DFF

[Mark5]

Very cool - what is the projected grade on this?

[ScrewySqrl]

Very cool - what is the projected grade on this?

I plan to use a 3% grade, possibly setting up at 2.25" in height just to make it come out even with 3 Woodland scenics 3% grade risers, or I might just trim up the riser at 2".  havent fully decided yet.