This topic gets discussed to death and beyond every two months or so. The forum has a search function; I'd suggest using it instead of waiting for a number of posts many of which may be irrelevant to your question.

Truthfully, construction foam, the pink or blue stuff, has no sound deadening qualities, so I'd personally recommend something like Homasote topping the plywood if track noise is at all a concern.

Most overbuild O-Scale because engines and buildings are larger and heavier. 3/4” ply is more stable than thinner materials and many modelers live where humidity can be a problem in basements. Bob Barrett did a series in the OGR magazine showing how 1/2” ply and 1x3 lumber works just fine. Some think foam helps with sound, it doesn’t, but most use it on top of ply to carve rivers/valleys and create mountains, tunnels, etc. Homasote is the sound deadener material of choice, if you can get it, if sound is a concern and if you can afford it. Lots of layouts have been built with ply and cork or foam roadbed, so it’s a pretty personal choice. Some folks use just rigid foam for holiday layouts because it’s light. I used it for a temporary (3 years) 8x10 holiday layout and had no problem with sag, etc., but it was noisy. Obviously, you couldn’t climb up on it, but with 12” 1x3 framing it was plenty strong enough for my purposes.

My layout is mostly on foam. Big issue is that foam wont hold a screw. Unlike HO which is, more or less, too small to screw down, O track is easily screwed down with #4 screws, and most people seem to have an aversion to glue for one reason or another. If you build it like an HO layout and glue the track down, there's no reason why you cant do it on foam. I glued track to the foam with plain old white glue.... works fine and hasnt walked off yet.

My layout is 1/2 " plywood with 1x2 ribs throughout the middle and around the edge.  Then covered with astroturf and mounted on 2x4 framing.   Each section can be unscrewed from the 2x4 frame and reused elsewhere.  Currently I'm in the process of moving the layout 907 miles.  I will reconfigure the astroturf/plywood sections and the 2x4 frame to suit the new location.

I frequently walk or stand on my layout to reach overhead storage.

I used 3/4 plywood + foam on my old Standard Gauge layout.  I feel that 3/4 is overkill, and I'm planning on using 1/2 for my soon-to-be-started O gauge layout.  I am also NOT going to use foam.  Like others have said, it won't hold a screw and it did not do much for sound. 

I also never plan on walking on my layout.

IF YOUR FAME IS SOLID', 1/2 INCH LUANN PLYWOOD WILL WORK JUST FINE'. cork or foam road bed will help with noise. Luann is very inexpensive plywood. The table is key as far strength and weight considerations are concerned'.. Good luck'..

@Boilermaker1 posted:

My layout is mostly on foam. Big issue is that foam wont hold a screw.

I followed Ken's suggestion in his excellent book

21 Great Track Plans for Compact Layouts by Ken Hoganson

He suggested poking a hole in the foam with a screwdriver, dropping gorilla glue into it (which expands when it dries), screwing in a 40lb metal E-Z anchor, allowing it to dry, then using #6 screws to fasten the track to it.

John

I user 3/4" plywood then put 1/2 homosote ontop of that.  I have been happy but I need to be able to get ontop of the layout to reach some places.  It is certainly overkill but I am glad I went homosote vs foam.

My O SCALE train has three tracks, so a little noise is not a problem. I bought my MDF sheets for $2.00 each from a trucking company that wrecked a load. The sheets were 120" x 61" x 1". I bought enough to finish the interior of my 42x36x12 pole building with plenty left to do my 45'x16' on the end layout, it is a duck under that sticks out the 61" inches from the wall. So back to the question, I do not worry about noise, or rivets or anything else. This is a hobby, something to relieve stress not create it.

One thing that'd be nice with a foam base is the ability to easily carve out ditches and bodies of water. Coming from someone with a plywood top. I do like the plywood overall thought.

I have 1/2" ply with 1 1/2" foam, topped by ceiling tile on my all Fastrack layout. Noise is not a problem, as engine sounds at 50% are easily heard over any track noise. I used L-girder construction, and have had my 220# on top many times.

I used 5/8" plywood with cork for the roadbed. For the cork, I used tiny finish nails to position. This allowed for minor adjustments without destroying the cork during development. The track is Gargraves, so #2 flathead wood screws were used to secure and allow for track adjustment. The use of ballast and scenic cement secures but also helps deaden the sound.

The book by Lynn Wescott served as inspiration for benchwork, just be sure to design your benchwork (and wiring) to be modular. This obviously helps with any future move but also allows for salvaging sections should the new space not be configured the same.

For my expansion I went with foam over L girder framing.  As far as attaching track i poked finish mails through pre drilled holes to fix the alignment.   Once the track is ballasted it won't be going anywhere.  As folks have said noise is an issue.  I started with left over cork roadbed but that proved to be worthless.  The foam roadbed from i think is from scenic express proved to be superior and affordable. 

Looking at the HO'ers layouts; I used pink foam that was cut with a band saw to form terrain. but soon discovered that the foam, as has been said, won't hold a screw. So, I used polyurethane hot glue to hold down the track.

At that point no changes can be made. Plus, the foam support was way too weak and to keep it I needed to lose a lot of weight. Which would not have been a bad thing for me to do.

INSTEAD, I removed all of the foam and replaced it with 1/8" Masonite on 1x3s.

I have a 1/8" neoprene rubber layer on my plywood topped layout.  with ross/gargraves track it is very pleasant to listen to, takes away the plywood din nicely.

A question for people who use a foam top. What kind of foam do you use? I don't want the weight of the trains to break down the foam, and I like the ability to carve.

Pink insulating foam 2" thick over 3/8 or 1/2 plywood.  3/4 ply is overkill.  Track can be adhered using Loctite PowerGrab adhesive - water cleanup.

@Boilermaker1 posted:

My layout is mostly on foam. Big issue is that foam wont hold a screw. Unlike HO which is, more or less, too small to screw down, O track is easily screwed down with #4 screws, and most people seem to have an aversion to glue for one reason or another. If you build it like an HO layout and glue the track down, there's no reason why you cant do it on foam. I glued track to the foam with plain old white glue.... works fine and hasnt walked off yet.

I used #6 Plastic Wall Anchors glued with Gorilla Glue to hold the Anchors in place under the Fastrack. Used #6 drywall multipurpose flat head screws to hols the Fastrack down. Just lay out your track on the foam and push down a small drill bit through the track holes, take an anchor with a screw attached, push down about 3/4 of the way into the foam, pull it out, squeeze a dab of glue around the inside of the hole, put in an plastic anchor, tap it in with a hammer to make it flat and let the glue dry, do all your holes the same way. Screw in screws by hand with a screwdriver, a power drill will rip them loose.

I used 4 layers of 1” pink rigid foam over 3/8” plywood.  It’s plenty sturdy, and you can easily carve water features and valleys.   I use LOTS of Liquid Nails to put things together.  Just a dot of Liquid Nails here and there under the track will hold it, especially after ballasting.  

I was thinking about using the foam formed roadbed with Atlas track. Of course, if you're going to glue the foam roadbed to the base foam you will want everything well sorted out ahead of time. Anyone with experience using this foam roadbed think this would work? The formed roadbed would hold the track in place and terrain could be carved out of the base foam. Ballast could then go on top of it for the track.

This is a timely topic as I'm building my benchwork. I went with 1.5" EPS with a silver back for Legacy signal strength. That foam is going to be on top of a piece of plywood but I haven't decided how to attach the two. I was hoping the foam would deaden the sound some but it sounds like I'll be relying on my roadbed for that. I mostly wanted to avoid having a flat surface for my railroad. I think being able to melt/carve the foam will give me tons of scenic opportunity via small dips and whatnot. That's what I'm excited for.

On my present layout I used 1/2 inch OSB  underlayment with 3/4 inch high density foam purchased from Menards.  Foam is attached to the OSB  using latex caulk. I only get dents/divots in the foam board if I put too much of my own physical weight on the board.  Track is attached the same way, black or clear caulk,  held in place with 2" wafer head screws until the caulk cures, then removed.  Then the tracks are ballasted to ensure rigidity.

I mostly wanted to avoid having a flat surface for my railroad. I think being able to melt/carve the foam will give me tons of scenic opportunity via small dips and whatnot. That's what I'm excited for."I would love to do that; however, I have issues with changing traction tires, so I have opted for this layout to keep the track bed level.