I am planning to use 2" foam over 1/4" plywood as my base. To support this I plan to use 1x4 frames. What spacing is needed between boards? It seems the standing building practice of 16"OC might be overkill. What suggestions do you have for this?
Actually, 16” IC sounds about right over 1/4” plywood.
Rich
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Welcome to the forum, DrJohnhurst!
On my layout, I used 1X4 every 16". I also thought it might be overkill, but making them further apart would have saved only two boards for my layout size. I decided to go ahead.
A word of warning: If you’ve read this forum very long, you’ll find everyone has their own opinion on how to build benchwork, and if you do it differently, you will hear about it.
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LOL, so true.
Rich
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Welcome to the form Dr johnhurst
How is the foam attached to the plywood? If it’s glued on over the entire surface, you may be able to go farther than 16".
But as @York1 said, it may not be really saving you much lumber.
I used 1" x 4"s with 2" foam but no plywood. I found working through foam and ply a pain in the past, I would go with one or the other.
My spacing is 24" x 16" on the grid work, all 1" x 4"s put together using lap joints.
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It wasn’t with foam but what I always did with my 1x4 framework was one in the middle and if it was very long (>4’) I’d put one more in the center of the two remaining sections. Better to overengineer than underengineer.
Now I am second guessing my plan to use plywood under the foam. Is 2" foam board strong enough to span 16" spacing without flexing the scenery above it? How would things like Tortoise machines be mounted to the bottom of the layout?
Mine has been there for 20 years and is still solid. For Totoise switch machines, just glue a square of 1/4" ply underneath where you want to attach the machine.
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The plywood top would add a lot of strength to the framework. Foam adds no strength.
1/4" plywood is not very stiff, I’ve seen 1/4" plywood sag under it’s own weight with 16" spacing. If I were to use plywood, I would either step up to at least 3/8", glue the foam to the plywood for added stiffness, or drop down to 12" spacing. However, the two inch foam will be fine on 16" spacing, that is assuming you’re talking about the 25 psi insulation panels.
FYI - for an easy and clean way to cut holes through the foam, get some thin wall brass tubing and chuck it in a drill, it will cut through the foam like a hot knife through, well, foam.
My layout is 2” foam glued on top of 1/4” lauan plywood with construction adhesive (Loctite Power Grab). I did this for two reasons: (1) to provide support to the foam, and (2) even more importantly, to be able to secure under-the-table switch machines. The 1/4” plywood is sufficient to install switch machines with small pan-head screws. The construction adhesive prevents any sag of the 1/4” plywood.
I just checked and found that I went with approximately 18” spacing on the joists (in my case 1”x 2”s). I went lightweight for portability, and there has been zero problems in the eight years since I started construction. The 2” foam is fairly rigid, so it and the plywood are more than sufficient to hold up your track, trains, scenery, and structures. Unless you’re planning to walk on it, this is plenty sturdy.
DFF
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I think 1/4" ply adds nothing to the structural integrity and just creates more work, cost and as I said earlier, working through both foam and ply is a real pain IMO.
All 180lbs of me have climbed up on my foam, kneeling on a 20" x 30’ piece of ply and there was no evidence I was ever there once I got off. We are not holding up refrigerators and waterbeds on our layouts, we are supporting a few pounds of toy trains. Build to prevent flex and don’t worry about the weight.
In this photo you see a 1/2" piece of ply on the end nearest the camera, I have it there as I have a lot going on in that spot and it made making the round end much easier. I put 1-1/2" foam on top so it lined up with the 2" on the rest of the bench.
The bench in the foreground in 6’ x 18’ and two people can carry it without much effort, yet it is solid and doesn’t move.
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