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Is 1/2 Inch Rigid Foam Insulation Board Strong Enough Over Open Framing?

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  • Member since
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  • From: 10,430’ (3,179 m)
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Posted by jjdamnit on Tuesday, March 22, 2016 12:30 PM

Hello all,

Half-inch foam is pretty flimsy stuff. I use it for scenery only.

For a base I would use 1- or 2-inch foam over an open grid work.

The 1-inch version comes in 2'x8' pieces with tongue & groove edges. I used this screwed to a base of 5/8-inch medium density fiberboard.

So the screws would not pull through the foam I used finishing washers to give more grip.

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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Posted by BroadwayLion on Sunday, March 20, 2016 11:33 AM

LION did it! Or was it 3/4"...

LION does lots of things because he doesn't know better. After all, what *does* a LION know?

If works, is fine, If works not, fine too, him will change it..

LION made many small table-lets and then could  locate them in the right place and support them in the corners, instead of supporting something every 16 inches or so.

Don't make your supports any closer together than 16". That is what it takes to get a drill inbetween the supports, just incase you need more holes in your wood.

 

 

ROAR

The Route of the Broadway Lion The Largest Subway Layout in North Dakota.

Here there be cats.                                LIONS with CAMERAS

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Posted by skagitrailbird on Saturday, March 19, 2016 8:38 PM

I used 1/2" Gatorboard for a view block. I believe it may be slightly stiffer than 1/2 foam insulation board but I would be reluctant to trust it with three steam locomotives.

What about using millwork strips as stiffeners to either Gatorboard or extruded foam? I suggest gluing something like 1/2" by 2" strips on edge--one single piece diagonally from two opposite corners and two half pieces from the other corners to the center point. Where the strips meet I would attach (glue & screws) a 6+/-" circle of 1/4" plywood or hardboard to eliminate buckling of the two half strips of millwork. I think this would still be fairly light weight and wouild provide something to grip when removing the cover.

Good luck!

Roger Johnson
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Posted by cowman on Friday, March 18, 2016 6:55 PM

I have never used it, but how about Gatorfoam (sp)?  I have seen it at shows, seems quite strong, is lightweight and comes in 1/2" as well as other thicknesses.

I can order it at my local sign shop, some things can be ordered in 1/2 sheets if he uses it for other things.

Just a thought.

Good luck,

Richard

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Posted by tomikawaTT on Friday, March 18, 2016 6:02 PM

Frame your lift-out with (nominal) 2x3 steel stud, and put the last part of the 10 footer (bought at Home Depot) across the center.  Put just enough 1/2 inch ply 'cut cookie' in place to support the track and building, then fill the rest of the space with foam.

Believe it or not, the steel is lighter than equivalent wood.  It also comes without checks, splits and knots and simply disregards humidity.  Finally, all your fastener needs can be handled with the tiny screws normally used for steel stud assembly - no long wood screws into end grain.

Tools required?  Tin snips, vice grips and a power drill with crosspoint bit.  Lacking tin snips, you can do your cutting with a hacksaw.

Chuck (Modeling Central Japan in September, 1964 - on steel stud benchwork)

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Posted by tgindy on Friday, March 18, 2016 5:37 PM

My high school HO layout (6'x6'), and; later N Christmas layout (4'x4').  Each used 2'x4' open grid benchwork on 1"x4".  The base was on 1/2" homasote, not foam, and each layout was plenty strong to lean on -- I wouldn't attempt "any lean" on foam.

Conemaugh Road & Traction circa 1956

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Posted by zstripe on Friday, March 18, 2016 9:14 AM

Rich,

I would use this.....Birch Plywood, cut off two ft. I would rather use Baltic Birch, much stronger and it is 9ply, but Home Depot don't carry Baltic. What they carry, I believe is 7ply, lightweight also...the heck with foam.

http://www.homedepot.com/p/Birch-Plywood-Common-1-2-in-x-2-ft-x-4-ft-Actual-0-476-in-x-23-75-in-x-47-75-in-1503004/202088758

My Son's and I have made quite a few things with the Baltic Birch, from bookshelves to computer desks...all extremely strong.

http://www.woodworkerssource.com/blog/tips-tricks/your-ultimate-guide-to-baltic-birch-plywood-why-its-better-when-to-use-it/

 

 

 

Have Fun! Big Smile

Frank

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Posted by Choops on Friday, March 18, 2016 9:12 AM

or add couple extra layers of half inch slightly smaller to fit in the opening glued to the bottom.  Will be very strong and light.

Steve

Modeling Union Pacific between Cheyenne and Laramie in 1957 (roughly)
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Posted by Tom M. on Friday, March 18, 2016 7:36 AM

Why not start with a 24x24 2" thick piece of foam.  You can cut a lip around the edge that's only 1/2" thick.  That way, you'd have the full rigidity of 2" foam over the expanse of the opening and the flush height of 1/2" you're looking for.

Tom

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Posted by carl425 on Thursday, March 17, 2016 9:38 PM

Build a grid of 1x2's that will fit into the hole, then glue and screw (use some big washers) your 1/2" foam to the top of it.  A 1x2 box with a cross member (or even 2) with the foam on top will be more rigid and lighter than a 2' square of plywood.

And btw, I think over time 1/2" plywood will sag with a 2' span.

I have the right to remain silent.  By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.

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Posted by sdCowboyBen on Thursday, March 17, 2016 7:17 PM

No. I have almost the same layout as you do...1/2" plywood with 2" foamboard and then 1" blue board (St...foam.) It completely holds me up without even a dent in the top piece. The weight of 4 locos is considerable and without the plywood base the locos might/would be disasterous. A suggestion here...take a 2" piece of foamboard the same size as the opening or the piece you are actually going to need in its place and add one loco. Keep adding until you feel it is unsafe. My guess would be 3 locos. If 4 locos make the foamboard sag you have gone too far. But what exactly do you want? Being safe and still using the plywood and foam? If your answer is safety and the possibility of locos falling off the layout you have your answer. Plus a 2 x 2 ft piece of plywood is cheap and light.Cowboy

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Posted by richhotrain on Thursday, March 17, 2016 6:29 PM

gregc

I'm guessing that without any support, it will sag.   I built my layout with 1" foam on top of 1/4" luan.   Can you get 1/4" foam or use a hot wire?

 

Yeah, I could, but I am becoming convinced that I should use 1/2" plywood.

Rich

Alton Junction

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Posted by gregc on Thursday, March 17, 2016 6:21 PM

I'm guessing that without any support, it will sag.   I built my layout with 1" foam on top of 1/4" luan.   Can you get 1/4" foam or use a hot wire?

greg - Philadelphia & Reading / Reading

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Posted by richhotrain on Thursday, March 17, 2016 6:01 PM

Alton Junction

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Posted by beartracks on Thursday, March 17, 2016 5:54 PM

Use 2" thick extruded foam board (pink or blue insolation board)

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Posted by richhotrain on Thursday, March 17, 2016 4:30 PM

UNCLEBUTCH

I dont think I would try it. Too mutch flex in 1/2 in. 24 is a fairly good span.

I would instead; try 1/2 plywood ,liter then part. board.

or add cleats and drop a 2in foam into the opening,to bring top level.

just thinking

 

Yeah, I am thinking that you are right about 1/2" foam board flexing. Maybe 1/2" plywood is the answer, as it is lighter than particle board. I chose particle board originally, thinking that it would lay flatter than plywood. But, particle board sure is heavy.

Rich

Alton Junction

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Posted by UNCLEBUTCH on Thursday, March 17, 2016 4:14 PM

I dont think I would try it. Too mutch flex in 1/2 in. 24 is a fairly good span.

I would instead; try 1/2 plywood ,liter then part. board.

or add cleats and drop a 2in foam into the opening,to bring top level.

just thinking

  • Member since
    September 2004
  • From: Dearborn Station
  • 24,280 posts
Is 1/2 Inch Rigid Foam Insulation Board Strong Enough Over Open Framing?
Posted by richhotrain on Thursday, March 17, 2016 3:56 PM

My layout is 1/2" plywood over 2' x 4' framing, plenty strong to support locos and rolling stock.

In a remote portion of the layout, I have a 24" x 24" pop up hole, also framed by 2' x 4' lumber. Currently, I have a 24" x 24" piece of particle board covering the pop up hole, and a three track back shop sits on top of the particle boaerd, again plenty strong.

But the pop up cover is too heavy for my liking, so I would like to replace it with a 24" x 24" piece of 1/2" thick of rigid foam insulation board. Do you think this would be strong enough to support as many as three steam locomotives?

Rich

 

 

Alton Junction

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