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Old 07-31-2021, 01:04 PM   #1
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Subfloor question

We are seeing a million ways to skin the cat on subfloor and flooring insulation.

From -

Metal floor + rigid foam + t and g

Metal floor + 2x support boards with foam between + t and g

To a million other options.

So what did you do and why? We are getting close to this part of the build and don't quite have a decision in what to do.

Thanks in advance!

Dan
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Old 07-31-2021, 01:20 PM   #2
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Way 1,000,001:

I welded wood screws to the steel floor (point up), then laid down 2" XPS foam board, then spun 2" long pieces of oak dowel rod through holes in the foam onto each welded screw. Then I put down 3/4" plywood and screwed it to the dowels. The insulation is as good as a "floating" floor but it has a solid mechanical connection between the plywood and the steel floor (not just relying on glue like a floating floor) without putting any additional holes in the steel layer.

The downsides are that it's more work than any other method and it's a bit hazardous to be walking around with all these caltrops on the floor (it's also a bit more expensive, since oak dowel ain't cheap). Very pleased with it - now that's it all done.
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Old 07-31-2021, 03:53 PM   #3
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1/2" rigid foam insulation followed by a layer of 1" glued down,with channels routed for Pex water lines to heat the floor. This is topped with snap together flooring with vapor barrier.
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Old 08-09-2021, 05:22 PM   #4
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Not yet built but we're going with Brian and Erin's (BEAP) way.


Fomular 150 (15 psi compressive strength - Fomular 250 has 25 psi compressive strength if you want overkill) glued to the corrosion treated steel floor.
1/2" plywood sub floor glued to the Fomular.
Finish flooring over the plywood sub floor.
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Old 08-09-2021, 05:32 PM   #5
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Holy cow! That is super detailed!
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Old 08-09-2021, 05:37 PM   #6
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Originally Posted by HamSkoolie View Post
Not yet built but we're going with Brian and Erin's (BEAP) way.


Fomular 150 (15 psi compressive strength - Fomular 250 has 25 psi compressive strength if you want overkill) glued to the corrosion treated steel floor.
1/2" plywood sub floor glued to the Fomular.
Finish flooring over the plywood sub floor.
I don't know why anyone is concerned about the PSI of Foamular, or plywood. That 15PSI is 2000lb per square foot, 250 3600psi. Add 1/2" plywood at 43,000lbs per square foot. We're at 45K persquare feet before adding finish flooring. What are we carrying that we would be concerned about the PSI of the floor?
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Old 08-09-2021, 05:59 PM   #7
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I don't know why anyone is concerned about the PSI of Foamular, or plywood. That 15PSI is 2000lb per square foot, 250 3600psi. Add 1/2" plywood at 43,000lbs per square foot. We're at 45K persquare feet before adding finish flooring. What are we carrying that we would be concerned about the PSI of the floor?

It merely demonstrates that there is no structural need to support the sub floor with framing. The Foam with 1/2 ply over it is more than structural enough to support any load placed on it including the feet of furniture or chairs.

I've just seen a lot of builds where they "support" the subfloor with wood framing and fit fomular between the frames.
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Old 08-09-2021, 06:06 PM   #8
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It merely demonstrates that there is no structural need to support the sub floor with framing. The Foam with 1/2 ply over it is more than structural enough to support any load placed on it including the feet of furniture or chairs.

I've just seen a lot of builds where they "support" the subfloor with wood framing and fit fomular between the frames.
Ya, I could never understand the need for framing the floor for insulation.
I have 1.5" foamular with a vapor barrier for the floating laminate flooring on top.
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Old 08-09-2021, 07:38 PM   #9
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Ya, I could never understand the need for framing the floor for insulation.
I have 1.5" foamular with a vapor barrier for the floating laminate flooring on top.

So you put the laminate directly on the Fomular (and vapor barrier) with no ply wood sub floor between them?
Hows that working out long term? I could save 1/2" of head space and the cost of 1/2" ply these days is insane.
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Old 08-09-2021, 07:45 PM   #10
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So you put the laminate directly on the Fomular (and vapor barrier) with no ply wood sub floor between them?
Hows that working out long term? I could save 1/2" of head space and the cost of 1/2" ply these days is insane.
Everything I'm building is being attached to the walls, so little floor weight. Between 1.5 foamular and laminate at 300psi, what's to worry about.? My floor has a cushiony feel to it which I find comfortable and not like a hardwood floor. The only use the floor will see is walking on, which at my weight is 2.65PSI. I think I'm good.
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Old 08-10-2021, 03:50 PM   #11
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The only use the floor will see is walking on, which at my weight is 2.65PSI. I think I'm good.

That sounds like a static weight distribution. You'd be surprised how many pounds the human body exerts on a surface (and itself) while moving though you're not going to exceed your floors capacity. While running the human body exerts TONS of force upon the surface....as well as the lower legs ..... I know the hard way from research during the Marines trying to alleviate my constant stress fractures from forced runs on asphalt and concrete.
I am curious what type of laminate flooring you're using and how thick it is. We're still at a point where we can adjust floor and ceiling thickness to accomodate my height.
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Old 08-15-2021, 12:50 AM   #12
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2003, we laid one-inch pink-board hard-foam insulation -- designed for wet areas such as a bathroom -- directly on the bare box floor.
On top, we laid half-inch plywood, thoroughly sealed by painting all surfaces.
.
Our visible floor is bamboo plank perimeter with slate in the center.
.
With nearly two decades full-time live-aboard, with two and frequently three adults plus three RedHeelers, traipsing across deserts and rough logger tracks, the pink-board shows no indication of deterioration or compression.
.
Would I do it again?
Yes.
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Old 08-15-2021, 09:00 AM   #13
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We:

1) Treated rust with LDC rust converter.
2) Painted with Rustoleum enamel
3) Tore down a sheet of 3/4” ply into 2” strips and ran them the perimeter of the bus floor and roughly every 16” so they run from front to back. All were glued and screwed.
4) Put 3/4” rigid foam board in the gaps with glue.
5) 3/4” 4’x8’ ply went on top, with the long edge running from window to window (had to trim a little off the 8’ side so they’d fit). Screwed in.

We have a flat nose with the engine up front, and some of the spots around the engine compartment couldn’t be framed with furring strips, so that is just glued board and ply. The floor is definitely squishier there, so I’m glad we put down the strips for both support and a little extra security.

https://imgur.com/a/9eNpDiM
https://imgur.com/a/EClHAky
https://imgur.com/a/BVSZyv0
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