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Old 04-23-2018, 09:30 PM   #1
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How far apart should sub floor wood strips be (with insulation in between)?

I’m coming up on installing my new floor. I plan on having 3/4” insulation, framed with 3/4” wood in a grid pattern, and covered with 3/4” plywood with a thin laminate on top of that.

But how far apart should wood for the grid be? I’ve seen 16” thrown around for wobble factors, but I also think less wood and more insulation would be better for heating and cooling.

Thoughts?
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Old 04-23-2018, 09:32 PM   #2
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Mine went down with no framing at all. 1 1/2" of XPS foam board with 5/8" ply on top.
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Old 04-23-2018, 09:39 PM   #3
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Mine went down with no framing at all. 1 1/2" of XPS foam board with 5/8" ply on top.
Have you noticed any structural, aesthetic, or design issues that bother you?
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Old 04-23-2018, 09:41 PM   #4
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Have you noticed any structural, aesthetic, or design issues that bother you?
No issues at all. I can't actually think why there should be. Floor is stable and firm.
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Old 04-23-2018, 09:57 PM   #5
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Yeah I was looking at your build wondering if that style would cause an issue with my almost 300lbs on it every day
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Old 04-23-2018, 09:59 PM   #6
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Yeah I was looking at your build wondering if that style would cause an issue with my almost 300lbs on it every day
I feel you there, I’m 260 pounds myself.
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Old 04-23-2018, 10:02 PM   #7
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Yeah I was looking at your build wondering if that style would cause an issue with my almost 300lbs on it every day
The compressive strength of the insulation is 25 lb per square inch.

That doesn't sound enormous but there are things going for you.

To start with, I weigh 180 lbs. Walking around on it in flat shoes, otherwise unprotected, did not put dents in the surface.

Then you cover it with 5/8" plywood which spreads the load over a much more substantial area.

Your 300 lb ain't gonna hurt it.

It's probably safe to assume that with all of your weight on one foot, the area carrying the load is at least 144 in sq ... Which means about 2 lb per square inch.
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Old 04-23-2018, 10:21 PM   #8
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Excellent info thanks man
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Old 04-23-2018, 10:30 PM   #9
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I just looked up your build Twigg and found the pics of your floor, that looks real good. And with your post above, I think I will do the same. Thanks!
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Old 04-23-2018, 10:37 PM   #10
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I just looked up your build Twigg and found the pics of your floor, that looks real good. And with your post above, I think I will do the same. Thanks!
I'm pretty happy with that floor. It should work well even in winter.

I have the advantage of the OEM plywood underneath it, and I screwed through into that layer. I need to add a few more screws but that won't take long. I don't so much want to screw it down, just stop the plywood bowing or moving.

If I didn't have that lower plywood layer I would have sparingly used TEK screws straight through the steel floor.

With flat plywood you might not even feel the need to do that. Mine wasn't flat.
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Old 04-24-2018, 06:59 AM   #11
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I’m coming up on installing my new floor. I plan on having 3/4” insulation, framed with 3/4” wood in a grid pattern, and covered with 3/4” plywood with a thin laminate on top of that.

But how far apart should wood for the grid be? I’ve seen 16” thrown around for wobble factors, but I also think less wood and more insulation would be better for heating and cooling.

Thoughts?
We did a quickie/cheap remodel of a mobile home...we foamed boarded the floor...the only thing I'd do different is put framing to support the edges of the foam...they compressed, and we had to use floor leveling compound to fix that...no other issues
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Old 04-24-2018, 01:52 PM   #12
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Quote:
Originally Posted by TheArgobus View Post
I’m coming up on installing my new floor. I plan on having 3/4” insulation, framed with 3/4” wood in a grid pattern, and covered with 3/4” plywood with a thin laminate on top of that.

But how far apart should wood for the grid be? I’ve seen 16” thrown around for wobble factors, but I also think less wood and more insulation would be better for heating and cooling.

Thoughts?
Skip the framing and make your life easier and you minimize heat transfer thru the wood which while much lower than metal is much higher than insulation.
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Old 04-24-2018, 01:56 PM   #13
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Skip the framing and make your life easier and you minimize heat transfer thru the wood which while much lower than metal is much higher than insulation.
I'd have to agree here. My plan is to only have a frame around the perimeter of our living area so we have a good attachment point for the ply and to prevent the edges of the foam board from getting compressed.
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Old 04-24-2018, 05:57 PM   #14
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I'd have to agree here. My plan is to only have a frame around the perimeter of our living area so we have a good attachment point for the ply and to prevent the edges of the foam board from getting compressed.
You aren't going to be wlaking on the edges. The only exposed edges will be around the stairwell and it makes sense to frame there.
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Old 04-24-2018, 06:02 PM   #15
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You aren't going to be wlaking on the edges. The only exposed edges will be around the stairwell and it makes sense to frame there.
Good idea.
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Old 04-24-2018, 06:05 PM   #16
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You aren't going to be wlaking on the edges. The only exposed edges will be around the stairwell and it makes sense to frame there.
That's true, but I will have cabinetry, the shower pan, etc. I was groomed from childhood to build things to be indestructible.
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Old 04-24-2018, 06:18 PM   #17
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That's true, but I will have cabinetry, the shower pan, etc. I was groomed from childhood to build things to be indestructible.
I get that, but look at the numbers first.

If you have the base of a wall, let's say you make a shower wall from 2x4 lumber.

So you have around 34" by 3.5" as the bottom plate of the wall.

That's 119 sq in and it can take almost 3000 lbs of weight before it reaches the compressive strength of the foam.
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Old 04-24-2018, 06:41 PM   #18
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I wonder why so many are concerned with the compression rate of the foam board. Once it's covered with whatever wood flooring is going over it the compression rate of the foam becomes moot and now has the compression rate of the foam and the upper board. There's almost nothing you could mount in the bus at this point that is going to have any measurable effect on the foam underlayment.
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