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Discussion Starter #1
So I got my floor mostly finished. 1/2 insulation board and 1/2 birch ply. Followed a lot of the advice here. Looks great, fits well. I ran three 4' sheets of ply horizontally to span the 12' space, two have one of the factory tie down bolts, the other (middle) has two. Ran the insulation opposite so no matching seams.

I haven't glued the ply to the insulation but plan to use Great Stuff Construction Adhesive. There's a good amount of flex at the seams and some of the edges (sliding door edge especially). I'm hoping glue and a ton of weight for a day or two resolve much of it. If it doesn't, I'm curious about the following: use a router to recess a few narrow areas where the ply meets. Then, fill that mirrored recess (spanning both sheets) with a nailing plate, fastened with screws.

I'm using vinyl plank flooring that should tolerate that well.

I'd really like to avoid screws/bolts through the body of the van and wasn't sure if someone had tried this method before. I don't have any joining tools, so I'm a little limited on making the ply a 'single piece'.

Thanks
 

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This is one very good (but too late for you) reason to use ¾" ply!
 

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Discussion Starter #3
This is one very good (but too late for you) reason to use ¾" ply!
Haha, probably so. I'm a tall person, so trying to save all the height I can. I'd probably be seeing the same with 3/4", albeit a little less. I think (hope) I'll be OK once the ply is bonded with the insulation. I just don't want any major seam popping up and down with the LVT product on top. With fridge and cabs in there as well, should help.

No feedback on the idea, Keeponvaning? ;)
 

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Did you offset the seams of the insulation from those of the plywood? (So that the seams don't line up). (Edit, just saw that you did).

For the edges near the doors you can use a piece of 90 degree angled stainless or aluminum to strengthen it. It also hides the edge and stops it from getting all chipped up. I used heavier sheet goods (1" foam and 3/4" plywood), but I would caution against gluing everything down. It's not needed and may end up being a real headache down the road if you or someone else wants to make repairs or changes.

Maybe try a rigid plank flooring of some type to stiffen everything up?
 

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Discussion Starter #5
Did you offset the seams of the insulation from those of the plywood? (So that the seams don't line up). (Edit, just saw that you did).

For the edges near the doors you can use a piece of 90 degree angled stainless or aluminum to strengthen it. It also hides the edge and stops it from getting all chipped up. I used heavier sheet goods (1" foam and 3/4" plywood), but I would caution against gluing everything down. It's not needed and may end up being a real headache down the road if you or someone else wants to make repairs or changes.

Maybe try a rigid plank flooring of some type to stiffen everything up?
I did offset the seams and I'm planning a plank flooring. I could be overthinking it all as well...
 

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Youve got the right idea, but wood inserts glued in place would be better than metal plates screwed in. Better yet, make a groove down the centerline of the seam and fill with a wood strip. This would effectively create a lap joint and your floor will effectively become a monolith.

Many of us here know that 1/2” can make a fine floor.
 

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Discussion Starter #9
Youve got the right idea, but wood inserts glued in place would be better than metal plates screwed in. Better yet, make a groove down the centerline of the seam and fill with a wood strip. This would effectively create a lap joint and your floor will effectively become a monolith.

Many of us here know that 1/2” can make a fine floor.
I like that! Thanks.
 

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If I interpret your description correctly, I reinforced my 1/2" plywood butt joints the same way. That is, with a backing strip of plywood glued, screwed, and inset into the insulation. But I'd do it MsNomer's way next time.

BTW, gluing plywood to the insulation is overkill if you start with flat plywood then bolt it through the insulation to the van floor.
 

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Discussion Starter #14 (Edited)
You made your own SIP
SIPs | Structural Insulated Panels | Construction | Thermocore that’s quite a bit different than just laying ¼" plywood over insulation board!
I think that would have been 1/4 ply, foam, 1/4 ply. Would be stout!

I've wondered why some folks don't do two layers of ply (either like a SIP or right together cross-directionally) instead of furring strips... Would give a screw hold and probably a mighty flat subfloor. It crossed my mind when I was stewing on these seams.
 

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Discussion Starter #15
Put some weight on it. We shall see in the morning if anything else is needed.

Btw, this forum rocks. Cheers everyone.

66502
 

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Biscuits or spline the joint and you will be fine with it glued well. I personally would go with biscuits as they are super easy and you can use just about as many as you want.
 

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I think that would have been 1/4 ply, foam, 1/4 ply. Would be stout!
I've wondered why some folks don't do two layers of ply (either like a SIP or right together cross-directionally) instead of furring strips... Would give a screw hold and probably a mighty flat subfloor. It crossed my mind when I was stewing on these seams.
SIPs are used for walls and similar structural applications to carry loads with fewer/no intermediate supports (studs, etc). The van's metal floor provides virtually continuous intermediate support. So there would be no structural benefit. Granted, it would help flatten the floor, but the positive experiences of so many folks here with one layer of plywood (glued or not) indicate a SIP sandwich would be overkill. Additionally, layering two sheets of 1/4 plywood on top of each other requires 2X more plywood than a single layer of 1/2 with edge jointing. More importantly, the layers in a sheet of plywood already alternate direction, so two 1/4 sheets will not be as strong or rigid as one 1/2 sheet unless you glue them together to make them one. But, hey, I'm guilty of unnecessary investments in over-engineering myself. It's kinda my jam ;)
 

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Mine is 1/4 inch plywood glued to the top of the 1 inch polyiso and then the bottom of the polyiso glued to the metal floor -- all using Great Stuff as adhesive, so it does make a sort of sandwich or SIP panel with the plywood as one face and floor as the other face. That was not really my intention when I did it, but it is very stiff, lightweight, and servicable - and no squeaks.

Only negative I can see is it will take a bit of work to get it up if I ever need to replace it.

Gary
 

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If it still flexes at the door entrances, you could cut the insulation back 4” or so and lay in a piece of wood there. I did my floor that way, and it’s as solid as a rock.

For the seam... I’d consider creating a lap joint by routing 1/4” all the way across the seam, about 2” wide on each side, and lay in 4” x 1/4” plywood with glue. Also, about the SIP idea... I affixed the polyiso insulation to the plywood with leftover gripper paint from the box store, and it’s very strong, so that’s a fairly cheap augmentation to the strength.
 

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2” would be great, but he’s going to have a hard time finding a bit that wide, if it exists, and I wouldn’t recommend it anyway because it would be so hard to control manually. My bit was either 1/4” x 1/4” or 3/8” x 1/4”. It’s plenty.
 
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