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Subfloor - rib height dilemma

22K views 31 replies 13 participants last post by  orton  
#1 ·
I have finally found some time to begin working on my conversion! Installed a Maxxair fan and backup camera this weekend, as well as ‘mocked’ up my van layout using cardboard. I am now ready to start on the floor. I realize that subflooring has been extensively talked about on this forum, but after my searching around I still have some questions. In order to save headroom (can currently stand in MR with a few inches to spare) I have decided to go with ½ inch plywood on top of floor ribs (followed my underlayment then flooring- either vinyl or cork). What I am undecided about is what to use between the ribs under the plywood. I have seen that most folks use ½ polyiso or plywood, both of which are slightly thicker than the height of the ribs. To me, this seems to defeat the purpose of having a level surface to lay the subfloor on. Maybe the foam board will compress some to “even out”? I have also seen where someone has cut 2x4’s to the exact height of the rib (3/8”?). This just seems like too much work. Does anyone know of something (wood, plastic, etc.) that is the exact height of the rib?
I am really not concerned of the insulating properties below the subfloor and do not plan on screwing the plywood down (will likely bolt down using tie downs). However it seems as though I will need something between the ribs in order to prevent warping, especially between the wider gaps of the ribbing.
 
#4 ·
I ended up buying a marine grade piece of 3/8 inch plywood ($90 yikes) only to rip into many strips on a table saw. I then glued those strips to the van floor using construction adhesive. I figured 3/8" plywood + a little glue will perfectly match the height of the corrugated floor, and it does. I went with Marine grade plywood for it's durability if ever exposed to moisture and it's 7 ply which should provide enough meat to hold a screw. Only time will tell.

I did this on saturday and the glue is still curing under weight. The next step is putting a layer of 1/8 MLV, then 1/4 plywood screwed into the strips, and finally the vinyl top layer. I went with a coin-mat vinyl that I cut to size out of a 7.5 x 17 foot roll.

My goal was to create a low profile floor that provides a quiet ride.

My installation is very similar to morey's which is documented on his website (thanks Morey!).
 
#6 · (Edited)
The next step is putting a layer of 1/8 MLV, then 1/4 plywood screwed into the strips, and finally the vinyl top layer.
I too am trying to keep a low profile floor and am curious as to how the 1/4 plywood works for you. I haven't considered that option. Also, I like the idea of using MLV! Any ideas on where to get a good deal on that? I just read where another forum member removed the felt backing from the stock vinyl floor...would this essentially be MLV? If this would provide similar sound dampening as 1/8 MLV, I may go this route..and it is already cut!
 
#5 ·
Thanks for the input! Good to hear that the foam board will compress enough to even out. It seems like that would be the easiest material to use. Especially since I am not planning on screwing the plywood subfloor down. Although I will have to look into the Minicell foam option!

Regarding the marine grade plywood, I'm not sure that I would be able to find that locally.
 
#18 ·
Hmm..yeah I guess that would work. I'm having a hard time believing that I could keep a consistent 3/8 thickness that way though. I'm going to look a little harder for a material that will work (ie. 3/8 thick and hydrophobic), or just go with slightly taller rigid foam.

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#23 ·
It seems to me that the 1/2 rigid cheap foam should compress nicely. Don't get the denser purple/yellow/pink kind, just the foil on one side white kind.
 
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#25 · (Edited)
I went by Lowe's on my way home to see what they had as far as insulation goes. They have half inch Polypro which is foil lined on one side and very squishy. It is a rather large cell foam that is much like the styrofoam in disposable coolers. While I think it would work it only seems to compressible. In fact the three-quarter inch I'm able to easily compress in half with my fingers. They also had half inch R-max r matte plus-3 which is foil lined on both sides and a much smaller closed cell foam and still compressible, much more compressible than the more expensive closed cell foam. It's only about $11 for a 4 by 8 and I really think it'll work well. I'll check back in after I buy sheet and let you know how it fits.

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#28 ·
I use a very sharp knife with a thin blade and a long straight edge. I've done beveled cuts by using a block of wood to set the angle of the knife blade. Note, the knife's cutting edge must be beveled to both sides, not just sharpened from one side. This makes it easier to cut a straight line.
 
#29 ·
I'm planning to install cork planks floor and have the same question about ribs.
Planks are about 3/8 think and I'm trying to save height.
I'm wondering would 3 layers of 1/8 cork for rib valleys, plus 1/8 cork undergarment layer on top of entire floor work to install planks on it?
Would it work without layer of plywood? Probably I'll glue some wood blocks in places where no ribs and wide valleys, because I guess cork alone might be too soft?
 
#30 ·
I had the same issue and decided to use 1/2" poly board and used adhesive sound deadening material on top of the 'bumps' which are now flash with the foam. I plan to glue a 1/2" plywood on top of that and then laminate or cork. I need headroom and don't care too much about floor insulation. Saw some people use 2" of foam board etc. I live in the Northwest so temps don't drop too low.
 

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#31 ·
I’m doing three eights inch mini cell in strips in the valleys, and then a whole sheet of 3/8 inch mini cell on top of that. The ridge height is actually .4 inches, not .375, but close enough. I’m doing half inch plywood on top of that, but you could probably get away with 3/8 inch without noticing any dips. If you were doing cork plank I’m guessing it would appear uneven. So my total floor height above the ridges is 7/8 of an inch.