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Discussion Starter #1
Hey all!

Planning my first build, reading a ton, and have a rough idea for my floor and ceiling layers. Wanted to run it by the experts :)

I'm 6'2" so need to be really mindful of height usage. Here's what I'm thinking:

Floor:
  • minicell in grooves
  • 1/2" minicell
  • 1/2" plywood
  • 1/8" vinyl sheeting
Ceiling:
  • Spray foam insulation up to the ribs with light coating on exposed metal
  • 1/2" plywood

Ideally, this all nets a tad under 2" total thickness, allowing me to walk about the cabin.

Would love any feedback, especially from any tall folks :)

- Biko
 

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Forget the minI cell, especially in the groves, no need to put anything in them. Use ½" Polyiso directly on the steel floor and ½" hardwood (poplar is great) over that. You don’t need to glue anything down on the floor simply use the existing tie down locations (you may need to get longer bolts at Lowe’s or HD). paint both sides of the plywood with Kilz,or something similar befor laying it down to prevent mold, etc. The ⅛" vinyl sheeting is great you only have to glue it down on the edges if you want. The spray foam on the ceiling is good but very messy, you can simply use the same 1/2" polyiso on the ceiling and fill the cracks in with foam.
 

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We have about 73-3/4" headroom in ours right down the middle, a little less toward either side. Our floor is 1" poly-iso, 1/2 plywood, 3/16 vinyl; ceiling is 1/8 baltic birch over 3/8 stringers fore/aft.

Our ceiling is insulated with 1" poly-iso foam board glued to the van sheet metal with GreatStuff Foam. It's flush with bottom of the roof ribs (no height reduction). The walls are 1" poly-iso + GS Foam, as well. See Shiny's build thread linked below.
 

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Your idea would give you 2 more inches than I have. I did 1" polyiso on the floor, then 3/4" tongue and groove, then 1/8" vinyl. My ceiling is 1" strips on ceiling ribs, then 1/4" tongue and groove planks over that. I am 6 ft and it is fine. So, if you did what you mention (I agree with KOV on the grooves and 1/2" polyiso), then it should be the same room I have now.
 

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Go with something thinner than 1/2 plywood on the ceiling, that is just way more than you will need or want. I used 5mm plywood and probably could have gone thinner if they had something else in stock at the time. You do want something ask a thermal break between the ribs and ceiling, so the light coating will work if you go that route, if now a layer of something like EZ-cool just to serve as a thermal break would help.

I agree with everyone else, no need to fill the ribs in the floor. A 1/2 sheet of xps or polyiso can support 10x more weight than the promaster can carry even though only 1/2 of it is in contact with the floor ribs. The compressive strength of polyiso is about 20 psi, 50% of a 48inch x 96 inch polyiso board is (.5x48x96) 2304 square inches, for weight bearing capacity of over 46,000 pounds. Which is slightly more than the promaster can carry. In any event you gain almost nothing by filling the ribs in terms of insulation since the air space is trapped air anyway, save some time and money and skip it.
 

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Agree that 1/2" ply on ceiling is too thick, too stiff, & too heavy. Remember that ceiling fan & roof AC control knobs intrude into your clearance up to 1.5"
 
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