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Community and Q&A

Tiny house trailer sub-floor insulation

Michael_Kalman | Posted in Energy Efficiency and Durability on

Climate zone 5A/6A (around there). Building a tiny house on wheels. There are 1×3 cross members and I plan on flashing the bottom of these crossmembers with galvanized steel and building a subfloor on top with foam sill seal on top of the metal frame to prevent thermal bridging. I am wondering, do you think it’s fine if I caulk the flashing all around to make it air tight and then fill the cavities around the metal members with cellulose? Will the cold air from the outside make the semi warm insulation condensate in our -30 winters? I don’t plan on using a plastic vapor barrier but painting the bottom side of my top subfloor sheathing (3/4″ ply) with an oil based primer that is around 1 perm.

Or another option, should I just flash the top of the crossmembers, and build a 2×6 subfloor on top and lose that 3 inches of insulation? If I do this, will the metal flashing touching the bottom side of my subfloor potentially cause condensation?

Let me know your thoughts!

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  1. tommay | | #1

    At least use some foam insulation with reflective coating...

    1. Michael_Kalman | | #2

      Foam insulation results in a too low of a perm rating, hindering breathability, no?

  2. GBA Editor
    Brian Pontolilo | | #3

    Hi Michael.

    Do you have any drawings of this assembly to help us visualize what you are building?

  3. Jon_R | | #4

    Make sure that air can flow behind the galvanized steel. So it acts about like siding over a rainscreen, not zero perm exterior sheathing.

    1. Michael_Kalman | | #5

      How do I make sure the air can flow around the steel? Should I leave a 1/4" gap? or 1/8"?

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