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Tiny House Subfloor Design with Extra Insulation

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Hi All, so hopefully this picture is clear enough (click for largest version).  I’m finalizing my trailer design for a house that we hope will be sufficiently warm in cold climates.  In order to get extra insulation without sacrificing too much head room, i’ve tried to get a few extra inches of insulation between the trailer wheels while also getting some out to the extents of the trailer’s edges.  As indicated in the drawing, i’m planning to cover the underside with galvanized flashing and a moisture barrier.

My biggest question is whether or not the bolts that are running through the main frame members of the trailer (the ones at the lowest elevation of the 3) are too close to the edge of the 2 x 6 lumber and at risk of tear out?  I’ve tried to find ways to calculate the forces/stress here but to no avail.

Tiny House Subfloor Design with Extra Insulation

More broadly, am I missing anything big in this design and/or making this more complicated than it needs to be?

Thank you!

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{ 11 comments… add one }
  • Mike
    June 1, 2017, 8:17 pm

    This looks a bit too heavy and a few issues (imo)…

    0. Don’t use OSB for anything structural- period.
    Why OSB? It’s horrible when it gets wet. How are you protecting it?
    Better to use exterior glue plywood.

    1.The overhang area (from the main frame to the wheel) the pair of 2×3 with the bolt between them- should be stacked not side by side, otherwise they’ll split. Should be in compression- wood works better that way.

    You can eliminate the 2×3’s altogether by getting a few joists a few feet longer and notch them

    Also that 4″ angle is going to be too heavy for that piece of panel hanging there- better to weld it the the metal frame with a plate if you want it out that far- or better just bolt it to the frame and let the panel hang over. (not load bearing right?)

    2. You do not need a panel that thick on the bottom of 2×6 joists. Your panels on top of the 2×6 joists will distribute the load fine. Use a heavy plastic sheet on the bottom, for moisture protection, like they use in RV’s.

    If you eliminate the 21/32 panel under the joists, also remove it from the overhangs and use the extended joists I mentioned above…

  • Jeff Built
    June 1, 2017, 9:00 pm

    Over complicating the issue. Can’t imagine an “event” that would tear out like you fear that would also leave your home vertical.

  • Robert Aulicky
    June 1, 2017, 9:01 pm

    If I understand the picture the OSB is supporting the angle iron? If so stop. There is absolutely no strength in OSB. Trailer manufacturer would have made the plate to support the walls.

    • James D.
      June 2, 2017, 4:02 am

      Agreed, you can’t have load bearing walls go up over a non-load bearing foundation and the trailer is the foundation for a THOW…

      So, unless that drawing is just missing some of the details of the full steel chassis of the trailer then that’s not going to work…

      • Alex
        June 2, 2017, 10:24 am

        Thanks for the input guys.

    • Robert Aulicky
      June 12, 2017, 12:49 pm

      Okay I read your post back and possible the simplest thing to do is put sleepers on the metal frame to make up the distance of the dropped cross members that were for the 2 x decking bring the height even. This would be your insulated cavity, remove the OSB. Put pans under there instead and deck with a tong grove approved decking. Done! While installing the walls use hurricane straps to the steel frame to the stud or steel brackets and bolts. Wind lift and thrust. 100-150mph.

  • dana
    June 1, 2017, 11:08 pm

    i agree with Robert, above. …
    if it is too late to have Trailer Mfr install, then find a supplier for angles that can get you a longer leg….a 4×4 could be replaced with 4×6, or 4×8 (longer projecting leg), which would allow you to attach the angle to the trailer, to support the sub-floor (instead of asking the floor to support the trailer).
    a structural engineer, can make a recommendation based on loads, or even perhaps the steel fabricator.
    the insulation you use is critical to the long term.
    1″ of EPS foam has a higher R value inch per inch than fiberglass or other traditional insulations. good info here: http://insulfoam.com/insulation-comparisons/ note, please that all foams should be covered with drywall or other solid covering to prevent chemical/toxic laden smoke from entering compartment.

  • Trevor
    June 2, 2017, 8:21 am

    Agreed that 4×4 angle is suitable if it’s competently welded to the main frame via gussets or HSS tubing.

  • thewanderingsquash
    June 4, 2017, 7:11 pm

    Hi All,

    SO Sorry that I haven’t replied until now. This was my first post and it took a few days to go up – I probably tried to post this 15 times because I didn’t see it show up on the site right away. Now I know!

    Anywho – thank you all for the feedback. I realized in hindsight that I left out an important detail in the drawing; the 4″ Angle Iron is in fact welded to the frame with 2×6″ rectangular tube outriggers every 24″. I think I’ll have plenty of support for the walls (but please tell me otherwise). I’ll definitely take the other pieces of feedback (Ply instead of OSB, notched trusses etc) into account during the build.

    Thank you again for the help!

    • June 12, 2017, 12:37 am

      We have the most widely used, proven, engineered tiny house foundation that solves the issue with sheer loads on your project. Call our home office to speak with one of the staff who can answer your questions live.

      Trailer Made Custom Trailers

  • Nigel
    June 5, 2017, 6:41 pm

    Looks overly complex. Tiny Nest (they have a YouTube channel) builders used an Iron Eagle trailer. Might want to check them out…I think that would solve your problems.

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