Sub-floor Prep

Exterior Shell, Sub-floor

Now that the trailer has been completed, we have started what we’ve been fondly referring to as “The Real Build”. The anticipation to start working with wood has been high, and we got our first taste of it on Friday, August 28th. It took us nearly 9 hours to install the wooden rails around the outside perimeter of the main frame of the trailer. These rails will provide a nailing surface for our plywood sub-floor and the bottom plates of our studs. IMG_20150828_153023I have to say, it was really enjoyable! Wood is a DREAM to work with compared to metal. Even though we were still attaching wood to metal, it was the wood that we were manipulating and levelling, and what a difference!!!

The first thing we did was spend about 10 minutes levelling the trailer from all four corners using our 2-ton scissor jacks, and then we were ready to get at it. We used 2″ self-tapping screws to go through the 1.5″ of wood and 1/4″ of steel, and staggered each screw 1′ apart along the length of each piece of wood. Alternating our screws from a higher position to a lower position, with respect to the centre line of the wood, prevented the creation of a single axis of screws along which the wood could curl and potentially crack, over time. IMG_20150828_183357Our purchased plans said to place screws every 2′, but this didn’t seem sturdy enough to us, so we went with the 1′ intervals. The imperial system is still driving me nuts, but on top of that, I find it so irritating how the measurements of wood are not even true to their imperial names. 2″ x 4″ wood in reality is actually only 1.5″ x 3.5″. AND, any given piece of so-called 2″ x 4″ has a better chance of spouting maple syrup than it does being actually straight! Rant over….

It wasn’t in the plans we bought, but it was mentioned to us that it might be wise to use a cushioning / water barrier material between the wood side rails and the metal of the trailer frame, as well as when we’re laying down the plywood sub-floor. I brought this query to the awesome facebook group “Tiny House People”, where I got a resounding “Yes!” to this question. So glad that we decided to do this. I’ve already complained about how wood isn’t straight, but we didn’t really take into account the fact that even though our metal should theoretically be flat, after painting, the surface was a little uneven due to drops of paint having dripped down and hardening into little convex ridges here and there. We picked up a roll (in the range of 80′) of 6″ sill gasket, and wrapped it around the entire exterior perimeter of the trailer frame in one continuous piece, sandwiching it with our 2″ x 4″ wood rails as we went. It filled any gaps between the two materials, creating a nice tight seal. This stuff is basically composed of a squishy, white, open cell foam sheet.

Before we could start attaching anything, Tim notched out cylinder shaped channels in the wood where it would line up with our welded-on threaded rod. We didn’t really have the right tool for the job… I think a router would have worked well. But we had a grinder, so Tim marked lines showing the needed width of the grooves and just ground out the wood with a wheel on his grinder. Not perfect, but it worked.

C-clamps are now my very best friends. They are amazing. If there’s a bow in your wood, or it’s twisted in any way, they are there to reduce the amount of profanities used and make your life generally easier. Self-tapping screws however… we’re not as good friends. I’ve heard you can buy ones that actually work, but ours were a big sham. Somehow, the very first one went in ok, but after that they kept breaking so we had to drill pilot holes.

We bought a box of 100 screws, and ended up having 5 left over. Sunk a few additional screws around the pieces of welded-on threaded rod, to bring the wood as tight as we could around those, as well as any other places that needed a little extra coaxing to be tight and straight.

In addition, we made the realization that our trailer is actually about 3/4″ longer than expected! We measured everything and it turns out that the 24′ pieces of HSS from the mill were slightly longer than spec. Never even considered that could be possible! Haha. The wooden 2″ x 4″s come in 10′ and 8′ lengths, so we needed two 10s and an 8 to flank each side of the trailer entirely. With the newly discovered discrepancy, this meant we had a little 3/4 inch gap between the tail piece and each side rail. To accommodate, we cut two small blocks and hammered them down into each gap and screwed them in from the end. No biggie.

I feel terrible writing about all of this next bit, it will be such dull reading. But, I’m afraid if I don’t write it down, I will forget the small details if we do this all again someday. If you’re curious about the specifics, read on! If not, stop here 🙂



The process of sinking each screw went a little like this:

  1. Place the sill gasket against the metal trailer frame with left hand, then hold the 2″ x 4″ wood against the sill gasket with right hand. Tighten clamp around the whole thing. Your partner does the same thing at the other end.
  2. Take a measuring tape and stretch it the length of your 2″ x 4″. Mark a vertical line with a pencil at each 12″ interval, making sure to have the two end screws 2″ in from the edge of the wood, regardless of where the nearest 12″ interval lies. Mark a horizontal line at each interval, 1″ down from the top or 1″ up from the bottom, alternating, creating a zig-zag pattern. The intersection of the lines at each position will be the home for each screw.
  3. Make sure the top of 2″ x 4″ is flush with the top of the metal using a combination square and a level, so that the plywood sub-floor will lay flat across them both.
  4. If the situation isn’t level, use a rubber mallet to hammer up or down on the wood, whichever is necessary, on the outside of the clamp. Doing this allows small increments of change in the position of the wood, all the while keeping it snugly in place thanks to the clamp.
  5. Drill a little piece out using a 1/2″ drill bit, to a depth of about 1/8″ to 1/4″, giving a space to counter sink the screw head. This way, the heads of the screws won’t be poking out making it impossible to get our sheathing and siding flat against this wood down the road. Pro tip: wrap some painter’s tape around the tip of the bit, making an edge so you know exactly how deep to go when drilling. Don’t want to make these too deep.
  6. Drill a pilot hole through both the wood and the metal so that your “self-tapping screws” (i’m convinced this concept is a sham) will go through without getting worn down or snapping off. We used #10 screws, which have a shank diameter of somewhere around 13/64″ (imperial, whyyy???) so we needed the pilot hole to be smaller than this. I think it was something like 9/64″.
  7. Sink your screw, at last. Move clamp further down the line.
  8. Repeat


5 thoughts on “Sub-floor Prep

  1. Hi!! My name is Elizabeth Gough, an ETL at Target in Maryland, and my boyfriend David, grad student for Physical Therapy are currently in the research/ sketchup phase for our Tiny House.

    I have visited, researched, and watched countless episodes of people with tiny houses on Youtube and my boyfriend (soon to be fancy fancy fiancee) and I are sold on the idea!!

    I have read your entire blog, and i feel very attached to it–alot because of your detail, and partially because I can relate to you in many many ways.

    This is all to say I have questions I would love to get your input on.
    – How did you construct your plumming/electric?
    -What utilities are you using?
    -what has your budget been?
    – How are you building your loft?

    Thank you so much for your well written blog! Know it has been a lot of help to me!!!
    I hope to hear from you soon!



    1. Hi Elizabeth!

      I’m deeply sorry for leaving your lovely comment unanswered for so long. We moved to Japan in January of this year, and I really haven’t done any work on the blog since then. Our tiny is stored in a warehouse until we return in April 2017, at which time everything will continue.

      Let me start by saying thanks so much for the compliments and support! It is so rewarding to hear that my writings have been of use to someone 🙂 As for your questions:
      -We have not yet installed the plumbing or electric. Both will be adventures to embark on this coming summer. I’ll be sure to write in detail about them!
      -For utilities, we plan to dig a well, and to connect to our local electrical grid since in Newfoundland, the large majority of our electricity comes from hydro-powered sources (sustainable). We’ll use a combination of electric and wood for heat. I can’t wait to get our tiny little wood stove!
      -We plan to make a summary post regarding the budget at the very end, which will be itemized, and separated for the exterior and interior phases. Stay tuned!
      -The plans we bought from detailed the process for building the lofts. We will be writing about our experience when the time comes for sure.

      Have you started your tiny house build, and if so, how far along are you? Hope to hear from you again soon!
      Jess and Tim


  2. Thanks for the detailed post. My boyfriend and I are starting this process today eek! Keep up the great blog 🙂


    1. Your welcome annmarie88intern!
      Hope your roof build went smoothly and your tiny house progress has been enjoyable! You’re probably well ahead of us now, we took a year off to live in Japan and practice tiny space living in a country that has totally perfected it. We feel ready to come back and continue now! Thanks for the support 🙂


  3. Hey quick question! You basically made your trailer frame your subflooring as far as I can tell? I’ve seen this method a few times and would love to do it also! But are you worried that without the standard lumber subflooring there isn’t enough of a “flex zone” for movement?
    Thanks so much!


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s