Sub Floor Part One -Setting the Joists.

IMG_3349  In this post we will take a look at the sub floor construction. We designed and built for maximum strength as our house is designed to be lifted off the trailer, if we so choose.  With this in mind, we used a fairly serious amount of heavy hardware to anchor the sub-floor to the Foundation beams. This is a long post, so grab some refreshment and get cozy, or bookmark us and visit often!
Starting out:
We started by using a chalk line to carefully snap parallel lines over the foundation bracing while removing mason’s twine which I used to mark the proper location earlier. The foundation braces are staggered which allowed me to drive screws straight into them as I was laying the foundation, instead of toe-nailing, We snapped side-by-side lines, and marked where the boards traded off.  Then using tape and measure, we clearly marked where the corners of each cross-brace lay under the floor guard and OSB.  Taking care to avoid the ends of the boards beneath as much as possible I drove 100 additional 1.5″ screws through the OSB and floor guard for additional sheer force resistance. I wouldn’t care to come sliding loose on the road.
The Big Wood: We used seven long beams as the basis of our floor, each was a picked 20′ long piece of Doug fir. Obviously these beams had some crowning and not a small amount of warp over a 20′ span.    We trimmed them to fit inside a header beam at each end with a skillsaw, then applied a copious amount of Locktite™ PL400 subfloor glue to each face to be joined spread evenly with a putty knife. Then we set them lightly in place as true as possible over the OSB.
Use the Warp, Luke:  In the picture above, we are securing the Ledger board to the  edge of the subfloor. To overcome the warping, I used the smaller light and medium strength angles and a combination of 1″ joist screws and Stimpson Strong Ties™ 1.25″ structural bolt #8 to hold the long pieces at critical junctures, Then I used a medium pipe wrench to literally hold the boards in position at the ends by main force, while my wife drove Deckamate™ 3.5″ screws home through  guide holes with an impact driver.  Of course they are still twisted at this point, but at least laying crown up, flat as possible and roughly squared to the head beams….Whew!
IMG_3320 Board Wrestling: Next, I reinforced the long beams to head beams at either end with Medium Stimpson Strong Ties™ angles with three 1/4″ openings on each face, as seen in the picture above. I used standard 1/4″ x 1″  zinc plated interior Lag bolts to join these.  As usual I drilled guides for everything. Using heavy clamps and carefully trimmed wood blocks driven into place with a rubber mallet to hold the beams exactly where I wanted them. More heavy clamps and more wrestling on the ledger boards, which could not be braced. Finally all were in place and more square then I had any right to hope. two of the long boards in particular were twisted pretty severely, even after carefully stacking and curing them for a few weeks with adequate spacers. I positioned these boards on either side of the middle, and used my straightest, truest boards as the ledger boards and in the exact middle. Here’s where those woodblocks mentioned above could be adequately braced on the other beams to literally force these twisted boards into a mostly true configuration. Later on, as I placed the cross bracing I was able to true them up even more by literally driving each carefully squared brace into place with my rubber mallet. As you may deduct, this was physically and mentally very challenging, and would have been easier with extra skilled hands. DIY can be a surprisingly effective way to burn calories 🙂
IMG_2918 IMG_2917
More Heavy Metal: The pictures above compare the main fastening bolts we used to the edge of a foundation beam to give you an idea of whats happening here. How are we keeping the house from sliding off the foundation? We used heavy 3/8″ x 4.5″ galvanized bolts to pierce through the OSB overlay, the 20 gauge galvanized Floor Guard, and anchor deeply into the foundation boards.  Each bolt penetrates almost into 4″ into a 5.5 inch board. Remember that the OSB and floor guard already have a few hundred screws holding them down.
From Every Angle: We used a total of 19 heavy Stimpson Strong Ties™  6″ x”6 L-angles, as seen above. Each has 2 opening per face for 3/8 inch fasteners, for a total of Thirty-Eight 4.5″ bolts going into the foundation beams and braces. each also had 6 smaller holes that used zinc and structural screws to set in place to reice the larger bolt. Why 19? It just worked out that way. There were only so many places where the joists crossed the foundation where an angle would fit, and I did not want to run too many too close together for fear of weakening or splitting the long floor joists. or foundation beams. I did split one foundation brace, but was able to replace it.  Of course, each hole into the foundation is pre-drilled first with a small bit as a pilot, and then a larger bit,  just a hair under half the diameter of the bolt just as far down as the bit would go, roughly 4″. With the Angle and a heavy washer in place, only the last 3/8″ of the bolt bit into raw wood. I used 3/8″ zinc plated interior bolts and nuts with standard zinc plated washers to secure the vertical part of the heavy angle to the joist beam. These were drilled out to snug fit, and the hole was sunk enough to allow the bolt and washer to be flush with surface of the joist. I used a 1.25″ spade bit to accommodate the washer. Why? because we used solid core foam insulation later on, and I wanted to avoid notching or breaking it as much as possible. A snug fit makes for a warm house. I used a wooden mallet to set the bolts through the beam, as the holes were purposely snug. I also had to trim the last inch off the vertical arm of the angle, because my floor beams were 5.25 inches tall. My trusty angle grinder made short, if noisy work of that.
IMG_3307 So in the end, we used 19 heavy 6″ x 6″ angles to join foundation and sub floor, 14 Medium 3.5″ angles to join the long beams to the headers, and another 17+ assorted medium and light angles to hold the joists as in place, to accurately set the bigger stuff. I drove an additional 35 Stimson #8 1.5″ structural bolts from the the bottom up through the floor guard into the sub floor.  As I mentioned a few times: this floor is designed to withstand a sudden stop while towing or the incredible stress of lifting the house of the trailer.
430 Oh did I mention we used a PL400 on every surface of every permanent joint? Why???? All the chemicals, footprint… ETC??!? Why is because with a family in a small house a creaky floor could equal madness. So we used glue like crazy.  This also adds Crazy additional sheer force resistance; this glue really sticks 😉 The picture above is from later in the build, and these empties include some spray foam cans and premium glues used later on mixed in with the sub floor empties. I allowed 10 days of curing and out-gassing before we started laying in insulation, and it was another week or more after that before the top sheathe finally went on the floor,


2 thoughts on “Sub Floor Part One -Setting the Joists.

  1. Pingback: Subfloor Road Guard | The Roots of our Tiny Life

  2. Pingback: Floor Top Sheathing | The Roots of our Tiny Life

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