The framing of the raised floor system was our first true construction task for the tiny home. We went to Menard's and hand-selected each piece of 2x10" lumber for the beams and joists, each sheet of 7/16" OSB (oriented strand board) for the sheathing at the underside of the floor frame, and each sheet of 3/4" OSB for the floor finish.
Our construction strategy involved building the entire floor framing in three large sections on the ground and then lifting them into place on the trailer frame, where the sections would be bolted to each other and to the trailer frame itself. As shown in the series of photos in the blog post below, this strategy allows the framing to be easily maneuvered for squaring and nailing, and allows the underside sheathing to be screwed into place from above.
As trained architects, we are very familiar with making precise and well-crafted objects, and we are reasonably familiar with power tools and the design and coordination of structures and systems; however, the framing of the first floor section proved that our familiarity with construction techniques and tolerances was considerably lacking. After all the framing lumber was cut to size according to our digital model, our first construction hurdle involved getting the framing squared. For this we ended up using a metal angle and some temporary bracing, as shown in the images above; the attachment of the underside sheathing, validated the squareness of the framing.
The 2x10" framing members were nailed together, while the 7/16" OSB underside sheathing was screwed onto the framing. The construction of the floor framing involved basic tools, such as tape measures, pencils, metal angles, and clamps, and power tools such as a circular saw, table saw, nail gun, and drill.
We first constructed the 4' bathroom section of the floor and then the 8' kitchen and entry section of the floor and lifted them into their respective locations at either end of the trailer. The 8' kitchen and entry floor section is shown in the middle two images above; the gaps in underside sheathing are for the water tank and battery bank storage compartments integrated in the trailer framing below the raised timber floor system.
The three images below show the construction of the final 12' floor section at the center of the floor system where the trailer wheel hubs are located.
The row of images below show the final 12' floor section being lifted and positioned onto the trailer. As made evident by the images, the floor sections were incredibly heavy and difficult to maneuver, requiring four people to relocate them from floor to trailer.
After getting the final floor section onto the trailer, we found it impossible to fit all three sections flush on the top of the trailer. This was the result of measuring and building the floor system according to our digital model, rather from the measurements of the built trailer; the trailer apparently had a few dimensional discrepancies relative to what we had specified in our drawings to the trailer manufacturer. This resulted in two hours of four strong men forcing the floor sections into place via jumping and sledge hammering, as shown in the right-hand images below. While this was exceedingly frustrating, it was admittedly equally amusing.
The biggest lessons learned in the framing of the floor were to check built dimensions, to build with tolerances, and that construction can be a bit messy and unpredictable, regardless of any amount of prior planning.
In the end, the floor framing was successfully installed, with each section squared and sitting flush against the trailer and against the adjacent section(s).
While some tiny homes opt to use the trailer framing itself as the floor framing, we chose to employ a raised floor system for a few reasons. Firstly, a raised floor system allows us to route plumbing and electrical through it. Secondly, nearly half of our raised floor system serves as under-floor storage, with all compartments 9" deep, and typically 30x20" in length and width; the remaining raised floor system compartments are insulated, with insulation for the in-floor storage zones located within the trailer framing below. Finally, the raised floor system, which is flush with the top of the trailer wheel hubs, allows us to avoid the trailer wheel hubs as an eyesore and impediment to efficient interior space planning. The greatest setback to the raised floor system is that it reduces the clear height of the interior volume; if we had opted not to have a 10" raised floor, we could've likely gained 10" in ceiling height, which would've been an enormous asset in the lofted sleeping area.