T42 Subfloor & Bottom Plates

Day 2. Subfloor & Bottom Plates. Done! Earlier this week we kicked off our first T42 Build Blitz. We made good progress on Monday with the T42 Undercarriage & Floor Insulation. On Tuesday we had another gorgeous day down at Green Anchors and Build Blitzers Andy and Sonja worked with me to install the subfloor and bottom plates. (More photos to come. Having photo upload issues. Grrr!)

We started out Build Day #2 by marking the center line of our trailer. To do this we measured the trailer width in five points across the trailer, marked that center point, and drew a line the length of the trailer. Then we laid out our bottom plates, making sure that they will accommodate our SIPs layout. We cut our bottom plates to length and then held the tape measure to the center point and adjusted our bottom plates side to side so that the outside of the plates were 49 1/2" from the center in each direction and clamped them in place. The trailer is 100" wide and the house is 100" and the SIPs have a 1/2" outer skin, so laying out the bottom plates this way gave us 99" from edge to edge which should accommodate our SIPs just right. We did the same front to back and we ended up a schosh bigger in this direction, but it's only 1/8" and in my experience tiny houses often grow a smidge from the plans, so we think it will work okay.

Then Andy drilled through the bottom plates from below using the existing holes. Our trailer had the holes pre-drilled in the flanges, which saved us heaps of time! (Though we did have to drill two more because of the way our SIPs lay out. Andy did that using a set of bits that stepped up 1/8" each time. Thanks, Andy!) Then we inserted our 4" long 1/2" diameter galvanized bolts, using a flat washer then a plate washer on top of the bottom plate and a flat washer, lock washer, and nut below the trailer flange. Unfortunately, the plate washers I'd picked up at the hardware store (which are actually 3" bearing plates from the Simpson fastener section) hung over the edge of the bottom plate, so at lunchtime I swapped these out for 1 1/2" plate washers.

Once the bottom plates were in place we double-checked the span for our subfloor. Our subfloor is 3/4" tongue and groove Edge Gold which sits on top of the polyiso foam and the sill seam on top of the trailer. We cut the subfloor with enough of a gap all the way around that the SIPs will be able to sit down nicely onto the sill seam. We tacked these subfloor pieces down with self-tapping screws along the perimeter of the metal trailer frame. Then Sonja sealed the seams between panels with another bead of sealant. Once the SIPs walls are up we'll be able to close the joint between the walls and the floor by adding a bead of spray foam if necessary and then a sealant joint. This isolates our wall system from our floor system. We never have the subfloor in contact with the elements outside, transferring cold to our feet. (I did it this way for The Lucky Penny Floor Box, too.)

We got the floor system nearly finished by the time we took a late lunch. After lunch we installed the new plate washers, double-checked our measurements, and cinched down the bolts (but not too tight!) Sonja also plugged the extra holes in our trailer using black 3/4" PEX plugs and more of that handy sealant. (The "extra holes" were pre-drilled through the sides of the trailer for that wooden floor system we didn't use - see my note in T42 Undercarriage & Floor Insulation for more on that!)

With the bottom plates bolted down and the subfloor in place, the trailer is now totally ready for its trip up to Premier SIPs in Puyallup. Patrick of Artisan Tiny House will be making the drive with me to pick up the SIPs early next week. (and I get to go on a field trip of the SIPs factory!) I'm so excited!