Subfloor: Days Two and Three – Zip Boards and Flashing


After successfully framing the subfloor of our house, we now needed to attach the zip boards and flashing to the wooden frame. Because of the way we planned to attach the subfloor to the trailer, we had to build our subfloor upside down. At first this made no sense to me, but Drew explained that because we needed to bolt the subfloor to the bottom of the trailer, there was no way to lay down the aluminum flashing onto the trailer, then attach flashing to the zips, then all that to the framing and keep it all square. Remember, we have to bolt the entire framing to the trailer in 40 spots with 1/4″x 4″ lag screws. So it turned out that the easier (yet heavier) alternative was to build the whole thing upside down, flip it, then put back on right-side-up and continue from there.

Sounds easy, right?

No, no it doesn’t at all.

So we first started working on the zips boards early Tuesday morning. Zip boards are basically plywood sheets coated on one side with a waterproof coating. We decided to use this on the bottom of our house, and to also include a level of aluminum flashing for extra protection. Water is a big concern in tiny houses, especially since the bottom is not on the ground. And if you’re driving in the rain with your house, you’ll certainly want extra protection. Plus, bugs and other critters might like to find their way in and make their own tiny homes within the insulation.

Cutting the zip boards took a lot of fine tuning to make them have a snug fit.

So first went the zip boards. We cut one to the right size, marked where the nails would go, and then nailed every 3 inches around the edges of the board. Then we nailed every 8 or so inches across the beams. Even though we were using the palm nailer, which albeit is faster than a hammer and nails, nailing the boards still took a while. So Drew and I decided that I would nail the boards while he worked on cutting them. I was glad that we were able to divvy up the tasks like this; it made the day go by faster and the project much more efficient. In the picture to the left, Drew is using a jig-saw, which is easy to use and lightweight, but leaves a more jagged cut because the blade is very thick, and because the cut is directed by your hand, which doesn’t have the best sense of straight lines. It was however convenient.

Our brilliant tarp contraption.

One thing to note is that there was no shade on our job site, and we were facing 84-degree days in direct sun. While we had a tent, it didn’t cover the entire site, so we decided to get creative. We took the tarp we use to cover the trailer and covered our workspace by attaching it to the fence and draping it over our tent. Kind of cool, huh? And it worked! It only fell once. I consider that a win.

Attaching the zip boards took a lot longer than we thought. It was late afternoon by the time we finished that part. Luckily, our friend Evan came by and was able to help us with taping our zip panels (they make a special zip board tape to cover the seams) and then with the flashing (which they also make a handy-dandy tape for). We managed to get the whole thing taped (but not nailed), right before dark. Then we called it a day.

Day Three:

The following morning, Drew finished nailing and taping all the seams (and nails) of the aluminum flashing. All was secure. Now for the hard part – flipping the entire thing over. Not only that, but we couldn’t just put it back onto the trailer – we first needed to drill holes into the steel trailer so we could screw about 40 bolts into the framing to secure it to the trailer (which we didn’t think of doing earlier). So the plan was to take the built subfloor off the trailer, turn it over, and place it on the ground. Then we planned to drill the holes and put the whole structure back onto the trailer. Once we finished that, we could continue with securing the subfloor and stuffing it with insulation.

Since we needed to lift an entire wooden frame covered in plywood and flashing, we needed reinforcements. We considered enlisting the patrons of a nearby gym, but thought they were closed, so we instead enlisted Drew’s family. We ended up with five people. Thus the maneuvering adventure began!

Right near the ends of the wheel-wells are where the 4-ish nails are holding the three subfloor structures together. If those bend, the whole structure could come apart.

We threw around several ideas how to do this. One thing we were especially concerned about was racking or twisting – remember the three sections we had built in the framing? They were all attached to the middle section by about eight nails (we later added a few screws to help secure it). We were afraid that if we lifted one side the whole thing would tilt and twist and fall apart.  With that in mind, we decided to try to lift and place the entire structure onto sawhorses, so that the next day when we needed to lift it again, we wouldn’t need to lift all the way from the ground. In theory this worked great, but when it came time for us to lift the heavier back end part off the ground, we couldn’t do it with just five people. Remember, we needed to flip it over as well as move it. So we ended up laying the whole thing on the ground right next to the trailer. Unfortunately we don’t have any pictures of this event, since we needed all hands on deck. But it was quite the sight, believe me.

Lit by a floodlight, Drew drilled holes into the trailer well into the night.

After Drew’s family left, Drew, Evan and I decided to continue working as best we could before dark so that the next morning we could enlist Drew’s dad and his associate Mike to help us lift the whole structure back onto the trailer. Evan and I installed cripple studs on the back part of the trailer so we’d have boards to attach the flooring plywood to the next day. Drew went ahead and drill holes all throughout the trailer. We went past dark, and ended up working til about 10pm. But we finished it!

Now for a 13-hour day starting at 8am the following morning…


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