Several people have already asked me why I bothered installing a new subfloor over the existing plywood. The primary reason has to do with the removed side walls. When the sidewalls are removed, in my case with a cutting torch, there are remnants of the side wall that stand up about 1/4″ from the bottom rail of the container. Even if you could eliminate this remnant, the bottom rail itself is about 1/8″ higher than the surrounding plywood – at least on my containers. There is also the issue of sealing up the gap that exists between the containers.
I couldn’t find any ideas on the web, that I liked at least, on how to deal with this issue. My thoughts ranged from grinding down the metal to routering out a channel in the subfloor – neither of which would be an easy task. I started asking around to my more handy friends and acquaintances, and a builder who was working on my home at the time had the best and simplest idea of all. He told me to use two layers of subfloor with the lower layer away from the bottom rail and wall remnants, and the upper layer spanning that area. I took it one step further by using 1/2″ foam sheathing for the bottom layer to get some additional insulation and possibly sound isolation as well. I found out later that this is similar to methods used to add a subfloor and insulation to basements in cold climates.
Before I installed the subfloor, I covered the gaps with insect screen, 1/4″ hardware cloth, in addition to four metal plates at the ends. The insect screen probably isn’t necessary, and was really just a remnant from some temporary bug proofing while I was working on the cabin. The 1/4″ hardware cloth is required, at least where I live, to keep any mice or rats from chewing their way into the cabin. There will also be 3″ of foam insulation sprayed directly underneath the gaps between each pair of bottom rails. The rest of the container bottoms will only have 1″ of spray foam, although that’s the subject for a later post.
Here’s the 1/2″ foam sheathing on either side of the bottom rails. I did make the gap a bit wider in later rows to reduce a slight rise in the subfloor that occurred over the gap. The screen and hardware cloth probably added enough height in that area to cause the OSB to slope up over the gap. Additional screws in this area can also reduce the tendency of the OSB to rise.
The foam sheathing was then covered with 1/2″ OSB and screwed into the container floors with 2″ coated deck screws. The coated screws are necessary since the plywood floors of the shipping container are treated. The OSB is staggered each row so that any spanning panel overlaps the center of the gap by two feet. 3/4″ tongue and groove plywood or OSB would probably be better, although the 1/2″ seems to be more than adequate when walking around on it. Something that I forgot to use that couldn’t hurt would be panel edge clips (H-clips) between the panels of different rows over the gap.