Installing the Subfloor

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.

10 thoughts on “Installing the Subfloor

  1. Pxy

    C’mon Steve, what happens next? 😉

    Very interested in your blog and wondering if I’ll be able to do the labor on my own container cabin. It looks like a lot of work. Would you mind listing the main tools you’re using and if you had any help (other than the welder)? Thanks!

    Reply
    1. Steve Post author

      It’s a lot of work, definitely more than conventional stick built when using more than one container. If you can get by with just a single container, the level of effort/cost goes way down. Unless you have a specific reason (i.e. security) for building a shipping container cabin, you are probably better off with conventional construction.

      The only things I could not do myself were the lifting of the containers, removing the walls, and the spray foam insulation. If someone was really motivated, I’m sure they could remove the walls themselves with a grinder or saw. My cost to hire a welder to cut the walls was so cheap, that I would never have done it myself. In regards to the insulation, I’m already wondering if I should have done something else due to all the problems I am having with my contractor. I will talk much more about that in my next post.

      The things I have hired help for have been the foundation, crane, welding, roof, deck, and spray foam insulation. I tried to work with the people I hired whenever possible to reduce my costs, and make sure it was done correctly. I could have done the roof and deck myself, but it really came down to not having enough time to do it.

      I’m not really using any specialized tools, just the basics. Chop saw, Sawzall, circular saw, jigsaw, cordless drill, Paslode framing nailer, hammers, levels, etc. I still need to get/borrow a table saw when I start on the trim inside.

      Reply
  2. Steve

    I was told by someone who has claimed to have been an expert on these, said in no uncertain terms to remove the original floors. He said the treatment used for the plywood is toxic and will give off toxic fumes.

    Reply
    1. Steve Post author

      He is correct in that virtually all shipping container plywood floors have been treated with toxic chemicals. He is incorrect in that not all treatment chemicals give off toxic fumes. To give off fumes, a chemical needs to have a significant enough vapor pressure to evaporate into the surrounding air. There are several different types of treatment chemicals used in shipping containers today, and we can find out exactly what they used by looking on the container data plate.

      I was fortunate in that my container floors were were treated with Radaleum FHP-60 which has virtually no vapor pressure and therefore virtually no fumes. I could probably have used the floors as is, but I wanted to be extra careful so I encapsulated them with an industrial epoxy. The epoxy coating not only creates a physical barrier from the treatment chemicals, but it also will prevent any significant amount of vapors, if they are even present, from passing through.

      Keep in mind that I did not make this decision lightly, and that I spent a great deal of time investigating it. I am also not unaware of the risks involved as I have a masters degree in Environmental & Public Health and also have considerable industrial experience with hazardous air pollutants – I wasn’t always a computer programmer. The important thing is to consider each container separately and do your own research.

      I encourage you to read my post “The Floor Dilemma” where I discussed this exact issue in much greater detail.

      Reply
  3. Jose

    I noticed that you did the sub-floor AFTER the wall framing. This way you lost the thickness of the bottom framing members that you are going to need to install the drywall. (but probably you found out already).

    Reply
    1. Steve Post author

      Hi Jose:

      I purposely added the subfloor after the framing so that I could remove the subfloor without disturbing the exterior framed walls. I doubt I’ll ever need to do this, but I wasn’t completely sure how my subfloor idea would work out in the end – it’s nice to have a way out in case something goes wrong. If you look at my Electrical Wiring post you will see 2×4’s laid horizontally in the steel stud tracks that provide for drywall attachment on the bottom – this worked out very well.

      Steve

      Reply
  4. Steve Burdsal

    Can I get a Little more detail on the subfloor at the seam of containers.
    I may have missed in my read. How did you get the floor at the seam level ?

    Reply
    1. Steve Post author

      Steve:

      I think the first picture in my post shows it best. Since the wall remnants stick up a bit, I needed to create an open space under the subfloor to accommodate them. The 1/2 foam layer was not applied near the seams, so when the OSB was applied over the foam it floated above the wall remnants.

      Now there were some final adjustments to be made since there were some small differences between the floor heights along the seam. This was easily accomplished by the screws I used to attach the OSB to the container flooring. Since the foam was compressible, I could adjust the tension on the screws to raise or lower sections of each panel to help them line up with the others.

      Hope this answers your question.

      Steve

      Reply
  5. Paul Stanley

    I was wondering, you mentioned it would be possible to pour a cement floor. What are your thoughts on radiant floor heating? Once the tubing, manifold and boiler (which can also supply domestic hot water) are installed it is relatively inexpensive to operate. I have it two traditional built buildings on my property. I skimmed through a lot of the blog, but didn’t see how you heated yours. Radiant heating doesn’t require any fans or duct work, thus saving space.

    Reply
    1. Steve Post author

      Paul:

      I think radiant floor heating is outstanding – for a permanently occupied home. The problem with a cabin such as mine is that it’s unoccupied for weeks at a time during the dead of winter. Radiant floor heating is just not optimal for an off grid cabin.

      What does work for me though is a wood stove. Reasonable initial cost, easy installation, no fans or duct work, and fuel is cheap, or even free, where I am.

      Steve

      Reply

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