container floor construction

My last post on container wall construction seemed to be very popular.  Thanks to everyone who clicked, read and offered comments.  I hope everyone enjoys this post on how to construct the floor of a shipping container.

First a little review:  As you’ll remember from last time, containers are not initially intended to house humans….or dogs, cats…really anything with skin and/or fur is not meant to be housed in these things.  The paint is toxic and needs to be either sandblasted and coated with impervious paint, or (if you take the short cut) simply painted with impervious paint (this is really not recommended).  The floor, also, is not friendly to us or anything else as it is typically either OSB or standard plywood soaked in formaldehyde so that it doesn’t rot as it travels across the globe being beaten to hell by God and Creation.  So, we need to get rid of it, again, safely.  Contact your local EPA to find out how to properly dispose of this crap – believe me you don’t want to hang on to it.

Once you’ve removed the plywood floor, you’ll see the structural steel ribs below that give the container it’s horizontal support.  Now, we’ve got a couple of options on how we can build our floor.  It all depends on your foundation type: whether your containers are off grade on a stem wall or sitting on a slab.

The easy option is to screw down a new subfloor (either plywood or OSB) and, while you’re spraying the exterior of the container with SPF, simply spray the underside of the floor as well, thus insulating and sealing the underside of the container.  Then install whatever floor finish you choose – tile, vct, carpet, hardwood, engineered wood, cork, bamboo…you could even leave the plywood exposed and finish it with a polyurethane for that “industrial” look.

Another option for the floors, one that is much more sturdy and permanent, in my opinion, is to use concrete.  A typical concrete floor with deck is approximately 4″ thick (2 1/2″ of corrugated metal deck and 1 1/2″ of lightweight concrete fill).  If poured on grade, you’ll also have about 2″ of foam insulation underneath with a vapor barrier to prevent  water intrusion through the slab.  For a container, what we do is first lay in exterior grade plywood (5/8″ min.) between all of those steel joists, followed by 2″ of rigid foam insulation (you can find this stuff everywhere – even for free).  On top of the foam you pour your concrete (3″ – 4″) with a medium gauge welded wire fabric.  The concrete is leveled, smoothed and finished in any number of ways – saw cut, stained, brushed, etc.  Also, don’t forget to add in at least 2 expansion joints across the length of the container.  Steel and concrete move in very different ways and the last thing you want is a huge crack from expansion and contraction of the steel.  Essentially what we’ve created is a reinforced waffle slab that is insulated between the steel joists.  Any thermal bridging at the joists will be minimal.

Whichever option you choose for the floor of your new container home, be sure to consult with a local structural engineer and your local building inspector/plans examiner to make sure that you are building to proper code.  While containers provide an inexpensive building unit with which to construct a home, remember there are important steps that need to be taken in order to make them habitable and safe according to modern building codes.

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