Shipping container houses are gaining popularity globally and are seductively attractive with their modern looking lines, colours and shape. Like many great ideas, the re-use of containers for housing makes complete sense on the surface, but may not be the best use of materials when you look at the big picture. While it may work fine in a moderate climate, slugging it out through a Canadian winter in a metal box may not be the wisest of moves.
Five reasons why we aren't sold on this noble attempt at alternative housing:
1. Energy efficiency:
Metal is a conductor - of both heat and cold - as evidenced by the popularity of metal frying pans over say...wooden ones, for example. This makes metal a less than ideal substance in many applications of home construction.
To render a container house energy efficient in a cold climate, you'd need to insulate it outside, and possibly inside as well. You would need to ensure on all sides, including the bottom, that the metal does not act as a thermal bridge, robbing you of your hard earned heat.
In order to attain a modicum of energy efficiency, you would end up still having to build an entire additional structure to accommodate insulation, as well as install exterior cladding. So gone is that nice modern metallic look you were after as well as the very reason for doing this, having the metal container act as the main structural wall.
Optionally you could put all your insulation on the interior, but to have a sufficient amount of it you would significantly reduce the amount of usable interior space.
It would be easy to think that stacking containers would improve their efficiency, but this is not the case as there is no exterior building envelope. Given that metal would pass continuously from the exterior through interior division walls, it would still be necessary to insulate all four sides of the container or risk significant heat loss through thermal bridging.
This would add significant material use and cost compared to a building constructed without highly conductive materials extending into interior division walls.
Metal is infinitely recyclable, so the container has not been 'saved from a landfill'. Put a chunk of metal at the end of your driveway and it will disappear, destined for a metal recycling depot where someone will be handed some cash in exchange for it. The monetary value alone of an old container ensures it will be recycled one way or another.
Metal is highly polluting and energy-intensive to extract and manufacture, so once we have it we are best to put it to good use. When used to form a structure, the ecological footprint and embodied energy of metal is far worse than that of wood.
From a green building material standpoint, materials should be used in their most sensible manner, meaning it would be better if metal were kept in circulation and applied to a use that only metal can fill.
A metal container house is strong, but so is a solid wood-framed house. There is a common association between container houses and green roofs, partly due to the fact that containers can withstand heavy loads. They certainly can, but this line of thinking underestimates the properties and strength of wood. You can easily frame a wooden roof to carry the added weight of soil on a green roof, and wood is renewable, usually local, and more sustainably harvested than metal.
Container houses may subject you to toxic substances, as it is hard to know what was previously contained in a container before you moved in. Pesticides, chemicals or other toxic materials may have left some residue behind, despite the best cleaning you can give it.
A container house doesn’t automatically mean a cheap build. For reasons mentioned above (framing and insulation), and because the technical issues are rather complex (drilling holes, managing junctions, electrical connections, etc.), the conversion of a container to a house can actually end up being more expensive than if you left the container out of it altogether.
With the need to build another entire structure on either the inside or outside of the container, the metal itself is reduced to being little more than an interior finished surface, or acting as the air / vapour barrier, where it isn't necessarily doing that great a job anyway. Using old containers as the launching pad of a home building project locks up huge amounts of metal that could be far more useful in other applications.
With all that said, kudos to container house builders for their vision, innovation, compact design and re-purposing of materials. It's just that in our opinion, this is a housing solution better suited to climates that are a bit more forgiving than here in Canada. Ironically, given the common intentions of their advocates and builders, a container house will by square foot of living space end up using more raw materials and cost more to operate than a conventional wood-framed house.