Shipping Container Housing

SG Blocks of Charleston, NC, refabricates sea-truck shipping containers into modular construction units, and has been getting buzz on the likes of Bob Vila's show, the NBC Nightly News, and other newsy outlets. It's not an original notion, but they seem to have had the most success so far in commercializing it. Or the idea of commercializing it, at any rate. Coverage generally seems to start by showing towering stacks of containers in a port — "up to 300,000 of them stockpiled across the country." Cut to containers being modified, sparks flying from grinders and welders. Cut to a crane setting a modified container onto a concrete-block foundation. Cut to a finished, charming, conventional-looking, stucco-covered bungalow. The pitch is that it's fast, safe (hurricane-proof up to 175 mph, and fire-, mold-, and termite-resistant), affordable, and environmentally friendly. Is it? Dropping pre-framed ~320-square-foot modules in place with a crane is going to move things along at a nice clip at the site; most of the time-eating work has already taken place somewhere else. According to the NBC news piece, "in a day, a crane and a welder can have a container house ready to finish." They're talking about a four-container house: two containers end-to-end on the left, and two more on the right, with an open space in between — the ceiling of that open space to be formed by the bottoms of wooden roof trusses; the gap in the end walls to be framed with metal studs and sheathed with 16-gauge steel. If the only person on the ground is a welder (though the footage of the module placement process shows at least three people scurrying around, in addition to the crane operator), "ready to finish" appears to mean that the day is used to place four container modules, and perhaps do a bit of steel-stud framing and sheathing. Whether modified-shipping-container modules are a faster way to create the bones of a building will depend on design and scope.

The style of small, simple houses shown in the clips can be conventionally framed onsite with surprising speed by experienced professionals. If the offsite work of modifying the containers — which has the upside of avoiding weather delays if the refabrication happens indoors or under cover — is included, it's likely a wash, in both calendar and labor hours. The time and money are invested offsite rather than onsite. (The ins and outs & ups and downs of prefabrication are discussed in the EBN feature, Prefabricating Green: Building Environmentally Friendly Houses Off Site — a good read.) There are safety benefits. Steel framing and sheathing won't burn, it's true. The wood components, such as the roof framing and gable end sheathing, will. Same goes for termites: not much they can do with the steel parts except use it to get to the wood. Metal also isn't a good substrate for mold... but once again there are those wood components, as well as interior finish materials, that need to be considered. In at least one of the projects profiled, fiberglass-faced wallboard was used on the interior because the usual Kraft paper facing is a terrific mold host. With hurricanes, the issues include wind loads and flooding. Catastrophic flooding would have much less structural damage capability and mold potential on steel components than it would for wood framing and sheathing.

And it seems like a no-brainer that the welded steel structure — welded to steel plates embedded in the concrete foundation — and 16-gauge steel sheathing would better suffer wind and wind-borne debris than a wood-stud, wood-sheathed wall built to Southern Florida Building Code standards. (Let me say that again: It seems like a no-brainer. Anybody in hurricane country can feel free to weigh in.) The pitched wood-truss roofs, using what appear to be standard hurricane ties, are nailed to a wooden roof plate that's bolted to the steel modules. Is it a cheap way to build? Bruce Russell of SG Blocks, on Art Fennell Reports, says that their system runs about $20 - $30 a square foot — "for the structural part of the building." Apparently that means the walls. (Math time: a 320-square-foot module at $20 per square foot equals $6,400 per module... installed, presumably. At $30 per square foot, $9600 per 320 square feet. The price of the raw material — surplus containers — is reported to run anywhere between $500 and $2000 each.) He adds, to his credit and with some merit, "You could probably stick-frame in the midwest and do it cheaper than that. But for coastal areas, for expensive areas where it's hard to build — and then [you] expect it to be there for a long time... a 50-year kind of proposition is really what we're about. The affordability comes on both the front side and the back side of the project." Durability is a financial asset — and a green one. As usual, the green part is the most slippery. David Cross of SG Blocks, on Art Fennell Reports, said, "It takes approximately 800 kilowatt-hours of energy to recycle the 8,000 pounds of steel that's in a container. It only takes 400 kilowatt-hours to 'value-cycle' that container into a building block... that's a 95% less carbon footprint." (NBC used the figure 33,000 pounds in their reporting, but that must have been referring to much larger containers.) Two things: 1. Isn't 400 kilowatt-hours 50% of 800 kilowatt-hours? — how does that add up to a 95% reduction in carbon? There's not enough information in that statement — or at their website — to make a critical assessment of the quality of those numbers; and 2. Since these containers are being stockpiled, and not melted down, talking about how much energy it takes to recycle them is a red herring. It would be more useful to compare apples to apples: wall systems to wall systems. The biggest environmental concern that came to my mind was inspired by the hollow, reverberating thud that happened when people in the video clips rapped on the sides of the finished houses. It sounded like... an empty shipping container. The corrugated walls are skinned on the outside with sheet steel, and on the inside with gypsum board — and are otherwise hollow. No insulation is added to the wall cavity. Nor would it help much to do so, with so many thermal bridges linking the two surfaces. Instead, Super Therm 'Insulating Ceramic Coating' is used. The architect for a Florida prototype shown in one of the clips describes the "high tech ceramic insulation" that was "developed by NASA for the shuttle" as having "R-19 for a 50-mil thickness — about the thickness of a credit card." Folks, I don't even want to get into this. A BackPage Primer about "insulating paints" is in the Environmental Building News editorial queue; when it happens, I'll post a link. In the meantime, if there's a LIVE reader who wants to pick up the ball in the comments, have at it. There are any number of ways that proper insulation could be added; all drive up complexity, cost, materials use, and build time. Google "shipping container architecture" for more information... including a Wikipedia entry, an old TreeHugger post, and the Shipping-Container-Architecture Information Repository. Want to do it yourself? Here's a book: Intermodal Shipping Container Small Steel Buildings.