Container houses fixed structure roofs may serve different purposes. Roofs of cargo shipping containers are designed to meet the well-defined requirements of the transport industry. No wonder that in new, not originally targeted applications like housing, container flat roofs are often far from a perfect solution.
The most popular roof designs in the traditional residential industry include:
It’s a roof with 4 – (usually gently) sloping sides. If built on a square plan, it looks like a flattened pyramid. Due to the lack of vertical sides, they have very good wind resistance.
It’s the most common shape of the roof mostly appreciated for a “free” attic area that can be used as an extra habitable space or storage.
It’s a 1-slope, a quite undemanding roof (as its name suggests, often used for sheds, and cabins…).
It’s part of the original container’s design, but due to a different set of requirements, it may need substantial re-design to meet new goals.
All of them have some pros (including not mentioned here architectural values) and cons, but in general, they are not optimal for container-based houses (especially off-grid ones). It’s because they have to address a significantly larger set of requirements than just the attic space and wind resistance. Of importance will be for example maximum load, ability to collect rainwater, space for solar panels, ventilation assistance but also the ability to be used as a garden (green roof) or an above-the-ground deck.
These are the most popular solutions for small container houses (one to a few modules). In the case of a single 20 or 40ft module shed roof can be a perfect solution for solar panels as well as for harvesting of the rainwater. For two adjacent containers, the shed roof provides an effective umbrella over an otherwise exposed gap along the walls. Note that corrugated roofs of cargo shipping containers are designed to channel rainwater towards their long side edges (shortest distance to the ground). However, this mechanism will not work properly when two (or more) containers are set side-by-side. Partially, the water will either flow to the gap between containers’ walls (if the gap is left unprotected) or collect stagnant along the join. In the long term, both scenarios are catastrophic!
Like everything in earthly life – shed roofs have their limits. It seems that covering 3 or more adjacent containers with 1-slope roofs is rather impractical. However, the good news is that kits of Modular Roof Systems specially designed for 20ft and 40ft shipping containers are already available on the market. That means, it can be an easy and painless DIY job!
also found their way into cargotecture, although in a specific configuration known as a “Bridge-Roof” designed to cover the space between two separated rows of containers. It’s a great architectural solution offering a large, protected open living space, especially precious given the limited width of container modules.
Bridge Roof concepts. Source: Container Construction Systems.
Farmhouse – Practical implementation of the Bridge Roof. Source: BackCountry Containers
The covered area can be left open and used as a garage or outdoor living space or partially integrated with side containers and partially used as a porch like the above farmhouse. However, the most attractive solution is a fully enclosed, weather-protected space integrated in the envelope of the house (residence). An example of such cargotectural design is the luxurious 4,000 sq. ft 12-Container House (Maine, USA) designed by architect Adam Kalkin. The floor-to-ceiling glass walls offer protection from weather elements, but at the same time offer an incredible opening to the outdoors. In fact, that’s one of the main goals of cargo-mania: low eco-footprint integration with nature. While luxury (as with every excessiveness) may not go well with eco-friendliness, it is certainly the trend in the good direction.
12-Container House. Note the incredibly large living space so much in touch with the surrounding nature. Source: Design Boom (USA), Photos: Peter Aaron
Now it may be clear that Cargotecture does not have limits, and while the popular saying that the sky is the limit may still hold, more realistically sounds the statement that the real limit is human imagination!
Flat roofs clearly dominate the apartment building industry, but despite their low initial cost, they are rarely seen on residential houses. They are rather architecturally unattractive and require maintenance, especially in wet (rain) or colder (snow) climate zones. For the same reason, they are rarely used in Cargotecture. Below, is a rare example of a “quasi-flat” roof protecting a container from the weight of accumulated snow. It’s architectural composition, in combination with glass adds a strong accent of elegance and modernity and that was probably a driving force for this design. Anyhow, it’s a beautiful mixture of ruggedness, glass, and light with Mother Nature at her best.
Let’s start with physics: metal is a good heat conductor. When shiny (which is not the case with raw Corten steel), it can partially reflect sunrays (with efficiency depending on their angle of impact). The truth is however that a flat metal roof (and with it, the whole container’s metal structure) exposed to the scorching sun will quickly transform into an oven!
An extra roof-over-roof with an air barrier in between can provide the first line of defense against the heat. It will slow the transfer of heat to the metal’s structure and overhangs (if any) will provide shade for the walls and windows. Additionally, if properly designed (shaped), the extra roof can take advantage of physics by creating low-pressure zone(s) above the container house generating this way a natural cross-ventilation process (See: Containers Ventilation)
The air flowing under the roof evacuates accumulated hot air helping to keep the interior cooler.
In windy (breezy) areas air flowing under the shed-type roof will increase its speed when passing under the lower end of the roof. This will create a zone of lower pressure (pure physics) sucking potentially hot air accumulated in the house. Such roofs are part of energy-neutral designs – they enhance the natural phenomena and then take advantage of them.
But from the architectural point of view, the roof-over-over-roof also represents a “statement” adding character to otherwise very regular geometrical shapes of shipping containers.
Most manufacturers of custom roofs use metal sheets made from durable, corrosion-resistant, low-maintenance metals sheets like hot-dip galvanized steel, Aluzinc steel (coated with a compound of Aluminum, Zinc, and Silicon, Colorbond (Australian brand of ZincAlum based anti-corrosion steel). Typically, they are available in a vast selection of colors.
Container houses fixed structure roofs as part of the water harvesting system
In some cases, rainwater collection may be just part of our eco-consciousness (if used for gardening or watering grass, it does not need any extra treatment). However, in off-grid locations most likely every drop of falling from the sky water is a gift not to pass on. Obviously, the most effective way to harvest rainwater is to channel runoff water from the roof to a storage tank. While it is possible to accomplish even from flat roofs, pitched custom-built roofs will make it more effective and easier (especially when the house is built as a multi-modular structure). Note that in contrast to pitched roofs, flat ones will have a tendency to accumulate more debris, leaves, dust, etc. And even if the water is intended only for outdoor use (gardening), the storage tank will need more frequent maintenance service!
Although it is out of the scope of this article, please note that simple “First-Flush” systems can divert the initial dirty water carrying dust, leaves, birds’ droppings, dead insects, contaminants, etc…. out of the main water storage system!