I suppose we might want to start off this post asking the question “what is a green roof?” Is it a roof that is painted green? It could be, but not as it applies to our discussion. When we say “green roof” what we are really referring to is a roof that has greenery on it, i.e. planting soil and grass of some variety. This isn’t exactly a “new” technology either. Man has been “roofing” with natural materials for centuries. But obviously we’re stuck in this whole “the world is going to explode tomorrow unless we build everything sustainable and green” mentality that it’s become a “hot topic” and hits all the right political pressure points. But before we get in to the “nitty gritty” of green roofing, let’s first discuss some benefits of using this technology.
First, it aids in reducing the heat island effect that buildings, especially in urban areas, are prone to create, which is what happens when you have a material that absorbs and stores the suns’ energy during the day and releases it at night rising the local ambient temperature above normal levels.
Second, a green roof acts as a natural insulator to reduce your need for hvac (heating ventilating and air conditioning). Have you ever dug a big hole and felt the ground with your hand a few feet down? It’s much cooler to the touch because the soil above it keeps it insulated. It’s like living in perpetual shade.
Lastly, it just looks really cool….really. 🙂
So, what makes up a green roof? What are the typical components and how do we adapt this for basic container design? First you have to have a suitable load bearing structure to place your growing medium onto. This can be many things – timber framing, steel joists, reinforced concrete, or any other typical roof framing methods. Next you need a suitable waterproof membrane to keep moisture away from your structural supports. Then there is a air and water drainage layer. Why is this important? Air needs to breath and circulate water just like we do. If the soil doesn’t get any air movement, or if there isn’t a way for water to move in and out of the soil, it can rot and break down and eventually become unsuitable for growth. This would be bad.
Now, on top of this air and water drainage layer we can put our top soil. What type of topsoil you use will depend on what you are attempting to grow. This can be almost anything, within reason – typical grasses, or small shrub plants, or even succulents. In order to minimize the need for watering and maintenance you’ll want to plant something that is indigenous to your specific geographic location.
Once you’ve added your top soil, obviously it’s time to plant. Just like any lawn, you can either plant from seed or use plugs or lay sod. It’s up to you and your budget/time schedule. Below are some eye candy examples of green roofs used all over the world in different climates.
Implementing a green roof atop a shipping container is really no different. I’ve talked often about a shipping container being cost effective because you’re purchasing your structural envelope already assembled. This isn’t quite true when talking about a green roof. Unfortunately the roof structure of a shipping container is not quite strong enough to support the layers of membrane, drainage, dirt and greenery that we need without buckling. So we need to reinforce it. The easiest way to do this is with reinforced concrete. This way we can create either a flat or sloped surface much thinner than with lumber and sheathing or steel and decking. Once we have our roof structure, we simply layer on the items mentioned above and WHAM-O : green roof on a container. 🙂
In the image above you can see that the green roof is built up atop the container. It has it’s own structure separate from the container.
Bottom line, green roofs are efficient insulators, aesthetically pleasing and environmentally sustainable if done properly. So, for your next container project, think about employing a green roof. You’ll get a more efficient roof insulation as well as opportunity for additional flexible space for your home.
If you simply choose a lightweight material and a vine like plant that would be grown from the ground to the top of the container, would it have the same effect ?
To a very small degree yes. The real benefits of a green roof are in the thermal mass properties – the ability to store up heat energy during the day and release it at night without affecting the interior temperatures. A green screen, like you describe, will reflect some heat energy and provide a small air space for passive ventilation of the surface metal, but not enough for realistic purposes.
Thanks for the comments and for visiting the site! Cheers.
Thanks. My container is near the sea on a small island in the indian ocean. I opted to put pumice stone on the container roof with a few pots in which I planted native plants known for their extensive growth with little ressources. Don’t know how it will turn out but I’ll keep you posted.
that is certainly an economical option and a preferred one. Anytime you are implementing a green roof you want to use indigenous flora and fauna for a specific region. It allows for minimal irrigation and typically very low maintenance.
I’d love to see some photos of your container.
How do you cost something like a green roof on a shipping container? Given the low cost of the container and the need to reinforce the roof with concrete, how much does the price increase?
The green roof would need it’s own structural support actually. The cost of a green roof is typically offset by its benefits for the home itself. But I would say you’re looking at $5-10 per square foot of roof for materials.
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