Green roofs are great! They offer a great element of style to any structure and are completely practical as a way for a property owner to help the environment in their own small way.
A green roof will also save you money! It will insulate your house and roofing material for the life of the building.
Let me show you how to build a green roof with pictures!
There are two types of green roofs
Extensive – Think simple. Less soil and small plants that only grow as high as grass. Grass being a very common extensive roof. This system is much lighter so you roof structure doesn’t need to be as strong. Its also low maintenance which is nice if there isn’t any easy access. But there is no reason it cant look cool too.
A few examples…
Intensive – This would be more of what you think of when using the term “rooftop garden.” This system is designed around any size plants you wish to plant. The structure of the building is specifically designed to hold the additional weight. Its much more expensive to build and will require maintenance such as pruning of the plants.
A few examples…
My only experience is building an intensive green roof on a home in Los Angeles. Here is how I did it…
The first picture below is the rough framing. Because we are building an intensive green roof or a true rooftop garden there will be a large amount of weight for the structure to support. Here we are opening up the roof to expose the framing and we will be installing engineered wood beams and blocking per the engineers details on the construction plans.
This next picture is after we have closed up all of our framing (we were remodeling more of the house as well). The curved wall is the separation between people and plants. Its hard to notice but look carefully at the back corner in the picture below. See how the wood has a slight incline? That’s the slope for water to drain outwards. In the framing stage we focus on creating our space with any walls or boundaries, making sure our garden floor has proper slope and drainage points and also access points for any electrical or irrigation.
Notice the pieces of metal in the picture above. The roofers are just starting to prepare to waterproof.
Here is a picture looking through a drainage point. I did not use this piece of plastic is was merely a place marker for something else later. Notice how the wood slopes toward our picture? In this green roof design water flowed out of the garden and under an elevated deck where it combined with any water that was flowing off from the deck and the both exit to the side of the building.
Notice this piece of metal in the bottom of the picture? This is what I replace the plastic pipe with in the above picture. These are custom made galvanized metal flashing. These drainage points are often called scuppers.
In the two pictures below you can see the first layer of waterproofing material. This is a special type of coating for second story decks and is very common in construction. Your state may have a different brand but the three basic elements are metal flashing, plastic netting and a roofing cement.
(This next picture is another area on the project but it really shows all three elements)
Now, not to disappoint you but, I had a lot of irons in the fire when I was taking these pics and missed a few steps. However the picture below shows the majority of them. Let me be thorough and explain exactly what we did after the roofing cement.
1) We layered everything with a product called bituthane. Its a thick rubber sheet material that is sticky on one side. After the roofing cement is dried we applied a layer of this bituthane over the entire surface.
2) Next we installed a layer of thin foam panels which are designed for gardens within a building. It protects the insulation from sharp objects. In the picture below you can see these as the green color. This green foam panels are fairly thin, maybe 1/4″, and are sold for this purpose. Don’t use foam from a craft store. The foam we used is green guard pb4.
After the foam the waterproofing is considered done. So we start building our actual garden.
Being the journalistic dilettante I am…we will rely on this graphic to compensate for the picture I didn’t take. I consider this graphic to be semi-accurate but its the best I could find.
Do you see the green foam in diagram below? Yes that’s the green foam in my picture above.
1) Now above the green foam is a root barrier fabric. This fabric essentially contains the plants so that the roots cannot spread into the roofing our houses structure. I’m sure you have seen a piece of concrete sidewalk lifted by a tree root. This fabric prevent roots from making tiny passages into the water proofing material below. Make sure and add at least three layers to be safe and make sure there is a 6″ overlap on each joint.
2) When installing the root barrier fabric consider you drainage points. Remember my picture above of the plastic pipe as a place marker? Well at each of these points my root barrier fabric did not have a support from the wood wall. It may look fine during installation but over time the fabric will push through this space like toothpaste being squeezed from a tube. You need to install a plastic grid to support your root barrier at any drainage point.
3) I actually add a layer of expanded clay above my protection fabric. This gives me a nice flat surface to begin building the garden and also add another layer of protection for my roof. I use expanded clay because its light and cheap.
4) Now you can add a drainage layer. This is essentially a layer of tiny plastic cups called dimple board. These are sold on the internet for use in putting greens. The sheet of miniature cups basically have holes over all the high points at the cups rim but contain water inside the little cups. This allows excess water to flow over the top of the cups and out into the drainage while retaining a small reserve of water inside the cups themselves.
5) The graphic below shows a filter layer but I did not include this step. I chose to begin adding dirt, soil or compost.
In the below picture you can see the garden is basically done and we are installing the elevated deck system. Notice by the left leg of the worker that there is a pipe and low voltage wire running under our deck which would power our irrigation and lighting. Also notice on the right that our green panels and root barriers are haphazardly taped onto the wall. Eventually we installed some plastic fuax wood deck board over this area to give it a nice finished look.
Here is the finished product. We turned this roof into a garden complete with a complete kitchen including BBQ, Stove Top, Sink, refrigerator, cutting board, airtight food storage and a wood fire pizza oven.
A view from the street at our new roof!
Hopefully this will help you get a better understanding if how you can build your own green roof. A few important points I cannot stress enough for those do-it yourself types out there.
I suggest hiring an engineer to examine the structural loads. Remember soil holds water and water is heavy!
I also suggest hiring a waterproofing company for the waterproofing. Don’t take the risk of finding a leak a year later and having to tear everything out.