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Last week, our focus was rain screens and how they help house exteriors become more durable. This week, we're going on site for the installation of a green or "living" roof.

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What is a Green Roof?

Instead of metal or shingles, what if your roof had plants that covered some or all of the surface? That's the big idea of a green roof. Vegetation is planted on the roof that serves to protect the home from heat and weather, reduce fire risk, use rain water responsibly, increase biodiversity, and more.

This style of roof has ancient origins and today new technology is making it more effective. But it's not that easy. A roof, green or not, still has to be well-supported and prevent water from entering the home. When you add layers of moisture protection, soil, and plants, it can get complicated quickly.

Green Roof Design

Build Livable contributors Jon and Mari invited me to be a part of their green roof installation and I couldn't resist. Their two-story home is on a steep slope that is often visited by hungry deer.

Being a serious gardener, Mari saw the roof as a perfect place to have a garden and entertaining area. The idea of a green roof was born during the project, which offered a complication: the roof was not initially designed to hold the weight of a green roof. The team came together, along with green roof consultants, to find a way to make it work.

They chose to use a semi-intensive green roof design, which helped them reduce the weight of the roof system. This design is great for mosses, grasses, sedums, herbs, and flowering plants.

The layers of the roof are below as designed by Columbia Green. The construction team was very careful to seal the roof with multiple layers of waterproof membrane before the green roof was added.

The Installation

When I arrived, most layers had been installed. I was there to see it completed. This is the filtration layer.

The roof is designed with a slight slope from the middle to the north and south edges. This way, moisture can drain to gutters and down to the ground. Water drains through the rock-filled channel (below) before reaching the gutters, which prevents the soil from being washed away. To prevent the drainage holes at the edge from becoming clogged with debris, a perforated pipe covered with drainage fabric was placed below the rocks along the channel.

One of the biggest challenges is getting thousands of pounds of planting material and plants to the roof. Jon and Mari are fortunate to have a GC (Drew Reed of CA Reed Construction) who was a crane operator at the time.

Drew and the crane got to work delivering soil (planting medium) to the roof, six cubic yards at a time.

The bags had a pull-string at the bottom that made pouring easy. The person handling the bags had to be in constant contact with the crane operator so the soil could be distributed evenly.

Once the soil was down, it was a team effort to spread it out, from 8"-12" deep. It could be deeper (heavier) in some places where the roof had extra support.

Next the crane delivered sedum tiles, which make up the bulk of the surface on this green roof.

Among the sedums below is Angelina, which is evergreen and drought tolerant. These succulents store water in their leaves and grow with limited maintenance.

Once two pallets of the tiles were delivered, the team laid them out, along with stepping stones, to complete the project.

With the sedums down and watered, the roof could begin its life, literally. The sedums make up the bulk of the roof's surface, but Mari will plant more over time. I love considering the view from above and how the green roof creates an illusion of undisturbed nature.

Did you find this helpful? Do you have ideas for future issues? I would love to hear from you. Reply to this message or email me anytime at lee@buildlivable.com.

Lee LeFever, Build Livable​

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