How to Install a Green Roof: Step-by-Step Guide

How to Install a Green Roof: Step-by-Step Guide

Green roofs, also known as living roofs, are an innovative way to transform your rooftop into a vibrant, eco-friendly space. Not only do they enhance the aesthetic appeal of your home, but they also provide numerous environmental benefits, such as improved insulation, reduced urban heat island effect, and increased biodiversity. In this comprehensive guide, we will walk you through the entire process of installing a green roof, from initial planning to final maintenance.

Prep the Roof

Before you begin the installation process, it is crucial to prepare your roof properly. Even a flat roof should have some pitch to ensure water drains toward gutters. For a green roof installation, the pitch should be at least ¼ inch per foot of run. This helps prevent water from pooling and ensures that the roof remains dry and healthy.

• Structural Assessment: Consult a structural engineer to determine if your roof can support the weight of the green roof system. When saturated, each tray in a modular system can add up to 30 pounds of load per square foot, which is significantly more than a traditional roof built to support about 25 pounds.
• Waterproofing: Apply a high-quality waterproof membrane to the roof deck to protect the building from water damage. This is the first and most critical step in green roof installation.
• Root Barrier: Install a root barrier to prevent plant roots from penetrating the waterproofing layer. This barrier is typically made of a durable, chemical-resistant material that can withstand root pressure.

Choose the Right System

There are several types of green roof systems available, including modular trays and built-in-place systems. Modular trays, such as the LiveRoof system, are popular for residential applications due to their ease of installation and maintenance.

• Modular Trays: These trays are filled with a soilless engineered growing medium and fully mature sedum plants. They are heavy (about 40 pounds each) and are typically installed by certified contractors.
• Built-in-Place Systems: These systems involve laying down a drainage layer, a separation profile, and a growing medium, followed by the installation of vegetation mats or plugs.

Install the Green Roof

The installation process for a green roof involves several key steps. Here is a detailed guide to help you through each stage:

Step 1: Clean the Roof

Start by cleaning the roof and removing any dirt, waste, or other materials. Check that the roof covering is not damaged to ensure that the roof is waterproof.

Step 2: Apply Root Barrier Foil (Optional)

If the roofing is not root-resistant, it is necessary to use a root barrier foil. Cover the roof edges and ensure that the foil joins well with an overlap of 50 cm.

Step 3: Apply Protective Cover (Optional)

Roll out the protective cover up to the roof edge and cut to size. Ensure that the protective cover joins well with a small overlap.

Step 4: Apply Drainage Layer

Roll out the drainage sheets to the roof edge, perpendicularly over the root barrier foil. If necessary, prepare the cutting of the drainage to size on the ground or take measures to cut safely. Never cut directly on the roofing.

Step 5: Apply Separation Profile

Cut a piece out of the root barrier foil, protective cover, and drainage layer at the rainwater downpipe(s). Cover the downpipe with a wire balloon guard, leaf trap, or inspection pit. Place the separation profile at least 20 to 30 cm from the roof edge, with the base on the side of the gravel strip.

Step 6: Apply Roof Garden Substrate

Spread the roof garden substrate evenly with a rake. Prevent the substrate from getting between the drainage tracks. Measure if the substrate is the correct height as indicated in your system structure. Completely saturate the substrate layer with water before installing the vegetation mats.

Step 7: Apply Gravel

Apply the gravel between the separation profile and the roof edge. Bring the gravel layer to the same level as the separation profile.

Step 8: Apply Vegetation Blankets

Roll out the vegetation blankets over the substrate layer. Start with the end of the vegetation blanket on top. Carefully roll the end of the blanket back and make sure it is in the correct position at the start of the track. If necessary, cut or saw the blanket to the right length. Use a sturdy serrated knife or saw. Ensure that the vegetation blankets join well without overlap. Any bare patches can be filled with residual pieces of the vegetation blanket.

Connect the Trays

With a modular system, any tray can be removed from the roof for maintenance without disturbing the others. In this system, plastic lips on the front and right sides overlap the left and back sides of neighboring trays for stability, creating a blanket that eliminates seams and reduces temperature fluctuations. Feet built into the underside of the trays keep them elevated ½ inch above the roof’s surface so that runoff can easily flow underneath toward the gutters.

Cut Trays to Fit

Usually, trays have to be cut to fit between the last full tray in a row and the edging. An installer measures for each end piece, then transfers the mark to a full tray with a wax pencil. Because the trays are filled with a growing medium made of tough aggregate, a gas-powered concrete saw fitted with a masonry blade is used to cut the trays. The cut end butts against the last full tray in the row. On this job, one installer laid the rows of trays, another took measurements for the end pieces, and a third made cuts on the ground before sending a few rows’ worth of end pieces up to the roof.

Water Well

Once the trays are installed, they are watered to settle the soil. Green roof plants like sedums usually don’t require irrigation unless there’s a four-week spell of high heat with less than 1 inch of rainfall. During dry spells, the growing medium can shrink, leaving it vulnerable to weeds. You can irrigate this roof with a self-coiling garden hose threaded into the second-floor bathroom sink faucet. A yearly haircut and occasional fertilizer as indicated by a soil test are all that’s needed to keep the green roof fit and trim.

Pro Tips and Best Practices

• Structural Engineer: Always consult a structural engineer to ensure your roof can support the weight of the green roof system.
• Waterproofing: Use a high-quality waterproof membrane and root barrier to protect your roof from water damage and root penetration.
• Drainage: Ensure proper drainage by installing a drainage layer and separation profile.
• Vegetation: Choose plants that are suitable for your climate and can handle both deluge and drought conditions.
• Maintenance: Regularly inspect and maintain your green roof to ensure it remains healthy and functional.

FAQs

Q: Can I install a green roof on a flat roof?

A: Yes, you can install a green roof on a flat roof, but it should have a slight pitch (at least ¼ inch per foot of run) to ensure proper drainage.

Q: How much weight does a green roof add to my roof?

A: When saturated, each tray in a modular system can add up to 30 pounds of load per square foot. Consult a structural engineer to ensure your roof can support this weight.

Q: What type of plants are best for a green roof?

A: Sedum plants are commonly used for green roofs because they are hardy and can handle both deluge and drought conditions. Other suitable plants include grasses, herbs, and wildflowers.

Q: How often do I need to water a green roof?

A: Green roof plants like sedums usually don’t require irrigation unless there’s a four-week spell of high heat with less than 1 inch of rainfall. During dry spells, water the roof as needed.

Q: How do I maintain a green roof?

A: Regularly inspect the roof for any signs of damage or weed growth. A yearly haircut and occasional fertilizer as indicated by a soil test are all that’s needed to keep the green roof fit and trim.

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