How to choose and install a green roof

Green roofs add so much more than just an aesthetic effect to homes. Living roofs are eco-friendly in many ways, such as by managing storm water runoff, providing insulation and reducing the heat-island effect. Even better, small-scale green roofs are not very complicated to make and can easily be turned into a DIY project.

Which green roof to choose

Small-scale green roofs are perfect for placing under the main roof—think of the porch roof or garage roof, or the top of a shed. First, you need to choose whether your green roof will be extensive or intensive. An extensive green roof needs less maintenance, while an intensive roof with more layers requires more maintenance. The area where you want to install the green roof will help you decide, due to whether frequent maintenance would be possible or convenient.

It is best to get advice from a specialist if you have a roof that slopes over 10 degrees or under 2 degrees, as there might be further design strategies to take into account. Also, only roofs that are in good condition, without damage or leaks, should be considered for installing a green roof. The weight of a small green roof can be between 13 and 30 pounds per square foot before saturation, and whether the roof can hold the extra weight should be calculated as well.

Vegetated roofs consist of a few different layers. Whether the green roof is on a small home or a skyscraper, these layers are more or less the same:

Waterproof layer

All green roofs need an additional layer of waterproof material that is root-resistant. A single sheet, such as heavy-duty pond liner from a local store, is perfect for this layer. When applying, mark the outlets so that the area can be cut open in a later step.

Drainage layer

Drainage is essential for excess water to escape from the roof. Make sure the outlets are cut into the containment frame, which will allow water to flow into the gutter of the roof. It is crucial that the outlets stay clear at all times. By using pebbles around the outlet point, you can avoid vegetation establishing itself in the drainage system or around the edge of the roof.

You can also lay out moisture blanket or geotextile membranes (which are fungi- and bacteria-resistant) to help the plants keep water. Alternatively, a gravel or limestone chip layer can be spread on top of the waterproof layer to ensure drainage.

Substrate layer

The soil needed for a green roof should have a ratio of 70 percent inorganic material and 30 percent organic material. Low nutrients and lightweight substrates are perfect for a green roof.

Vegetation layer

The last layer is the vegetation itself. The types of plants that you will have will depend on the type of green roof you are installing (extensive or intensive). Seed mixtures can be bought specifically for green roofs. Green roof blankets can be rolled out, or plants can be directly planted into the soil. Whichever method you choose, keep in mind that you can tailor the planting to attract certain species of plants and wildlife.

Last, check the condition of your green roof at least a couple of times a year, and keep it chemical-free. Your home will soon be looking more attractive, even as you contribute to a healthier environment.

Learn more about living roofs

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