green roof installation

Green roofs are alternatives to traditional roofing. Basically they are a rooftop garden, mainly conceived to cool buildings and to reduce air conditioning costs.

A complex task

Installing a rooftop garden is a complex task. You should consult a landscape architect when selecting the plants, or an engineer or structural architect to analyze the capacity of the roof to support the weight of the green roof.

There are several very important questions you should take into accounted, associated with the several green roof layers.

Pay attention to the types of plants, or to issues like soil, irrigation and drainage layer, root barrier or waterproof membrane layer.

Types of Roof Top Gardens

The most common green roofs in the housing sector is the so-called extensive green roofs. They involve a small amount of soil depth (2 to 5 inches) and low ground covers vegetation and grasses; they do not demand large weights, and the demanding maintenance is limited to the first months.

But there larger and more ambitious types of green roofs, involving larger amounts of soil depth (one foot minimum), large shrubs and trees, and regular maintenance requirements and complex drainage and irrigation systems. This type of green roofs is characteristic of large buildings, and is commonly called intensive green roofs.

green roof layers

A green roof involves several layers:

-vegetation;
-soil;
-a filter and a waterproofing membrane;
-a root barrier;
-a drainage and irrigation system...
-a roof membrane...

And, sometimes... also an insulation layer.

Selecting the plants for a green roof

Pay attention to the plants used in a green roof. They should be noninvasive and native plants. And they should be drought-resistant and wind-resistant. Look for the advice of an expert on this critical issue.

During the first months (or even years) the plants may demand special maintenance, and the access to them should be previewed.

As expected, the type of plants demands an adequate soil type and depth. When selecting the type of plants and the several layers of a green roof, take into account the slope of the roof (green roofs demand flat roofs or low sloped roofs), the irrigation system, the wind prevalence or the strength of the roof beams.

The soil type and mixture

The soil type and mixture, or its depth, depends on the type of plants. 2 to 5 inches of soil is common, but there are rooftop gardens that demand much more, namely if they involve shrubs or tall plants and trees.

To prevent the wind from blowing the soil of a green roof, technicians apply a wind erosion layer: a thin blanket, placed on the top of the soil dirt. Burlap and jute blankets are common (the blankets are usually made of materials that will dissolve after the plants take root).

Irrigation and drainage layer

An irrigation-drainage system is critical in a green roof installing. The water shouldn’t be allowed to sit on the roof membrane. And that is prevented through a drainage layer, commonly supported by a filter or an egg-crate fabric, installed to driven the water to a drain.

Jute and burlap layers are also used to filter the water.

Root barriers

Some plant roots are extremely aggressive and can penetrate the roof membrane. To prevent it, the green roof should have a well-installed root barrier, commonly made of foil or some adequate plastic material. Root barriers are critical elements on any green roof. An incorrectly installed root barrier will be a source of leaks and related problems.

Waterproof membranes

Waterproof membranes shouldn't be confused with the irrigation system. They are typical of flat roofs, and include synthetic rubber roofing compounds and other synthetic materials. They are essential to keep water out of homes. Liquid applied asphalt is a common option.

When selecting a membrane pay attention to its lifetime and other warranties. A 20-year lifetime is a common warranty.

Insulation layer

Some green roofs do not use a specific insulation layer. They are by themselves a piece – and an extremely power one – of that insulation. But in some cases, to get an even higher insulation power, green roofs also include a specific insulation layer, usually based on a rigid synthetic board foam.