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Installing a Green Roof (Roof
Top Garden)
Green roofs are alternatives to traditional
roofing. Basically they are a rooftop garden, mainly conceived
to cool buildings and to reduce air conditioning costs.
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 confirm the capacity of the
roof to support the weight of the green roof. There are indeed
several questions you should pay attention, connected to the
several layers involved in the green roof.
Pay attention to the types of plants, or
to issues as the soil, the
irrigation and drainage layer, the
root barrier or the
waterproof membrane layer.
Types of Roof Top Gardens
The characteristics of a green roof may vary. 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 more regular maintenance is usually
limited to the first months.
There are, anyway, larger and more ambitious
types of green roofs, involving larger amounts of soil depth
(one foot minimum), large shrubs and trees, and very regular
maintenance requirements and complex drainage and irrigation
systems. This type of green roof is characteristic of large
buildings, and is commonly called intensive green roofs.
Layers of a green roof
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
adapted to your local climate conditions. 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 in a top roof garden
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. Waterproof membranes 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
level, green roofs also include a specific insulation layer,
usually based on a rigid synthetic board foam.
See also:
Green roofs costs, pros and cons
Roof basics
Roof membranes and coatings
Metal and ceramic roof
materials
Roofing and environment
Roofs and climates
Attic insulation
Roof and ceiling
insulation
Reflective
insulation
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