Why does Greenroofs.com call them greenroofs
and not green roofs?
For a variety of reasons: a
term is more descriptive and exact in its meaning, like dishwasher or
are household words included in the dictionary, meaning the combination of
their parts. A dish washer, for example, is something or more commonly,
someone, who washes dishes but a dishwasher is obviously a machine
that washes the dishes. A green roof could refer to the fact that any of
the roofing material is ecologically sound, or green in nature, such as a
recycled or naturally harvested product, or uses sustainable design elements
in some way. "Green" can be applied to energy-efficient components,
such as highly reflective roofing membranes (e.g., white single plies or
modified bituminous roof systems topped with reflective coatings), or roofs
of sprayed polyurethane foam.
A green roof could also refer to the color of the roofing
material, be it green ceramic tiles, metal, or asphalt shingles.
We did so much original information searching in
German, that it was just natural that we should call them greenroofs, as
they are referred to as Dachbegrünungen
roof greenings or greened roofs. Of course, the German language always
joins nouns for descriptive purposes, but it really does convey the meaning
of a particular word. I dont think anyone could confuse the meaning of
greenroof a vegetated roof cover, be it extensive or intensive.
OK, so what is a greenroof?
Basically, greenroofs are vegetated roof covers, with
growing media and plants taking the place of bare membrane, gravel ballast,
shingles or tiles. The number of layers and the layer placement vary from
system to system and greenroof type, but at the very least all greenroofs
include a single to multi-ply waterproofing layer, drainage, growing media
and the plants, covering the entire roof deck surface. There are two main
types of greenroofs extensive or
intensive - although a greenroof is often
designed with features of both and then are referred to as either
semi-extensive or semi-intensive.
I see you call yourselves "The Greenroof
Industry Resource Portal." What do you consider to be the "Greenroof
We consider the green roof
industry to be those who contribute in any capacity at large - including
those who choose to not be associated with any particular group or regional,
non-profit, professional, etc., organization. The
"greenroof industry" is not self-describing
other than that these individuals are active in the study, promotion,
construction, design or implementation of ideas and ideals within the
growing community of people interested in furthering the wide spread
implementation of this form of living architecture. "Industry" is meant to
describe the burgeoning commercial and professional arena, and is certainly
not limited to one particular "professional" organization's definition or
membership's restriction of what "the industry" should construe.
Industry can also mean "Community" or free and unencumbered "MarketPlace,"
for that matter.
Whats the difference between an extensive and
Commonly, the roof function or objective of the roof
space determines the design is it just an ecological cover or is it
intended for human recreation, vegetable gardening, etc.? The limiting
factors for greenroofs include: the roof loading capacity or maximum dead
and live weight loads, determined by a structural engineer; the slope of the
roof and perhaps the clients budget.
Also referred to as eco-roofs, and low-profile They have thinner and less
numbers of layers, so therefore they are lighter, less expensive and very
low maintenance. Extensive greenroofs are built when the primary desire is
for an ecological roof cover with limited human access. The minimum growing
media or soil substrate starts at about 2 1/2 to 6 at most (although
vegetative mats can actually have even less than 1" of growth media); the engineered
soil media contains 70 80% inorganic or mineral material (or higher) to 20
30% organic (or less). Low growing, horizontally spreading root ground
covers with general maximum plant heights of 16 24 are ideal.
Alpine-type plants are successful because they are high drought, wind,
frost, and heat tolerant, all necessary attributes for greenroofs. Plants
include sedums and other succulents, flowering herbs, and certain grasses
and mosses. Fully saturated weights range from a low of about 10 50
lbs/sq. ft. Compare that to common river rock ballast which weighs about 12
lbs/sq. ft. Extensive greenroofs can be constructed on slopes up to 30°,
and steeper ones can be installed with raised grids or laths to hold
plants and soil media in place.
Also referred to as high-profile They look like traditional roof gardens
because a much wider variety of plant material can be included since growing
media depths are increased. The growing media starts from about 8 - 12 and
can range up to 15 feet or more, depending on the loading capacity of the
roof and the architectural and plant features that the building owner
desires. The engineered soil media usually contains about 45 - 50% organic
material to 50 - 55% mineral, and fully saturated weights range from about
80 -120 lbs/sq. ft. and up. Architectural accents such as waterfalls,
ponds, gazebos, etc. are possible and these greenroofs provide recreation
spaces and encourage interaction between people and nature. Maintenance
requirements are also more intensive, and of course, these roofs are
Whats the difference between an intensive
greenroof and a roof garden?
A roof garden usually consists of containerized
plantings of various sizes placed on top of a roof. In an intensive
greenroof system, all the various layers are applied on top of the entire
roof deck surface, allowing unimpeded drainage and a more even weight
distribution over the whole roof. The vegetation is planted directly into
the soil, not in planters or containers.
Explain inorganic and organic growth media.
material refers to a high porosity natural mineral element such as expanded
slate, shale, extruded clay, rock wool, lava or pumice, etc., which provides
aeration (and could also provide water retention capabilities), and prevents
total compaction of organic matter through settling over time, and acts as a
good drainage medium. The inorganic medium maintains void or air space
necessary for the plant roots to breathe and for the excess water to drain
means well-rotted humus material (hen manure, guano, mushroom
compost, etc.) augmented with organic fibrous material and a small amount of
clay particles. This mixture holds and slowly releases essential trace
elements necessary for the health of the soil community.
Is an extensive greenroof really
No! Every roof needs to be checked periodically, and
extensive greenroofs are no different. It is recommended to do a
semi-annual maintenance review, at which time you can look for invasive
weeds, disease, stray tree seedlings, etc. Plants, no matter how low
growing and drought tolerant, are still living, breathing beings and should
Do I have to water my greenroof?
occasionally during the first year of establishment just like any
landscape. Drip irrigation is ideal for large projects plus it is
inexpensive and delivers the right amount of water to the best area the
base of the plants. But then the answer should be no, if you have chosen
the correct drought tolerant plants wisely for your area, except in extreme
periods of drought. Then the plants would certainly benefit from occasional
watering during extreme periods of duress thats one reason a water source
should be close by.
Intensive Yes, since
an intensive greenroof can accommodate a large variety of plants, shrubs and
trees, their watering requirements are higher than succulents and herbs.
Treat an intensive greenroof like any garden or landscape at ground level,
but take into account that high winds can be very drying. Usually large
intensive greenroofs have an irrigation system installed.
So what about irrigation or supplemental water
can it still be environmentally friendly?
Yes. You can install a traditional active irrigation
system or a solar powered system. Pair this with a recycled rainwater
collection system, harvested in cisterns at roof deck or at ground level,
and youve got the ideal self-sustainable answer to supplemental water and
how to power it.
Should I fertilize my extensive greenroof?
There is some dissention about whether it is
recommended or not to fertilize an extensive greenroof I believe the
answer is yes, as most German roof greening professionals recommend. Use
encapsulated slow release fertilizer twice during the first year of
establishment in the early spring and fall, and then yearly thereafter for
the next 4 years or so. At that point, the natural cycle should take over
and enough organic material should have composted itself back into the soil
substrate to provide sufficient nutrients to the plants. Dont use soluble
N fertilizer as it can get into the runoff.
Do I have to worry about a root-resistant
protective layer if I only have an extensive greenroof with nothing but
Yes! Just because you design a greenroof with tiny
horizontal roots, it doesnt mean you cant get a surprise plant with a huge
taproot looking for water however they can get it. Seeds come in from many
sources the wind, and from those beautiful birds that you love seeing on
your greenroof so much. I have seen oak and maple seedlings growing in ½
of rotted compost on a pitched roof, for example. And, believe me, those
roots will seek water wherever possible in times of drought way into the
asphalt membrane! If your roofing membrane is organic in nature asphalt,
asphaltic bitumen, etc., you need a root barrier, it doesn't matter how low
growing your extensive greenroof plants are. It needs to be a dense
inorganic material that inhibits root penetration, like polyethylene. This
protective layer can be a heavy duty pond liner (EPDM, etc.) or other
non-organic element that contains an injected root repellent, such as a
copper element. Also, many North American drainage products bypass a
separate root barrier layer and now incorporate a root-repellent ingredient
in their synthetic filter fabric, placed atop the drainage layer.
Does the soil really have to be engineered?
Why cant I just put top soil on my greenroof?
Yes! Regular garden soil is heavy, can contain
pathogens, undesirable insects, and WEEDS! Basically, you dont know whats
in it. Think potting soils in that really they are engineered soiless
media. Greenroof soils need to be lightweight to conform to roof loading
weight restrictions, drain properly and yet retain a certain amount of rain
water. Some designers will approve a certain amount of topsoil to reduce
costs, but great care needs to be taken with this option. In this case, a
typical mix is to use 1/3 clean topsoil, 1/3 compost, 1/3 perlite or other
Should I worry about flammability issues?
Yes! Always have access to an adequate water supply
just in case of fire, which can occur to any type of building. First of
all, choose plants that are inherently non-flammable succulents or others
that store water in their stems, and stay away from ornamental grasses and
certain mosses that could become kindling material in an extremely dry
situation. For example, Miscanthus can be very flammable. Succulent
plants and a high inorganic soil media can actually act as a fire barrier.
But make sure that your roof has a 12-24 perimeter of vegetation free zone
around the edges of the roof both for a fire break and for sure-footed
access of firefighters to the roof. This can be crushed gravel, pebbles or
Who should maintain my roof?
It depends on the type and size of the greenroof. Most
homeowners could check a flat or low pitch greenroof. A roofing
professional should if it is too large or intensive you can include a
maintenance agreement of at least twice per year with the greenroof
contractor/greenroof company. Or you can work out an arrangement with the
roof maintenance staff of your building. And if you are referring to an
elaborate hotel roof garden, for example, there will be a garden staff for
maintenance needs already.
What about costs?
Extensive Ive seen
them listed as low as about $9/sq .ft. for 3 of growing media and sedums.
More commonly the range is between $14 - $25/sq. ft., (including roofing
$25 - $40
But every project is unique, and certainly there are
ways to lower the costs. Economy of scale is also very relevant. The Ford
Motor Company River Rouge Plant greenroof in Dearborn, MI, for example, came
in around $4/sq. ft., but were also talking about an extensive greenroof
thats almost 500,000 sq. ft in size.
Which is the most expensive component of a
Just like any roof, the waterproofing membrane (or
membranes) is the single highest cost item of a new roof.
Why shouldnt you plant just sod or grass on a
roof? They did it that way in Scandinavia and northern North America for
hundreds of years.
Sod roofs resulted from a lack of natural resources, so
people had to use the only materials they had at hand. But a monoculture of
plant species is never considered healthy nor is desired in a land or
roofscape for a variety of reasons: It would be open to plant disease, or
an insect infestation could wipe it out. A monoculture is simply not
ecological in nature a plant community should be ecologically diverse
with many types of vegetation to be vibrant (just like the human world
think The Boys from Brazil). Grass or sod needs to be watered,
fertilized, and cut regularly, so they would incur greater costs be
considered high maintenance.
Are greenroofs necessarily green in color?
No! Many greenroofs appear red, orange, yellow and all
colors in between at different times of the year because the fleshy leaves
of various succulents change colors throughout the year. Also, greenroof
plants are not all evergreen, nor should they be. The beauty and
anticipation of the change of seasons add to the color palette. And of
course, flowers vary, too, in colors from whites to yellow, pinks, deep reds
and purples and blues. A virtual living carpet or tapestry varies from
season to season as plant communities naturally migrate in their random
Where can I find info
about different greenroof projects?
Greenroof Projects Database, which is international in scope,
growing daily, and a free community resource. Submit your projects for
free by using the easy
online form and send us your logo for placement at the top of the Project
Profile as the "Information Partner." You can refine your search using
over 15 fields.
So if I do a
particular defined search in a variety of fields, does that mean that all
the greenroof projects in the world are truly listed here?
continues to gather profiles from various sources across the globe, and many
are in the works from various organizations, manufacturers, designers,
owners, etc. It will probably take several years to catalogue all
these projects properly, but that is one of our missions!
Can you recommend a greenroof designer or
specific company? Where can I find this information?
No, Greenroofs.com does not recommend specific people
or companies, but you will find manufacturers, suppliers & designers listed
in The Greenroof Directory and related products and accessories in
How many LEEDpoints
can a greenroof qualify for?
Greenroofs can contribute
to at least 6 LEED points (more are possible) up to a possible 15 or 16.
New info shows that greenroofs can contribute up to 14 credits with
LEED-NC, Version 2.2. See more info
here, and consult a LEED
Accredited Professional for specifics.
for more general information.
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