Green rooftops are the creative soul’s dream.   The possibilities are never ending with what you can do to make a rooftop green.   Aesthetically, you have curb appeal.   Environmentally, you put more oxygen into the air.  Economically you have energy savings, not to mention a very unique building.   Garden rooftops are still relatively uncommon in the United States (which is also why there is a dearth of green rooftop builders here), whereas in Europe, the beauty and utility of garden rooftops have long been a tradition.   You need not visit Germany to view some gorgeous rooftop gardens in Chicago.   In fact, you need not go further than the green-roofed City Hall Building Downtown.     With all of the advantages for the practical mind and the beauty of the idealistic mind, a green rooftop satisfies all.

Remember that being green structurally can take many forms and is inclusive.     You can be green by placing planters on a patio if that’s the best options in your dwelling.     Should you have a flat rooftop, an intensive garden would be perfect.   Remember, the intensive garden is significantly heavier and requires more maintenance because of the delicate varieties of plants they tend to have.   Also note that your intensive garden will mean your roof must be able to withstand the weight of your garden.     Your situation might be condo living, and there will be rules that you’ll need to follow in your garden.   The extensive garden, the lower maintenance option, also works well on a flat rooftop or one that is gently sloped.   It’s less expensive to install and maintain and much lighter.   Whatever you decide, some basic principles will apply to the process.

The ideal is to build a house with a green roof from scratch.   That way, you can do it right, with features such as a waterproof membrane and root-resistant layer.   You can work with your existing roof, but consider that it might not be perfect.   Your roof might have hidden leaks or some other hidden damage.   Your roof may lack the structural integrity to withstand the weight of an intensive garden.   That is where a structural engineer or architect comes in.   Have a structural analysis performed to answer these areas in question, and you’ll move forward with the knowledge that, for instance, your roof can’t withstand an intensive garden but can support an extensive one just fine.

You might also learn through the analysis that you can modify your home structurally to support your dream of an intensive garden.   Keep in mind that more costs will be involved with a project such as a reinforcement.     Once you have everything in writing with the help of a professional engineer/architect, you can confidently move forward to meeting builders, horticulturists, designers, and other experts along the way.

Imagine the privacy of rooftop gardening.   You won’t miss the vermin when your gardening expands from the ground to the rooftop.   Just how will you access your rooftop Eden?   Accessibility is a key consideration.   From the construction process of hauling materials to the top of the roof to the touring when you take a group of your friends (or maybe just one or two depending on the weight capacity of your roof) on a tour of your green roof, you’ll need to have two separate exit paths, according to Chicago’s Building Code.

Just how many people can you take on you rooftop tour at one time?     You’ll need to consider the weight of the type garden you want.   An intensive garden weighs significantly more than an extensive one (extensive roofs weigh about 20-34 pounds per square foot; intensive roofs weigh about 80-150 pounds per square foot).   You will surely have this information after your structural analysis is made by that engineer or architect we met earlier.   In determining weight, your engineer will evaluate what systems you plan to use for water storage (water stored in a tank weighs about 8 pounds per gallon); what types of plants you will be using (hopefully they will be indigenous to Illinois); heating, cooling and ventilation systems; and snow weight (Chicago Municipal Code requires at least 30 pounds per square foot for design snow load).     Once you make these determinations, you’ll have a better idea of how many friends you can take onto that roof at one time.

Unless you’re lucky enough to be building a house green from the beginning, depending on your structural analysis, you will want to budget for modifications.   You can be as creative as you wish to fit your budget.   However, you want this done right from the beginning or it will really be costly.   You want safety.   You want proper irrigation.   You want the right materials.   Most importantly, you want the right people to be advising you.   Note that a green roof on average costs about 50% more than a traditional roof.   As you might expect, the extensive roof, the lower-maintenance featherweight, is less expensive than the higher-maintenance intensive heavyweight.     Don’t let that scare you.   Compared to a traditional rooftop, extensive and intensive green rooftops can increase the life of your roof by about 50%.   Why?   Your garden is an excellent natural protector against the elements that could pummel the life out of a bare conventional roof.

So, how much rainwater will those thirsty rooftop plants drink up?   They drink up the rainwater very well, and you’ll have much less runoff with a garden rooftop.   The water that the plants or growing media don’t drink up-or that exceeds the levels of your water storage device-will need to be drained off your rooftop properly.   Think of the heavy burden you would be putting on your roof with all of this extra water.   The solutions?   Nothing fancy.   Downspouts, gutters, drains, and screens, to name a few.     You will have information from your structural analysis as far as drainage systems and what you’ll need to handle heavy rain and snowfall and maintain the best conditions for growing your plants.

Now that you have some basic elements of planning, another “P” word is “permit.”   Before your construction begins, you’ll need to have the Chicago Department of Buildings review your plans and then obtain a permit.   For a standalone house, you can draw the plans yourself if you like, or your architect can do this for you.   For a building with more than one unit and for commercial structures, an architect licensed in Illinois must draw the plans.   Also note semantics.     A “rooftop garden” is interpreted as a garden that will be accessible to people (remember the two mandatory exits?) versus the “green roof,” where access will be limited to maintenance, but no garden parties will be held.

Remember, your means are far less relevant than creativity in making your home green.   Beautiful containers artfully housing beautiful plants on a patio may be just green enough for you.

Images courtesy of American Hydrotech, Inc.

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